U.S. patent application number 15/174923 was filed with the patent office on 2016-09-29 for methods and compositions for targeted nucleic acid sequencing.
The applicant listed for this patent is 10X Genomics, Inc.. Invention is credited to Benjamin Hindson, Mirna Jarosz, Serge Saxonov, Michael Schnall-Levin, Xinying Zheng.
Application Number | 20160281137 15/174923 |
Document ID | / |
Family ID | 54540216 |
Filed Date | 2016-09-29 |
United States Patent
Application |
20160281137 |
Kind Code |
A1 |
Jarosz; Mirna ; et
al. |
September 29, 2016 |
METHODS AND COMPOSITIONS FOR TARGETED NUCLEIC ACID SEQUENCING
Abstract
The present invention is directed to methods, compositions and
systems for capturing and analyzing sequence information contained
in targeted regions of a genome. Such targeted regions may include
exomes, partial exomes, introns, combinations of exonic and
intronic regions, genes, panels of genes, and any other subsets of
a whole genome that may be of interest.
Inventors: |
Jarosz; Mirna; (Mountain
View, CA) ; Schnall-Levin; Michael; (Palo Alto,
CA) ; Saxonov; Serge; (Oakland, CA) ; Hindson;
Benjamin; (Pleasanton, CA) ; Zheng; Xinying;
(Mountain View, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
10X Genomics, Inc. |
Pleasanton |
CA |
US |
|
|
Family ID: |
54540216 |
Appl. No.: |
15/174923 |
Filed: |
June 6, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14927297 |
Oct 29, 2015 |
|
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15174923 |
|
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62072164 |
Oct 29, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C12Q 1/6806 20130101;
C12Q 1/6806 20130101; C12Q 1/6837 20130101; C12Q 2535/122 20130101;
C12Q 2565/514 20130101; C12Q 2535/122 20130101; C12Q 2537/159
20130101; C12Q 2563/179 20130101; C12Q 2565/514 20130101; C12Q
2537/159 20130101; C12Q 1/6874 20130101; C12Q 1/6874 20130101 |
International
Class: |
C12Q 1/68 20060101
C12Q001/68 |
Claims
1. A method of obtaining sequence information from one or more
targeted portions of a genomic sample, the method comprising: (a)
generating a plurality of barcoded fragments from a plurality of
individual nucleic acid molecules from the genomic sample, wherein
the individual nucleic acid molecules have lengths greater than 1
kilobase (kb), and wherein fragments from the same individual
nucleic molecule comprise a common barcode; (b) enriching the
plurality of barcoded fragments with fragments comprising sequences
associated with a disease or disorder, thereby producing an
enriched plurality of fragments; and (c) conducting a sequencing
reaction to identify sequences of the enriched plurality of
fragments, thereby obtaining sequence information from the one or
more targeted portions of the genomic sample.
2. The method of claim 1, wherein the disease or disorder is
cancer.
3. The method of claim 1, wherein the genomic sample is from a
tumor.
4. The method of claim 1, wherein the genomic sample is from a
pregnant woman who is at risk of carrying a baby with a birth
defect.
5. The method of claim 1, wherein the enriching step (b) comprises:
(i) hybridizing probes complementary to regions in or near the one
or more targeted portions of the genomic samples to the barcoded
fragments to form probe-fragment complexes; (ii) capturing the
probe-fragment complexes to a surface of a solid support; thereby
enriching the plurality of barcoded fragments with fragments
comprising sequences associated with a disease or disorder.
6. The method of claim 5, wherein the probes comprise binding
moieties and the surface comprises capture moieties, and wherein
the probe-fragment complexes are captured on the surface through a
reaction between the binding moieties and the capture moieties.
7. The method of claim 6, wherein the capture moieties are directed
to a member selected from the group consisting of: whole or partial
exome capture, panel capture, targeted exon capture, anchored exome
capture, and tiled genomic region capture.
8. The method of claim 6, wherein the binding moieties comprise
biotin and the capture moieties comprise streptavidin.
9. The method of claim 1, wherein the sequencing reaction is a
short read, high accuracy sequencing reaction.
10. The method of claim 1, wherein prior to the enriching step (b),
the barcoded fragments are amplified such that the resultant
amplification products are capable of forming partial or complete
hairpin structures.
11. The method of claim 1, wherein the individual nucleic acid
molecules have lengths greater than 10 kb.
12. The method of claim 1, wherein the individual nucleic acid
molecules have lengths greater than 20 kb.
13. The method of claim 1, wherein the sequencing reaction is a
short read, high accuracy sequencing reaction.
14. The method of claim 1, wherein the method further comprises
step (d) determining linkage of two or more targeted portions of
the genomic sample based upon common barcode sequences.
15. The method of claim 1, wherein the two or more targeted
portions of the genomic sample comprise about 45-95% of the genomic
sample.
16. The method of claim 1, wherein the two or more targeted
portions of the genomic sample comprise about 35-80% of the genomic
sample.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/927,297, filed Oct. 29, 2015, which claims the benefit of
U.S. Provisional Application No. 62/072,164, filed Oct. 29, 2014,
each of which is expressly incorporated herein by reference in
their entirety for all purposes.
BACKGROUND OF THE INVENTION
[0002] The ability to sequence genomes accurately and rapidly is
revolutionizing biology and medicine. The study of complex genomes,
and in particular, the search for the genetic basis of disease in
humans, involves genetic analysis on a massive scale. Such genetic
analysis on a whole genome level is costly not only monetarily but
also in time and labor. These costs increase with protocols
involving analyses of separate individual DNA samples. Sequencing
(and re-sequencing) of polymorphic areas in the genome that are
linked to disease development will contribute greatly to the
understanding of diseases, such as cancer, and therapeutic
development and will help meet the pharmacogenomics challenge to
identify the genes and functional polymorphisms associated with the
variability in drug response. Screens for numerous genetic markers
performed for populations large enough to yield statistically
significant data are needed before associations can be made between
a given genotype and a particular disease.
[0003] One way to reduce the costs associated with genome
sequencing while retaining the benefits of genomic analysis on a
large scale is to perform high throughput, high accuracy sequencing
on targeted regions of the genome. A widely used approach captures
much of the entire protein coding region of a genome (the exome),
which makes up about 1% of the human genome, and has become a
routine technique in clinical and basic research. Exome sequencing
offers advantages over whole genome sequencing: it is significantly
less expensive, is more easily understood for functional
interpretation, is significantly faster to analyze, makes very deep
sequencing affordable, and results in a dataset that is easier to
manage. A need exists for methods, systems and compositions for the
enrichment of target regions of interest for high accuracy and high
throughput sequencing and genetic analysis.
SUMMARY OF THE INVENTION
[0004] Accordingly, the present invention provides methods, systems
and compositions for obtaining sequence information for targeted
regions of the genome.
[0005] In some aspects, the present disclosure provides a method
for sequencing one or more selected portions of a genome, the
method generally including the steps of: (a) providing starting
genomic material, (b) distributing individual nucleic acid
molecules from the starting genomic material into discrete
partitions such that each discrete partition contains a first
individual nucleic acid molecule; (c) fragmenting the individual
nucleic acid molecules in the discrete partitions to form a
plurality of fragments, where each of the fragments further
includes a barcode, and where fragments within a given discrete
partition each include a common barcode, thereby associating each
fragment with the individual nucleic acid molecule from which it is
derived; (d) providing a population enriched for fragments
including at least a portion of the one or more selected portions
of the genome; (e) obtaining sequence information from the
population, thereby sequencing one or more selected portions of a
genome.
[0006] In further embodiments and in accordance with the above,
providing the population enriched for fragments including at least
a portion of the one or more selected portions of the genome
includes the steps of (i) hybridizing probes complementary to
regions in or near the one or more selected portions of the genome
to the fragments to form probe-fragment complexes; and (ii)
capturing probe-fragment complexes to a surface of a solid support;
thereby enriching the population with fragments including at least
a portion of the one or more selected portions of the genome. In
yet further embodiments, the solid support includes a bead. In
still further embodiments, the probes include binding moieties and
the surface include capture moieties, and the probe-fragment
complexes are captured on the surface through a reaction between
the binding moieties and the capture moieties. In further examples,
the capture moieties include streptavidin and the binding moieties
include biotin. In still further examples, the capture moieties
comprise streptavidin magnetic beads and the binding moieties
comprise biotinylated RNA library baits.
[0007] In some embodiments and in accordance with any of the above,
the methods of the invention include the use of capture moieties
that are directed to whole or partial exome capture, panel capture,
targeted exon capture, anchored exome capture, or tiled genomic
region capture.
[0008] In yet further embodiments and in accordance with any of the
above, the methods disclosed herein include an obtaining step that
includes a sequencing reaction. In further embodiments, the
sequencing reaction is a short read-length sequencing reaction or a
long read-length sequencing reaction. In still further examples,
the sequencing reaction provides sequence information on less than
90%, less than 75%, or less than 50% of the starting genomic
material.
[0009] In still further embodiments, the methods described herein
further include linking two or more of the individual nucleic acid
molecules in an inferred contig based upon overlapping sequences of
the isolated fragments, wherein the inferred contig comprises a
length N50 of at least 10 kb, 20 kb, 40 kb, 50 kb, 100 kb, or 200
kb.
[0010] In yet further examples and in accordance with any of the
above, the methods disclosed herein further include linking two or
more of the individual nucleic acid molecules in a phase block
based upon overlapping phased variants within the sequences of the
isolated fragments, where the phase block comprises a length N50 of
at least 10 kb, of at least 20 kb, of at least 40 kb, of at least
50 kb, of at least 100 kb or of at least 200 kb.
[0011] In still further embodiments and in accordance with any of
the above, the methods disclosed herein provide sequence
information from selected portions of the genome that together
cover an exome. In yet further embodiments, the individual nucleic
acid molecules in the discrete partitions include genomic DNA from
a single cell. In still further embodiments, the discrete
partitions each include genomic DNA from a different
chromosome.
[0012] In further aspects, the present disclosure provides a method
of obtaining sequence information from one or more targeted
portions of a genomic sample. Such a method includes without
limitation the steps of: (a) providing individual first nucleic
acid fragment molecules of the genomic sample in discrete
partitions; (b) fragmenting the individual first nucleic acid
fragment molecules within the discrete partitions to create a
plurality of second fragments from each of the individual first
nucleic acid fragment molecules; (c) attaching a common barcode
sequence to the plurality of the second fragments within a discrete
partition, such that each of the plurality of second fragments are
attributable to the discrete partition in which they are contained;
(d) applying a library of probes directed to the one or more
targeted portions of the genomic sample to the second fragments;
(e) conducting a sequencing reaction to identify sequences of the
plurality of second fragments that hybridized to the library of
probes, thereby obtaining sequence information from the one or more
targeted portions of the genomic sample. In further embodiments,
the library of probes are attached to binding moieties, and before
the conducting step (e), the second fragments are captured on a
surface comprising capture moieties through a reaction between the
binding moieties and the capture moieties. In still further
embodiments and prior to the conducting step (e), the second
fragments are amplified before or after the second fragments are
captured on the surface. In yet further embodiments, the binding
moieties comprise biotin and the capture moieties comprise
streptavidin. In still further embodiments, the sequencing reaction
is a short read, high accuracy sequencing reaction. In still
further embodiments, the second fragments are amplified such that
the resultant amplification products are capable of forming partial
or complete hairpin structures.
[0013] In further aspects and in accordance with any of the above,
the present disclosure provides methods for obtaining sequence
information from one or more targeted portions of a genomic sample
while retaining molecular context. Such methods include the steps
of: (a) providing starting genomic material; (b) distributing
individual nucleic acid molecules from the starting genomic
material into discrete partitions such that each discrete partition
contains a first individual nucleic acid molecule; (c) fragmenting
the first individual nucleic acid molecules in the discrete
partitions to form a plurality of fragments; (d) providing a
population enriched for fragments that include at least a portion
of the one or more selected portions of the genome; (e) obtaining
sequence information from the population, thereby sequencing one or
more targeted portions of the genomic sample while retaining
molecular context. In further embodiments, prior to the obtaining
step (e), the plurality of fragments are tagged with a barcode to
associate each fragment with the discrete partition in which it was
formed. In still further embodiments, the individual nucleic acid
molecules in step (b) are distributed such that molecular context
of each first individual nucleic acid molecule is maintained.
[0014] In some aspects, the present disclosure provides methods of
obtaining sequence information from one or more targeted portions
of a genomic sample. Such methods include without limitation steps
of (a) providing individual nucleic acid molecules of the genomic
sample; (b) fragmenting the individual nucleic acid molecules to
form a plurality of fragments, where each of the fragments further
includes a barcode, and where fragments from the same individual
nucleic molecule have a common barcode, thereby associating each
fragment with the individual nucleic acid molecule from which it is
derived; (c) enriching the plurality of fragments for fragments
containing the one or more targeted portions of the genomic sample;
and (d) conducting a sequencing reaction to identify sequences of
the enriched plurality of fragments, thereby obtaining sequence
information from the one or more targeted portions of the genomic
sample. In further embodiments, the enriching step including
applying a library of probes directed to the one or more targeted
portions of the genomic sample. In yet further embodiments, the
library of probes are attached to binding moieties, and prior to
the conducting step, the fragments are captured through a reaction
between the binding moieties and the capture moieties. In exemplary
embodiments, the reaction between the binding moieties and the
capture moieties immobilizes the fragments on a surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 provides a schematic illustration of identification
and analysis of targeted genomic regions using conventional
processes versus the processes and systems described herein.
[0016] FIG. 2A and FIG. 2B provide schematic illustrations of
identification and analysis of targeted genomic regions using
processes and systems described herein.
[0017] FIG. 3 illustrates a typical workflow for performing an
assay to detect sequence information, using the methods and
compositions disclosed herein.
[0018] FIG. 4 provides a schematic illustration of a process for
combining a nucleic acid sample with beads and partitioning the
nucleic acids and beads into discrete droplets.
[0019] FIG. 5 provides a schematic illustration of a process for
barcoding and amplification of chromosomal nucleic acid
fragments.
[0020] FIG. 6 provides a schematic illustration of the use of
barcoding of chromosomal nucleic acid fragments in attributing
sequence data to individual chromosomes.
[0021] FIG. 7 illustrates a general embodiment of a method of the
invention.
[0022] FIG. 8 illustrates a general embodiment of a method of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The practice of the present invention may employ, unless
otherwise indicated, conventional techniques and descriptions of
organic chemistry, polymer technology, molecular biology (including
recombinant techniques), cell biology, biochemistry, and
immunology, which are within the skill of the art. Such
conventional techniques include polymer array synthesis,
hybridization, ligation, phage display, and detection of
hybridization using a label. Specific illustrations of suitable
techniques can be had by reference to the example herein below.
However, other equivalent conventional procedures can, of course,
also be used. Such conventional techniques and descriptions can be
found in standard laboratory manuals such as Genome Analysis: A
Laboratory Manual Series (Vols. I-IV), Using Antibodies: A
Laboratory Manual, Cells: A Laboratory Manual, PCR Primer: A
Laboratory Manual, and Molecular Cloning: A Laboratory Manual (all
from Cold Spring Harbor Laboratory Press), Stryer, L. (1995)
Biochemistry (4th Ed.) Freeman, New York, Gait, "Oligonucleotide
Synthesis: A Practical Approach" 1984, IRL Press, London, Nelson
and Cox (2000), Lehninger, Principles of Biochemistry 3.sup.rd Ed.,
W. H. Freeman Pub., New York, N.Y. and Berg et al. (2002)
Biochemistry 5.sup.th Ed., W. H. Freeman Pub., New York, N.Y., all
of which are herein incorporated in their entirety by reference for
all purposes.
[0024] Note that as used herein and in the appended claims, the
singular forms "a," "an," and "the" include plural referents unless
the context clearly dictates otherwise. Thus, for example,
reference to "a polymerase" refers to one agent or mixtures of such
agents, and reference to "the method" includes reference to
equivalent steps and methods known to those skilled in the art, and
so forth.
[0025] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. All
publications mentioned herein are incorporated herein by reference
for the purpose of describing and disclosing devices, compositions,
formulations and methodologies which are described in the
publication and which might be used in connection with the
presently described invention.
[0026] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limit of that range and any other stated or intervening
value in that stated range is encompassed within the invention. The
upper and lower limits of these smaller ranges may independently be
included in the smaller ranges is also encompassed within the
invention, subject to any specifically excluded limit in the stated
range. Where the stated range includes one or both of the limits,
ranges excluding either both of those included limits are also
included in the invention.
[0027] In the following description, numerous specific details are
set forth to provide a more thorough understanding of the present
invention. However, it will be apparent to one of skill in the art
that the present invention may be practiced without one or more of
these specific details. In other instances, well-known features and
procedures well known to those skilled in the art have not been
described in order to avoid obscuring the invention.
[0028] As used herein, the term "comprising" is intended to mean
that the compositions and methods include the recited elements, but
not excluding others. "Consisting essentially of" when used to
define compositions and methods, shall mean excluding other
elements of any essential significance to the composition or
method. "Consisting of" shall mean excluding more than trace
elements of other ingredients for claimed compositions and
substantial method steps. Embodiments defined by each of these
transition terms are within the scope of this invention.
Accordingly, it is intended that the methods and compositions can
include additional steps and components (comprising) or
alternatively including steps and compositions of no significance
(consisting essentially of) or alternatively, intending only the
stated method steps or compositions (consisting of).
[0029] All numerical designations, e.g., pH, temperature, time,
concentration, and molecular weight, including ranges, are
approximations which are varied (+) or (-) by increments of 0.1. It
is to be understood, although not always explicitly stated that all
numerical designations are preceded by the term "about". The term
"about" also includes the exact value "X" in addition to minor
increments of "X" such as "X+0.1" or "X-0.1." It also is to be
understood, although not always explicitly stated, that the
reagents described herein are merely exemplary and that equivalents
of such are known in the art.
I. Overview
[0030] This disclosure provides methods, compositions and systems
useful for characterization of genetic material. In particular, the
methods, compositions and systems described herein provide genetic
characterization of targeted regions of a genome, including without
limitation particular chromosomes, regions of chromosomes, all
exons (exomes), portions of exomes, specific genes, panels of genes
(e.g., kinomes or other targeted gene panels), intronic regions,
tiled portions of a genome, or any other chosen portion of a
genome.
[0031] In general, the methods and systems described herein
accomplish targeted genomic sequencing by providing for the
determination of the sequence of long individual nucleic acid
molecules and/or the identification of direct molecular linkage as
between two sequence segments separated by long stretches of
sequence, which permit the identification and use of long range
sequence information, but this sequencing information is obtained
using methods that have the advantages of the extremely low
sequencing error rates and high throughput of short read sequencing
technologies. The methods and systems described herein segment long
nucleic acid molecules into smaller fragments that can be sequenced
using high-throughput, higher accuracy short-read sequencing
technologies, and that segmentation is accomplished in a manner
that allows the sequence information derived from the smaller
fragments to retain the original long range molecular sequence
context, i.e., allowing the attribution of shorter sequence reads
to originating longer individual nucleic acid molecules. By
attributing sequence reads to an originating longer nucleic acid
molecule, one can gain significant characterization information for
that longer nucleic acid sequence that one cannot generally obtain
from short sequence reads alone. This long range molecular context
is not only preserved through a sequencing process, but is also
preserved through the targeted enrichment process used in targeted
sequencing approaches described herein, where no other sequencing
approach has shown this ability.
[0032] In general, sequence information from smaller fragments will
retain the original long range molecular sequence context through
the use of a tagging procedure, including the addition of barcodes
as described herein and known in the art. In specific examples,
fragments originating from the same original longer individual
nucleic acid molecule will be tagged with a common barcode, such
that any later sequence reads from those fragments can be
attributed to that originating longer individual nucleic acid
molecule. Such barcodes can be added using any method known in the
art, including addition of barcode sequences during amplification
methods that amplify segments of the individual nucleic acid
molecules as well as insertion of barcodes into the original
individual nucleic acid molecules using transposons, including
methods such as those described in Amini et al., Nature Genetics
46: 1343-1349 (2014) (advance online publication on Oct. 29, 2014),
which is hereby incorporated by reference in its entirety for all
purposes and in particular for all teachings related to adding
adaptor and other oligonucleotides using transposons. Once nucleic
acids have been tagged using such methods, the resultant tagged
fragments can be enriched using methods described herein such that
the population of fragments represents targeted regions of the
genome. As such, sequence reads from that population allows for
targeted sequencing of select regions of the genome, and those
sequence reads can also be attributed to the originating nucleic
acid molecules, thus preserving the original long range molecular
sequence context. The sequence reads can be obtained using any
sequencing methods and platforms known in the art and described
herein.
[0033] In addition to providing the ability to obtain sequence
information from targeted regions of the genome, the methods and
systems described herein can also provide other characterizations
of genomic material, including without limitation haplotype
phasing, identification of structural variations, and identifying
copy number variations, as described in co-pending applications
U.S. Ser. Nos. 14/752,589 and 14/752,602, both filed on Jun. 26,
2015), which are herein incorporated by reference in their entirety
for all purposes and in particular for all written description,
figures and working examples directed to characterization of
genomic material.
[0034] Methods of processing and sequencing nucleic acids in
accordance with the methods and systems described in the present
application are also described in further detail in U.S. Ser. Nos.
14/316,383; 14/316,398; 14/316,416; 14/316,431; 14/316,447; and
14/316,463 which are herein incorporated by reference in their
entirety for all purposes and in particular for all written
description, figures and working examples directed to processing
nucleic acids and sequencing and other characterizations of genomic
material.
[0035] In general, as shown in FIG. 1, the methods and systems
described herein may be used to characterize nucleic acids. In
particular, as shown, two discrete individual nucleic acids 102 and
104 are illustrated, each having a number of regions of interest,
e.g., region 106 and 108 in nucleic acid 102, and regions 110 and
112 in nucleic acid 104. The regions of interest in each nucleic
acid are linked within the same nucleic acid molecule, but may be
relatively separated from each other, e.g., more than 1 kb apart,
more than 5 kb apart, more than 10 kb apart, more than 20 kb apart,
more than 30 kb apart, more than 40 kb apart, more than 50 kb
apart, and in some cases, as much as 100 kb apart. The regions may
denote individual genes, gene groups, exons, or simply discrete and
separate parts of the genome. Solely for ease of discussion, the
regions shown in FIG. 1 will be referred to as exons 106, 108, 110
and 112. As shown, each nucleic acid 102 and 104 is separated into
its own partition 114 and 116, respectively. As noted elsewhere
herein, these partitions are, in many cases, aqueous droplets in a
water in oil emulsion. Within each droplet, portions of each
fragment are copied in a manner that preserves the original
molecular context of those fragments, e.g., as having originated
from the same molecule. As shown, this is achieved through the
inclusion in each copied fragment of a barcode sequence, e.g.,
barcode sequence "1" or "2" as illustrated, that is representative
of the droplet into which the originating fragment was partitioned.
For whole genome sequence analysis applications, one could simply
pool all of the copied fragments and their associated barcodes, in
order to sequence and reassemble the full range sequence
information from each of the originating nucleic acids 102 and 104.
However, in many cases, it is more desirable to only analyze
specific targeted portions of the overall genome, e.g., the exome,
specific genes, or the like, in order to provide greater focus on
scientifically relevant portions of the genome, and to minimize the
time and expense of performing sequencing on less relevant or
irrelevant portions of the genome.
[0036] In accordance with the methods described herein, target
enrichment steps may be applied to the libraries of barcoded
sequence fragments in order to "pull down" the sequences associated
with the desired targets. These may include exon targeted pull
downs, gene panel specific targeted pull downs, or the like. A
large number of targeted pull down kits that allow for the enriched
separation of specific targeted regions of the genome are
commercially available, such as the Agilent SureSelect exome pull
down kits, and the like. As shown in FIG. 1, application of a
targeted enrichment results in enriched, barcoded sequence library
118. Further, because the pulled down fragments within library 118
retain their original molecular context, e.g., through the
retention of the barcode information, they may be reassembled into
their original molecular contexts with embedded long range linkage
information, e.g., with inferred linkage as between each of the
assembled regions of interest 106:108 and 110:112. By way of
example, one may identify direct molecular linkage between two
disparate targeted portions of the genome, e.g., two or more exons,
and that direct molecular linkage may be used to identify
structural variations and other genomic characteristics, as well as
to identify the phase information as to the two or more exons, e.g.
providing phased exons, including potentially an entire phased
exome, or other phased targeted portions of a genome.
[0037] Generally, methods of the invention include steps as
illustrated in FIG. 7, which provides a schematic overview of
methods of the invention discussed in further detail herein. As
will be appreciated, the method outlined in FIG. 9 is an exemplary
embodiment that may be altered or modified as needed and as
described herein.
[0038] As shown in FIG. 7, the methods described herein will in
most examples include a step in which sample nucleic acids
containing the targeted regions of interest are partitioned (701).
Generally, each partition will include a single individual nucleic
acid molecule from a particular locus that is then fragmented or
copied in such a way as to preserve the original molecular context
of the fragments (702), usually by barcoding the fragments that are
specific to the partition in which they are contained. Each
partition may in some examples include more than one nucleic acid,
and will in some instances contain several hundred nucleic acid
molecules--in situations in which multiple nucleic acids are within
a partition, any particular locus of the genome will generally be
represented by a single individual nucleic acid prior to barcoding.
The barcoded fragments of step 702 can be generated using any
methods known in the art--in some examples, oligonucleotides are
the samples within the distinct partitions. Such oligonucleotides
may comprise random sequences intended to randomly prime numerous
different regions of the samples, or they may comprise a specific
primer sequence targeted to prime upstream of a targeted region of
the sample. In further examples, these oligonucleotides also
contain a barcode sequence, such that the replication process also
barcodes the resultant replicated fragment of the original sample
nucleic acid. A particularly elegant process for use of these
barcode oligonucleotides in amplifying and barcoding samples is
described in detail in U.S. patent application Ser. Nos.
14/316,383, 14/316,398, 14/316,416, 14/316,431, 14/316,447,
14/316,463, all filed Jun. 26, 2014, each of which is herein
incorporated by reference in its entirety for all purposes.
Extension reaction reagents, e.g., DNA polymerase, nucleoside
triphosphates, co-factors (e.g., Mg.sup.2+ or Mn.sup.2+ etc.), that
are also contained in the partitions, then extend the primer
sequence using the sample as a template, to produce a complementary
fragment to the strand of the template to which the primer
annealed, and the complementary fragment includes the
oligonucleotide and its associated barcode sequence. Annealing and
extension of multiple primers to different portions of the sample
can result in a large pool of overlapping complementary fragments
of the sample, each possessing its own barcode sequence indicative
of the partition in which it was created. In some cases, these
complementary fragments may themselves be used as a template primed
by the oligonucleotides present in the partition to produce a
complement of the complement that again, includes the barcode
sequence. In further examples, this replication process is
configured such that when the first complement is duplicated, it
produces two complementary sequences at or near its termini to
allow the formation of a hairpin structure or partial hairpin
structure, which reduces the ability of the molecule to be the
basis for producing further iterative copies.
[0039] Returning to the method exemplified in FIG. 7, once the
partition-specific barcodes are attached to the copied fragments,
the barcoded fragments are then pooled (703). Target enrichment
techniques can then be applied (704) to "pull down" the targeted
regions of interest. Those targeted regions of interest are then
sequenced (705) and the sequences of the fragments are attributed
to their originating molecular context (706), such that the
targeted regions of interest are both identified and also linked
with that originating molecular context. A unique feature of the
methods and systems described herein and illustrated in FIG. 7 is
that barcodes are attached to the fragments (702) prior to the
targeted enrichment step (704). An advantage of the methods and
systems described herein is that attaching a partition- or
sample-specific barcode to the copied fragments prior to enriching
the fragments for targeted genomic regions preserves the original
molecular context of those targeted regions, allowing them to be
attributed to their original partition and thus their originating
sample nucleic acid.
[0040] In general, targeted genomic regions are enriched, isolated
or separated, i.e., "pulled down," for further analysis,
particularly sequencing, using methods that include both chip-based
and solution-based capture methods. Such methods utilize probes
that are complementary to the genomic regions of interest or to
regions near or adjacent to the genomic regions of interest. For
example, in hybrid (or chip-based) capture, microarrays containing
capture probes (usually single-stranded oligonucleotides) with
sequences that taken together cover the region of interest are
fixed to a surface. Genomic DNA is fragmented and may further
undergo processing such as end-repair to produce blunt ends and/or
addition of additional features such as universal priming
sequences. These fragments are hybridized to the probes on the
microarray. Unhybridized fragments are washed away and the desired
fragments are eluted or otherwise processed on the surface for
sequencing or other analysis, and thus the population of fragments
remaining on the surface is enriched for fragments containing the
targeted regions of interest (e.g., the regions comprising the
sequences complementary to those contained in the capture probes).
The enriched population of fragments may further be amplified using
any amplification technologies known in the art.
[0041] Additional methods of targeted genomic region capture
include solution-based methods, in which genomic DNA fragments are
hybridized to oligonucleotide probes. The oligonucleotide probes
are often referred to as "baits". These baits are generally
attached to a capture molecule, including without limitation a
biotin molecule. The baits are complementary to targeted regions of
the genome (or to regions near or adjacent to the targeted regions
of interest), such that upon application to genomic DNA fragments,
the baits hybridize to the fragments, and the capture molecule
(e.g., biotin) is then used to selectively pull down the targeted
regions of interest (for example, with magnetic streptavidin beads)
to thereby enrich the resultant population of fragments with those
containing the targeted regions of interest.
[0042] In examples in which targeted regions covering the whole
exome are needed, a library of baits that together cover the whole
exome is used to capture those targeted sequences. In such
examples, capture protocols can include any of those known in the
art, including without limitation any of the exome capture
protocols and kits produced by Roche/NimbleGen, IIlumina, and
Agilent.
[0043] Capture of targeted genomic regions for use in the methods
and systems described herein are not limited to whole exomes, and
can include any one or combination of partial exomes, genes, panels
of genes, introns, and combinations of introns and exons. The
procedure for capture of these different types of targeted regions
follows the general method of using baits to pull down fragments
containing the targeted regions of interest. The design of the
baits, particularly the oligonucleotide probe portions of the baits
that hybridize to or near to the targeted regions of interest, will
in part depend on the type of targeted region to be captured.
[0044] In examples in which only a partial exome is needed for
further analysis, the baits can be designed to capture that part of
the exome. In certain examples, the specific identities of the
portions of the exome that are needed are known, and the library of
baits comprises oligonucleotides that are complementary to those
identified portions or to regions that are near or adjacent to
those portions. Such examples can further include without
limitation capture of specific genes and/or panels of genes, or
identified portions of the exome known to be associated with a
particular phenotype, such as a disorder or disease. In some
examples, it may be that a certain portion of the exome or the
whole genome (including both intronic and exonic regions) is needed
for further analysis, but the specific sequences for the portions
of the genome to be captured are not known. In such embodiments,
the baits used can be subsets of a library directed to a whole
genome, and that subset can be chosen randomly or through any kind
of intelligent design in which the library of baits is selected or
enriched for probes that are complementary to the targeted
subsections of the genome or exome.
[0045] For any of the methods described herein, the targeted
regions can be captured using baits that comprise oligonucleotide
probes that are complementary to the whole or part of a targeted
region, or the oligonucleotide probes may be complementary to
another region, e.g., an intronic region, that is near the targeted
region or adjacent to the targeted region. For example, as
schematically illustrated in FIG. 2A, a genomic sequence 201
comprises exonic regions 202 and 203. Those exonic regions can be
captured by directing the baits to one or more of the intronic
sequences nearby (for example intronic region 204 and/or 205 to
capture exonic region 202 and intronic region 206 for capture of
exonic region 203). In other words, a population of fragments
comprising exonic regions 202 or 203 can be captured through the
use of baits complementary to intronic regions 204 and/or 205 and
206. As shown in FIG. 2A, the intronic region used as an intronic
bait for the nearby exonic region can be adjacent to the exonic
region of interest--i.e., there is no gap between the intronic
region and the targeted exonic region. In other examples, the
intronic region used to capture the nearby exonic region may be
near enough so that both regions are likely to be in the same
fragment, but there is a gap of one or more nucleotides between the
exonic region and the intronic region (for example 202 and 205 in
FIG. 2A).
[0046] In some examples, rather than designing the baits to target
particular regions of the genome, a tiling approach is used. In
such an approach, rather than targeting specific exonic or intronic
regions, the baits are designed to be complementary to portions of
the genome at particular ranges or distances. For example, the
library of baits can be designed to cover sequences every 5
kilobases (kb) along the genome, such that applying this library of
baits to a fragmented genomic sample will capture only a certain
subset of the genome--i.e., those regions that are contained in
fragments containing complementary sequences to the baits. As will
be appreciated, the baits can be designed based on a reference
sequence, such as a human genome reference sequence. In further
examples, the tiled library of baits is designed to capture regions
every 1, 2, 5, 10, 15, 20, 25, 50, 100, 200, 250, 500, 750, 1000,
or 10000 kilobases of a genome. In still further examples, the
tiled library of baits is designed to capture a mixture of
distances--that mixture can be a random mixture of distances or
intelligently designed such that a specific portion or percentage
of the genome is captured. As will be appreciated, such tiling
methods of capture will capture both intronic and exonic regions of
the genome for further analysis such as sequencing. Any of the
tiling or other intronic baiting methods described herein provide a
way to link sequence information from exons widely separated by
long intervening intronic regions.
[0047] In further examples, the tiling or other capture methods
described herein will capture about 5%, 10%, 15%, 20%, 30%, 40%,
50%, 60%, 70%, 80%, 90%, 95% of the whole genome. In still further
examples, the capture methods described herein capture about 1-10%,
5-20%, 10-30%, 15-40%, 20-50%, 25-60%, 30-70%, 35-80%, 40-90%, or
45-95% of the whole genome.
[0048] In some examples, sample preparation methods, including
methods of fragmenting, amplifying, partitioning, and otherwise
processing genomic DNA, can lead to biases or lower coverage of
certain regions of a genome. Such biases or lowered coverage can be
compensated for in the methods and systems disclosed herein by
altering the concentration or genomic locations of baits used to
capture targeted regions of the genome. In some examples, it may be
known that certain regions of the genome containing high GC content
or other structural variations will lead to low coverage--in such
situations, the library of baits can be altered to increase the
concentration of baits directed to those regions of low
coverage--in other words, the population of baits used may be
"spiked" to ensure that a sufficient number of fragments containing
targeted regions of the genome in those low coverage areas are
obtained in the final population of fragments to be sequenced. Such
spiking of baits may be conducted in commercially available whole
exome kits, such that a custom library of baits directed toward the
lower coverage regions are added to off-the-shelf exome capture
kits. Additionally, baits can be design to target a region of the
genome that is very close to the region of interest, but has more
favorable coverage, as is also discussed in further detail herein
and embodiments of which are schematically illustrated in FIG.
2.
[0049] In further examples, the library of baits used in methods of
the present invention is a product of informed design that fulfills
one or more characteristics as further described herein. This
informed design includes instances in which the library of baits is
directed to informative single nucleotide polymorphisms (SNPs). The
term "informative SNPs" as used herein refers to SNPs that are
heterozygous. The library of baits in some examples is designed to
contain a plurality of probes that are directed to regions of the
genomic sample that contain informative SNPs. By "directed to" as
used herein is meant that the probes contain sequences that are
complementary to sequences that encompass the SNPs. In further
examples, the library of baits is designed to contain probes
directed to SNPs that are at predetermined distances from the
boundary of an exon and an intron. In situations in which the
targeted regions of the genome include regions that are devoid of
or contain very few SNPs, the library of baits includes probes that
tile across such regions at a predetermined distance and/or that
hybridize to the first informative SNP within the next nearest
intron or exon.
[0050] An advantage of the methods and systems described herein is
that the targeted regions that are captured are processed prior to
capture in such a way that even after the steps of capturing the
targeted regions and conducting sequencing analyses, the original
molecular context of those targeted regions is retained. As is
discussed in further detail herein, the ability to attribute
specific targeted regions to their original molecular context
(which can include the original chromosome or chromosomal region
from which they are derived and/or the location of particular
targeted regions in relation to each other within the full genome)
provides a way to obtain sequence information from regions of the
genome that are otherwise poorly mapped or have poor coverage using
traditional sequencing techniques.
[0051] For example, some genes possess long introns that are too
long to span using generally available sequencing techniques,
particularly using short-read technologies that possess superior
accuracy as compared to long-read technologies. In the methods and
systems described herein, however, the molecular context of
targeted regions is retained, generally through the tagging
procedure illustrated in FIG. 1 and described in further detail
herein. As such, links can be made across extended regions of the
genome. For example, as schematically illustrated in FIG. 2B,
nucleic acid molecule 207 contains two exons (shaded bars)
interrupted by a long intronic region (208). Generally used
sequencing technologies would be unable to span the distance across
the intron to provide information on the relationship of the two
exons. In the methods described herein, the individual nucleic acid
molecule 207 is distributed into its own discrete partition 209 and
then fragmented such that different fragments contain different
portions of the exons and the intron. Because each of those
fragments is tagged such that any sequence information obtained
from the fragments is then attributable to the discrete partition
in which it was generated, each fragment is thus also attributable
to the individual nucleic acid molecule 207 from which it was
derived. In general, and as is described in further detail herein,
after fragmentation and tagging, fragments from different
partitions are combined together. Targeted capture methods can then
be used to enrich the population of fragments that undergoes
further analysis, such as sequencing, with fragments containing the
targeted region of interest. In the example illustrated in FIG. 2B,
the baits used will enrich the population of fragments to capture
only those containing a portion of one of the two exons and/or part
of the intervening intron, but regions outside of the exons and
intron (such as 209 and 210) would not be captured. Thus, the final
population of fragments that undergoes sequencing will be enriched
for the fragments containing portions of the two exons of interest.
Short read, high accuracy sequencing technologies can then be used
to identify the sequences of this enriched population of fragments,
and because each of the fragments is tagged and thus attributable
to its original molecular context, i.e., its original individual
nucleic acid molecule, the short read sequences can provide
information that spans over the long length of the intervening
intron to provide information on the relationship between the two
exons.
[0052] As noted above, the methods and systems described herein
provide individual molecular context for short sequence reads of
longer nucleic acids. As used herein, individual molecular context
refers to sequence context beyond the specific sequence read, e.g.,
relation to adjacent or proximal sequences, that are not included
within the sequence read itself, and as such, will typically be
such that they would not be included in whole or in part in a short
sequence read, e.g., a read of about 150 bases, or about 300 bases
for paired reads. In particularly preferred aspects, the methods
and systems provide long range sequence context for short sequence
reads. Such long range context includes relationship or linkage of
a given sequence read to sequence reads that are within a distance
of each other of longer than 1 kb, longer than 5 kb, longer than 10
kb, longer than 15 kb, longer than 20 kb, longer than 30 kb, longer
than 40 kb, longer than 50 kb, longer than 60 kb, longer than 70
kb, longer than 80 kb, longer than 90 kb or even longer than 100
kb, or longer. As will be appreciated, by providing long range
individual molecular context, one can also derive the phasing
information of variants within that individual molecular context,
e.g., variants on a particular long molecule will be, by definition
commonly phased.
[0053] By providing longer range individual molecular context, the
methods and systems of the invention also provide much longer
inferred molecular context (also referred to herein as a "long
virtual single molecule read"). Sequence context, as described
herein can include mapping or providing linkage of fragments across
different (generally on the kilobase scale) ranges of full genomic
sequence. These methods include mapping the short sequence reads to
the individual longer molecules or contigs of linked molecules, as
well as long range sequencing of large portions of the longer
individual molecules, e.g., having contiguous determined sequences
of individual molecules where such determined sequences are longer
than 1 kb, longer than 5 kb, longer than 10 kb, longer than 15 kb,
longer than 20 kb, longer than 30 kb, longer than 40 kb, longer
than 50 kb, longer than 60 kb, longer than 70 kb, longer than 80
kb, longer than 90 kb or even longer than 100 kb. As with sequence
context, the attribution of short sequences to longer nucleic
acids, e.g., both individual long nucleic acid molecules or
collections of linked nucleic acid molecules or contigs, may
include both mapping of short sequences against longer nucleic acid
stretches to provide high level sequence context, as well as
providing assembled sequences from the short sequences through
these longer nucleic acids.
[0054] Furthermore, while one may utilize the long range sequence
context associated with long individual molecules, having such long
range sequence context also allows one to infer even longer range
sequence context. By way of one example, by providing the long
range molecular context described above, one can identify
overlapping variant portions, e.g., phased variants, translocated
sequences, etc., among long sequences from different originating
molecules, allowing the inferred linkage between those molecules.
Such inferred linkages or molecular contexts are referred to herein
as "inferred contigs". In some cases when discussed in the context
of phased sequences, the inferred contigs may represent commonly
phased sequences, e.g., where by virtue of overlapping phased
variants, one can infer a phased contig of substantially greater
length than the individual originating molecules. These phased
contigs are referred to herein as "phase blocks".
[0055] By starting with longer single molecule reads (e.g., the
"long virtual single molecule reads" discussed above), one can
derive longer inferred contigs or phase blocks than would otherwise
be attainable using short read sequencing technologies or other
approaches to phased sequencing. See, e.g., published U.S. Patent
Application No. 2013-0157870. In particular, using the methods and
systems described herein, one can obtain inferred contig or phase
block lengths having an N50 (where the sum of the block lengths
that are greater than the stated N50 number is 50% of the sum of
all block lengths) of at least about 10 kb, at least about 20 kb,
at least about 50 kb. In more preferred aspects, inferred contig or
phase block lengths having an N50 of at least about 100 kb, at
least about 150 kb, at least about 200 kb, and in many cases, at
least about 250 kb, at least about 300 kb, at least about 350 kb,
at least about 400 kb, and in some cases, at least about 500 kb or
more, are attained. In still other cases, maximum phase block
lengths in excess of 200 kb, in excess of 300 kb, in excess of 400
kb, in excess of 500 kb, in excess of 1 Mb, or even in excess of 2
Mb may be obtained.
[0056] In one aspect, and in conjunction with any of the capture
methods described above and later herein, the methods and systems
described herein provide for the compartmentalization, depositing
or partitioning of sample nucleic acids, or fragments thereof, into
discrete compartments or partitions (referred to interchangeably
herein as partitions), where each partition maintains separation of
its own contents from the contents of other partitions. Unique
identifiers, e.g., barcodes, may be previously, subsequently or
concurrently delivered to the partitions that hold the
compartmentalized or partitioned sample nucleic acids, in order to
allow for the later attribution of the characteristics, e.g.,
nucleic acid sequence information, to the sample nucleic acids
included within a particular compartment, and particularly to
relatively long stretches of contiguous sample nucleic acids that
may be originally deposited into the partitions.
[0057] The sample nucleic acids utilized in the methods described
herein typically represent a number of overlapping portions of the
overall sample to be analyzed, e.g., an entire chromosome, exome,
or other large genomic portion. These sample nucleic acids may
include whole genomes, individual chromosomes, exomes, amplicons,
or any of a variety of different nucleic acids of interest. The
sample nucleic acids are typically partitioned such that the
nucleic acids are present in the partitions in relatively long
fragments or stretches of contiguous nucleic acid molecules.
Typically, these fragments of the sample nucleic acids may be
longer than 1 kb, longer than 5 kb, longer than 10 kb, longer than
15 kb, longer than 20 kb, longer than 30 kb, longer than 40 kb,
longer than 50 kb, longer than 60 kb, longer than 70 kb, longer
than 80 kb, longer than 90 kb or even longer than 100 kb, which
permits the longer range molecular context described above.
[0058] The sample nucleic acids are also typically partitioned at a
level whereby a given partition has a very low probability of
including two overlapping fragments of the starting sample nucleic
acid. This is typically accomplished by providing the sample
nucleic acid at a low input amount and/or concentration during the
partitioning process. As a result, in preferred cases, a given
partition may include a number of long, but non-overlapping
fragments of the starting sample nucleic acids. The sample nucleic
acids in the different partitions are then associated with unique
identifiers, where for any given partition, nucleic acids contained
therein possess the same unique identifier, but where different
partitions may include different unique identifiers. Moreover,
because the partitioning step allocates the sample components into
very small volume partitions or droplets, it will be appreciated
that in order to achieve the desired allocation as set forth above,
one need not conduct substantial dilution of the sample, as would
be required in higher volume processes, e.g., in tubes, or wells of
a multiwell plate. Further, because the systems described herein
employ such high levels of barcode diversity, one can allocate
diverse barcodes among higher numbers of genomic equivalents, as
provided above. In particular, previously described, multiwell
plate approaches (see, e.g., U.S. Published Application No.
2013-0079231 and 2013-0157870) typically only operate with a
hundred to a few hundred different barcode sequences, and employ a
limiting dilution process of their sample in order to be able to
attribute barcodes to different cells/nucleic acids. As such, they
will generally operate with far fewer than 100 cells, which would
typically provide a ratio of genomes:(barcode type) on the order of
1:10, and certainly well above 1:100. The systems described herein,
on the other hand, because of the high level of barcode diversity,
e.g., in excess of 10,000, 100,000, 500,000, etc. diverse barcode
types, can operate at genome:(barcode type) ratios that are on the
order of 1:50 or less, 1:100 or less, 1:1000 or less, or even
smaller ratios, while also allowing for loading higher numbers of
genomes (e.g., on the order of greater than 100 genomes per assay,
greater than 500 genomes per assay, 1000 genomes per assay, or even
more) while still providing for far improved barcode diversity per
genome.
[0059] Often, the sample is combined with a set of oligonucleotide
tags that are releasably-attached to beads prior to the
partitioning step. That combination can then lead to barcoding of
nucleic acids in the samples using methods known in the art and
described herein. In some examples, amplification methods are used
to add barcodes to the resultant amplification products, which in
some examples contain smaller segments (fragments) of the full
originating nucleic acid molecule from which they are derived. In
some examples, methods using transposons are utilized as described
in Amini et al, Nature Genetics 46: 1343-1349 (2014) (advance
online publication on Oct. 29, 2014), which is herein incorporated
by reference in its entirety for all purposes and in particular for
all teachings related to attaching barcodes or other
oligonucleotide tags to nucleic acids. In further examples, methods
of attaching barcodes can include the use of nicking enzymes or
polymerases and/or invasive probes such as recA to produce gaps
along double stranded sample nucleic acids--barcodes can then be
inserted into those gaps.
[0060] In examples in which amplification is used to tag nucleic
acid fragments, the oligonucleotide tags may comprise at least a
first and second region. The first region may be a barcode region
that, as between oligonucleotides within a given partition, may be
substantially the same barcode sequence, but as between different
partitions, may and, in most cases is a different barcode sequence.
The second region may be an N-mer (either a random N-mer or an
N-mer designed to target a particular sequence) that can be used to
prime the nucleic acids within the sample within the partitions. In
some cases, where the N-mer is designed to target a particular
sequence, it may be designed to target a particular chromosome
(e.g., chromosome 1, 13, 18, or 21), or region of a chromosome,
e.g., an exome or other targeted region. In some cases, the N-mer
may be designed to target a particular gene or genetic region, such
as a gene or region associated with a disease or disorder (e.g.,
cancer). Within the partitions, an amplification reaction may be
conducted using the second N-mer to prime the nucleic acid sample
at different places along the length of the nucleic acid. As a
result of the amplification, each partition may contain amplified
products of the nucleic acid that are attached to an identical or
near-identical barcode, and that may represent overlapping, smaller
fragments of the nucleic acids in each partition. The bar-code can
serve as a marker that signifies that a set of nucleic acids
originated from the same partition, and thus potentially also
originated from the same strand of nucleic acid. Following
amplification, the nucleic acids may be pooled, sequenced, and
aligned using a sequencing algorithm. Because shorter sequence
reads may, by virtue of their associated barcode sequences, be
aligned and attributed to a single, long fragment of the sample
nucleic acid, all of the identified variants on that sequence can
be attributed to a single originating fragment and single
originating chromosome. Further, by aligning multiple co-located
variants across multiple long fragments, one can further
characterize that chromosomal contribution. Accordingly,
conclusions regarding the phasing of particular genetic variants
may then be drawn, as can analyses across long ranges of genomic
sequence--for example, identification of sequence information
across stretches of poorly characterized regions of the genome.
Such information may also be useful for identifying haplotypes,
which are generally a specified set of genetic variants that reside
on the same nucleic acid strand or on different nucleic acid
strands. Copy number variations may also be identified in this
manner.
[0061] The described methods and systems provide significant
advantages over current nucleic acid sequencing technologies and
their associated sample preparation methods. Ensemble sample
preparation and sequencing methods are predisposed towards
primarily identifying and characterizing the majority constituents
in the sample, and are not designed to identify and characterize
minority constituents, e.g., genetic material contributed by one
chromosome, or by one or a few cells, or fragmented tumor cell DNA
molecule circulating in the bloodstream, that constitute a small
percentage of the total DNA in the extracted sample. The described
methods and systems also provide a significant advantage for
detecting populations that are present within a larger sample. As
such, they are particularly useful for assessing haplotype and copy
number variations--the methods disclosed herein are also useful for
providing sequence information over regions of the genome that are
poorly characterized or are poorly represented in a population of
nucleic acid targets due to biases introduced during sample
preparation.
[0062] The use of the barcoding technique disclosed herein confers
the unique capability of providing individual molecular context for
a given set of genetic markers, i.e., attributing a given set of
genetic markers (as opposed to a single marker) to individual
sample nucleic acid molecules, and through variant coordinated
assembly, to provide a broader or even longer range inferred
individual molecular context, among multiple sample nucleic acid
molecules, and/or to a specific chromosome. These genetic markers
may include specific genetic loci, e.g., variants, such as SNPs, or
they may include short sequences. Furthermore, the use of barcoding
confers the additional advantages of facilitating the ability to
discriminate between minority constituents and majority
constituents of the total nucleic acid population extracted from
the sample, e.g. for detection and characterization of circulating
tumor DNA in the bloodstream, and also reduces or eliminates
amplification bias during optional amplification steps. In
addition, implementation in a microfluidics format confers the
ability to work with extremely small sample volumes and low input
quantities of DNA, as well as the ability to rapidly process large
numbers of sample partitions (droplets) to facilitate genome-wide
tagging.
[0063] As described previously, an advantage of the methods and
systems described herein is that they can achieve the desired
results through the use of ubiquitously available, short read
sequencing technologies. Such technologies have the advantages of
being readily available and widely dispersed within the research
community, with protocols and reagent systems that are well
characterized and highly effective. These short read sequencing
technologies include those available from, e.g., IIlumina, inc.
(GXII, NextSeq, MiSeq, HiSeq, X10), Ion Torrent division of
Thermo-Fisher (Ion Proton and Ion PGM), pyrosequencing methods, as
well as others.
[0064] Of particular advantage is that the methods and systems
described herein utilize these short read sequencing technologies
and do so with their associated low error rates. In particular, the
methods and systems described herein achieve the desired individual
molecular readlengths or context, as described above, but with
individual sequencing reads, excluding mate pair extensions, that
are shorter than 1000 bp, shorter than 500 bp, shorter than 300 bp,
shorter than 200 bp, shorter than 150 bp or even shorter; and with
sequencing error rates for such individual molecular readlengths
that are less than 5%, less than 1%, less than 0.5%, less than
0.1%, less than 0.05%, less than 0.01%, less than 0.005%, or even
less than 0.001%.
II. Work Flow Overview
[0065] In one exemplary aspect, the methods and systems described
in the disclosure provide for depositing or partitioning individual
samples (e.g., nucleic acids) into discrete partitions, where each
partition maintains separation of its own contents from the
contents in other partitions. As used herein, the partitions refer
to containers or vessels that may include a variety of different
forms, e.g., wells, tubes, micro or nanowells, through holes, or
the like. In preferred aspects, however, the partitions are
flowable within fluid streams. These vessels may be comprised of,
e.g., microcapsules or micro-vesicles that have an outer barrier
surrounding an inner fluid center or core, or they may be a porous
matrix that is capable of entraining and/or retaining materials
within its matrix. In preferred aspect, however, these partitions
may comprise droplets of aqueous fluid within a non-aqueous
continuous phase, e.g., an oil phase. A variety of different
vessels are described in, for example, U.S. patent application Ser.
No. 13/966,150, filed Aug. 13, 2013. Likewise, emulsion systems for
creating stable droplets in non-aqueous or oil continuous phases
are described in detail in, e.g., Published U.S. Patent Application
No. 2010-0105112. In certain cases, microfluidic channel networks
are particularly suited for generating partitions as described
herein. Examples of such microfluidic devices include those
described in detail in U.S. patent application Ser. No. 14/682,952,
filed Apr. 9, 2015, the full disclosure of which is incorporated
herein by reference in its entirety for all purposes. Alternative
mechanisms may also be employed in the partitioning of individual
cells, including porous membranes through which aqueous mixtures of
cells are extruded into non-aqueous fluids. Such systems are
generally available from, e.g., Nanomi, Inc.
[0066] In the case of droplets in an emulsion, partitioning of
sample materials, e.g., nucleic acids, into discrete partitions may
generally be accomplished by flowing an aqueous, sample containing
stream, into a junction into which is also flowing a non-aqueous
stream of partitioning fluid, e.g., a fluorinated oil, such that
aqueous droplets are created within the flowing stream partitioning
fluid, where such droplets include the sample materials. As
described below, the partitions, e.g., droplets, also typically
include co-partitioned barcode oligonucleotides. The relative
amount of sample materials within any particular partition may be
adjusted by controlling a variety of different parameters of the
system, including, for example, the concentration of sample in the
aqueous stream, the flow rate of the aqueous stream and/or the
non-aqueous stream, and the like. The partitions described herein
are often characterized by having extremely small volumes. For
example, in the case of droplet based partitions, the droplets may
have overall volumes that are less than 1000 pL, less than 900 pL,
less than 800 pL, less than 700 pL, less than 600 pL, less than 500
pL, less than 400 pL, less than 300 pL, less than 200 pL, less than
100 pL, less than 50 pL, less than 20 pL, less than 10 pL, or even
less than 1 pL. Where co-partitioned with beads, it will be
appreciated that the sample fluid volume within the partitions may
be less than 90% of the above described volumes, less than 80%,
less than 70%, less than 60%, less than 50%, less than 40%, less
than 30%, less than 20%, or even less than 10% the above described
volumes. In some cases, the use of low reaction volume partitions
is particularly advantageous in performing reactions with very
small amounts of starting reagents, e.g., input nucleic acids.
Methods and systems for analyzing samples with low input nucleic
acids are presented in U.S. patent application Ser. No. 14/752,602,
filed Jun. 26, 2015, the full disclosure of which is hereby
incorporated by reference in its entirety.
[0067] Once the samples are introduced into their respective
partitions, in accordance with the methods and systems described
herein, the sample nucleic acids within partitions are generally
provided with unique identifiers such that, upon characterization
of those nucleic acids they may be attributed as having been
derived from their respective origins. Accordingly, the sample
nucleic acids are typically co-partitioned with the unique
identifiers (e.g., barcode sequences). In particularly preferred
aspects, the unique identifiers are provided in the form of
oligonucleotides that comprise nucleic acid barcode sequences that
may be attached to those samples. The oligonucleotides are
partitioned such that as between oligonucleotides in a given
partition, the nucleic acid barcode sequences contained therein are
the same, but as between different partitions, the oligonucleotides
can, and preferably have differing barcode sequences. In preferred
aspects, only one nucleic acid barcode sequence will be associated
with a given partition, although in some cases, two or more
different barcode sequences may be present.
[0068] The nucleic acid barcode sequences will typically include
from 6 to about 20 or more nucleotides within the sequence of the
oligonucleotides. These nucleotides may be completely contiguous,
i.e., in a single stretch of adjacent nucleotides, or they may be
separated into two or more separate subsequences that are separated
by one or more nucleotides. Typically, separated subsequences may
typically be from about 4 to about 16 nucleotides in length.
[0069] The co-partitioned oligonucleotides also typically comprise
other functional sequences useful in the processing of the
partitioned nucleic acids. These sequences include, e.g., targeted
or random/universal amplification primer sequences for amplifying
the genomic DNA from the individual nucleic acids within the
partitions while attaching the associated barcode sequences,
sequencing primers, hybridization or probing sequences, e.g., for
identification of presence of the sequences, or for pulling down
barcoded nucleic acids, or any of a number of other potential
functional sequences. Again, co-partitioning of oligonucleotides
and associated barcodes and other functional sequences, along with
sample materials is described in, for example, U.S. Patent
Application Nos. U.S. patent application Ser. Nos. 14/316,383,
14/316,398, 14/316,416, 14/316,431, 14/316,447, 14/316,463, all
filed Jun. 26, 2014, as well as U.S. patent application Ser. No.
14/175,935, filed Feb. 7, 2014, the full disclosures of which is
hereby incorporated by reference in their entireties.
[0070] Briefly, in one exemplary process, beads are provided that
each may include large numbers of the above described
oligonucleotides releasably attached to the beads, where all of the
oligonucleotides attached to a particular bead may include the same
nucleic acid barcode sequence, but where a large number of diverse
barcode sequences may be represented across the population of beads
used. Typically, the population of beads may provide a diverse
barcode sequence library that may include at least 1000 different
barcode sequences, at least 10,000 different barcode sequences, at
least 100,000 different barcode sequences, or in some cases, at
least 1,000,000 different barcode sequences. Additionally, each
bead may typically be provided with large numbers of
oligonucleotide molecules attached. In particular, the number of
molecules of oligonucleotides including the barcode sequence on an
individual bead may be at least bout 10,000 oligonucleotides, at
least 100,000 oligonucleotide molecules, at least 1,000,000
oligonucleotide molecules, at least 100,000,000 oligonucleotide
molecules, and in some cases at least 1 billion oligonucleotide
molecules.
[0071] The oligonucleotides may be releasable from the beads upon
the application of a particular stimulus to the beads. In some
cases, the stimulus may be a photo-stimulus, e.g., through cleavage
of a photo-labile linkage that may release the oligonucleotides. In
some cases, a thermal stimulus may be used, where elevation of the
temperature of the beads environment may result in cleavage of a
linkage or other release of the oligonucleotides form the beads. In
some cases, a chemical stimulus may be used that cleaves a linkage
of the oligonucleotides to the beads, or otherwise may result in
release of the oligonucleotides from the beads.
[0072] In accordance with the methods and systems described herein,
the beads including the attached oligonucleotides may be
co-partitioned with the individual samples, such that a single bead
and a single sample are contained within an individual partition.
In some cases, where single bead partitions are desired, it may be
desirable to control the relative flow rates of the fluids such
that, on average, the partitions contain less than one bead per
partition, in order to ensure that those partitions that are
occupied, are primarily singly occupied. Likewise, one may wish to
control the flow rate to provide that a higher percentage of
partitions are occupied, e.g., allowing for only a small percentage
of unoccupied partitions. In preferred aspects, the flows and
channel architectures are controlled as to ensure a desired number
of singly occupied partitions, less than a certain level of
unoccupied partitions and less than a certain level of multiply
occupied partitions.
[0073] FIG. 3 illustrates one particular example method for
barcoding and subsequently sequencing a sample nucleic acid,
particularly for use for a copy number variation or haplotype
assay. First, a sample comprising nucleic acid may be obtained from
a source, 300, and a set of barcoded beads may also be obtained,
310. The beads are preferably linked to oligonucleotides containing
one or more barcode sequences, as well as a primer, such as a
random N-mer or other primer. Preferably, the barcode sequences are
releasable from the barcoded beads, e.g., through cleavage of a
linkage between the barcode and the bead or through degradation of
the underlying bead to release the barcode, or a combination of the
two. For example, in certain preferred aspects, the barcoded beads
can be degraded or dissolved by an agent, such as a reducing agent
to release the barcode sequences. In this example, a low quantity
of the sample comprising nucleic acid, 305, barcoded beads, 315,
and optionally other reagents, e.g., a reducing agent, 320, are
combined and subject to partitioning. By way of example, such
partitioning may involve introducing the components to a droplet
generation system, such as a microfluidic device, 325. With the aid
of the microfluidic device 325, a water-in-oil emulsion 330 may be
formed, wherein the emulsion contains aqueous droplets that contain
sample nucleic acid, 305, reducing agent, 320, and barcoded beads,
315. The reducing agent may dissolve or degrade the barcoded beads,
thereby releasing the oligonucleotides with the barcodes and random
N-mers from the beads within the droplets, 335. The random N-mers
may then prime different regions of the sample nucleic acid,
resulting in amplified copies of the sample after amplification,
wherein each copy is tagged with a barcode sequence, 340.
Preferably, each droplet contains a set of oligonucleotides that
contain identical barcode sequences and different random N-mer
sequences. Subsequently, the emulsion is broken, 345 and additional
sequences (e.g., sequences that aid in particular sequencing
methods, additional barcodes, etc.) may be added, via, for example,
amplification methods, 350 (e.g., PCR). Sequencing may then be
performed, 355, and an algorithm applied to interpret the
sequencing data, 360. Sequencing algorithms are generally capable,
for example, of performing analysis of barcodes to align sequencing
reads and/or identify the sample from which a particular sequence
read belongs. In addition, and as is described herein, these
algorithms may also further be used to attribute the sequences of
the copies to their originating molecular context.
[0074] As noted above, while single bead occupancy may be the most
desired state, it will be appreciated that multiply occupied
partitions or unoccupied partitions may often be present. An
example of a microfluidic channel structure for co-partitioning
samples and beads comprising barcode oligonucleotides is
schematically illustrated in FIG. 4. As shown, channel segments
402, 404, 406, 408 and 410 are provided in fluid communication at
channel junction 412. An aqueous stream comprising the individual
samples 414 is flowed through channel segment 402 toward channel
junction 412. As described elsewhere herein, these samples may be
suspended within an aqueous fluid prior to the partitioning
process.
[0075] Concurrently, an aqueous stream comprising the barcode
carrying beads 416 is flowed through channel segment 404 toward
channel junction 412. A non-aqueous partitioning fluid is
introduced into channel junction 412 from each of side channels 406
and 408, and the combined streams are flowed into outlet channel
410. Within channel junction 412, the two combined aqueous streams
from channel segments 402 and 404 are combined, and partitioned
into droplets 418, that include co-partitioned samples 414 and
beads 416. As noted previously, by controlling the flow
characteristics of each of the fluids combining at channel junction
412, as well as controlling the geometry of the channel junction,
one can optimize the combination and partitioning to achieve a
desired occupancy level of beads, samples or both, within the
partitions 418 that are generated.
[0076] As will be appreciated, a number of other reagents may be
co-partitioned along with the samples and beads, including, for
example, chemical stimuli, nucleic acid extension, transcription,
and/or amplification reagents such as polymerases, reverse
transcriptases, nucleoside triphosphates or NTP analogues, primer
sequences and additional cofactors such as divalent metal ions used
in such reactions, ligation reaction reagents, such as ligase
enzymes and ligation sequences, dyes, labels, or other tagging
reagents.
[0077] Once co-partitioned, the oligonucleotides disposed upon the
bead may be used to barcode and amplify the partitioned samples. A
particularly elegant process for use of these barcode
oligonucleotides in amplifying and barcoding samples is described
in detail in U.S. patent application Ser. Nos. 14/316,383,
14/316,398, 14/316,416, 14/316,431, 14/316,447, 14/316,463, all
filed Jun. 26, 2014, the full disclosures of which are hereby
incorporated by reference in their entireties. Briefly, in one
aspect, the oligonucleotides present on the beads that are
co-partitioned with the samples and released from their beads into
the partition with the samples. The oligonucleotides typically
include, along with the barcode sequence, a primer sequence at its
5' end. This primer sequence may be random or structured. Random
primer sequences are generally intended to randomly prime numerous
different regions of the samples. Structured primer sequences can
include a range of different structures including defined sequences
targeted to prime upstream of a specific targeted region of the
sample as well as primers that have some sort of partially defined
structure, including without limitation primers containing a
percentage of specific bases (such as a percentage of GC N-mers),
primers containing partially or wholly degenerate sequences, and/or
primers containing sequences that are partially random and
partially structured in accordance with any of the description
herein. As will be appreciated, any one or more of the above types
of random and structured primers may be included in
oligonucleotides in any combination.
[0078] Once released, the primer portion of the oligonucleotide can
anneal to a complementary region of the sample. Extension reaction
reagents, e.g., DNA polymerase, nucleoside triphosphates,
co-factors (e.g., Mg2+ or Mn2+ etc.), that are also co-partitioned
with the samples and beads, then extend the primer sequence using
the sample as a template, to produce a complementary fragment to
the strand of the template to which the primer annealed, with
complementary fragment includes the oligonucleotide and its
associated barcode sequence. Annealing and extension of multiple
primers to different portions of the sample may result in a large
pool of overlapping complementary fragments of the sample, each
possessing its own barcode sequence indicative of the partition in
which it was created. In some cases, these complementary fragments
may themselves be used as a template primed by the oligonucleotides
present in the partition to produce a complement of the complement
that again, includes the barcode sequence. In some cases, this
replication process is configured such that when the first
complement is duplicated, it produces two complementary sequences
at or near its termini, to allow the formation of a hairpin
structure or partial hairpin structure, which reduces the ability
of the molecule to be the basis for producing further iterative
copies. A schematic illustration of one example of this is shown in
FIG. 5.
[0079] As the figure shows, oligonucleotides that include a barcode
sequence are co-partitioned in, e.g., a droplet 502 in an emulsion,
along with a sample nucleic acid 504. As noted elsewhere herein,
the oligonucleotides 508 may be provided on a bead 506 that is
co-partitioned with the sample nucleic acid 504, which
oligonucleotides are preferably releasable from the bead 506, as
shown in panel A. The oligonucleotides 508 include a barcode
sequence 512, in addition to one or more functional sequences,
e.g., sequences 510, 514 and 516. For example, oligonucleotide 508
is shown as comprising barcode sequence 512, as well as sequence
510 that may function as an attachment or immobilization sequence
for a given sequencing system, e.g., a P5 sequence used for
attachment in flow cells of an Illumina Hiseq or Miseq system. As
shown, the oligonucleotides also include a primer sequence 516,
which may include a random or targeted N-mer for priming
replication of portions of the sample nucleic acid 504. Also
included within oligonucleotide 508 is a sequence 514 which may
provide a sequencing priming region, such as a "read1" or R1
priming region, that is used to prime polymerase mediated, template
directed sequencing by synthesis reactions in sequencing systems.
In many cases, the barcode sequence 512, immobilization sequence
510 and R1 sequence 514 may be common to all of the
oligonucleotides attached to a given bead. The primer sequence 516
may vary for random N-mer primers, or may be common to the
oligonucleotides on a given bead for certain targeted
applications.
[0080] Based upon the presence of primer sequence 516, the
oligonucleotides are able to prime the sample nucleic acid as shown
in panel B, which allows for extension of the oligonucleotides 508
and 508a using polymerase enzymes and other extension reagents also
co-portioned with the bead 506 and sample nucleic acid 504. As
shown in panel C, following extension of the oligonucleotides that,
for random N-mer primers, would anneal to multiple different
regions of the sample nucleic acid 504; multiple overlapping
complements or fragments of the nucleic acid are created, e.g.,
fragments 518 and 520. Although including sequence portions that
are complementary to portions of sample nucleic acid, e.g.,
sequences 522 and 524, these constructs are generally referred to
herein as comprising fragments of the sample nucleic acid 504,
having the attached barcode sequences. As will be appreciated, the
replicated portions of the template sequences as described above
are often referred to herein as "fragments" of that template
sequence. Notwithstanding the foregoing, however, the term
"fragment" encompasses any representation of a portion of the
originating nucleic acid sequence, e.g., a template or sample
nucleic acid, including those created by other mechanisms of
providing portions of the template sequence, such as actual
fragmentation of a given molecule of sequence, e.g., through
enzymatic, chemical or mechanical fragmentation. In preferred
aspects, however, fragments of a template or sample nucleic acid
sequence will denote replicated portions of the underlying sequence
or complements thereof.
[0081] The barcoded nucleic acid fragments may then be subjected to
characterization, e.g., through sequence analysis, or they may be
further amplified in the process, as shown in panel D. For example,
additional oligonucleotides, e.g., oligonucleotide 508b, also
released from bead 306, may prime the fragments 518 and 520. In
particular, again, based upon the presence of the random N-mer
primer 516b in oligonucleotide 508b (which in many cases will be
different from other random N-mers in a given partition, e.g.,
primer sequence 516), the oligonucleotide anneals with the fragment
518, and is extended to create a complement 526 to at least a
portion of fragment 518 which includes sequence 528, that comprises
a duplicate of a portion of the sample nucleic acid sequence.
Extension of the oligonucleotide 508b continues until it has
replicated through the oligonucleotide portion 508 of fragment 518.
As noted elsewhere herein, and as illustrated in panel D, the
oligonucleotides may be configured to prompt a stop in the
replication by the polymerase at a desired point, e.g., after
replicating through sequences 516 and 514 of oligonucleotide 508
that is included within fragment 518. As described herein, this may
be accomplished by different methods, including, for example, the
incorporation of different nucleotides and/or nucleotide analogues
that are not capable of being processed by the polymerase enzyme
used. For example, this may include the inclusion of uracil
containing nucleotides within the sequence region 512 to prevent a
non-uracil tolerant polymerase to cease replication of that region.
As a result a fragment 526 is created that includes the full-length
oligonucleotide 508b at one end, including the barcode sequence
512, the attachment sequence 510, the R1 primer region 514, and the
random N-mer sequence 516b. At the other end of the sequence will
be included the complement 516' to the random N-mer of the first
oligonucleotide 508, as well as a complement to all or a portion of
the R1 sequence, shown as sequence 514'. The R1 sequence 514 and
its complement 514' are then able to hybridize together to form a
partial hairpin structure 528. As will be appreciated because the
random N-mers differ among different oligonucleotides, these
sequences and their complements would not be expected to
participate in hairpin formation, e.g., sequence 516', which is the
complement to random N-mer 516, would not be expected to be
complementary to random N-mer sequence 516b. This would not be the
case for other applications, e.g., targeted primers, where the
N-mers would be common among oligonucleotides within a given
partition.
[0082] By forming these partial hairpin structures, it allows for
the removal of first level duplicates of the sample sequence from
further replication, e.g., preventing iterative copying of copies.
The partial hairpin structure also provides a useful structure for
subsequent processing of the created fragments, e.g., fragment
526.
[0083] All of the fragments from multiple different partitions may
then be pooled for sequencing on high throughput sequencers as
described herein. Because each fragment is coded as to its
partition of origin, the sequence of that fragment may be
attributed back to its origin based upon the presence of the
barcode. This is schematically illustrated in FIG. 6. As shown in
one example, a nucleic acid 604 originated from a first source 600
(e.g., individual chromosome, strand of nucleic acid, etc.) and a
nucleic acid 606 derived from a different chromosome 602 or strand
of nucleic acid are each partitioned along with their own sets of
barcode oligonucleotides as described above.
[0084] Within each partition, each nucleic acid 604 and 606 is then
processed to separately provide overlapping set of second fragments
of the first fragment(s), e.g., second fragment sets 608 and 610.
This processing also provides the second fragments with a barcode
sequence that is the same for each of the second fragments derived
from a particular first fragment. As shown, the barcode sequence
for second fragment set 608 is denoted by "1" while the barcode
sequence for fragment set 610 is denoted by "2". A diverse library
of barcodes may be used to differentially barcode large numbers of
different fragment sets. However, it is not necessary for every
second fragment set from a different first fragment to be barcoded
with different barcode sequences. In fact, in many cases, multiple
different first fragments may be processed concurrently to include
the same barcode sequence. Diverse barcode libraries are described
in detail elsewhere herein.
[0085] The barcoded fragments, e.g., from fragment sets 608 and
610, may then be pooled for sequencing using, for example, sequence
by synthesis technologies available from Illumina or Ion Torrent
division of Thermo Fisher, Inc. Once sequenced, the sequence reads
612 can be attributed to their respective fragment set, e.g., as
shown in aggregated reads 614 and 616, at least in part based upon
the included barcodes, and optionally, and preferably, in part
based upon the sequence of the fragment itself. The attributed
sequence reads for each fragment set are then assembled to provide
the assembled sequence for each sample fragment, e.g., sequences
618 and 620, which in turn, may be further attributed back to their
respective original chromosomes (600 and 602). Methods and systems
for assembling genomic sequences are described in, for example,
U.S. patent application Ser. No. 14/752,773, filed Jun. 26, 2015,
the full disclosure of which is hereby incorporated by reference in
its entirety.
III. Application of Methods and Systems to Targeted Sequencing
[0086] In one aspect of the systems and methods described herein
are used to obtain sequence information from targeted regions of a
genome.
[0087] By "targeted" regions of a genome (as well as any
grammatical equivalents thereof) is meant a whole genome or any one
or more regions of a genome identified as of interest and/or
selected through one or more methods described herein. The targeted
regions of the genome sequenced by methods and systems described
herein include without limitation introns, exons, intergenic
regions, or any combination thereof. In certain examples, the
methods and systems described herein provide sequence information
on whole exomes, portions of exomes, one or more selected genes
(including selected panels of genes), one or more introns, and
combinations of intronic and exonic sequences.
[0088] Targeted regions of the genome may also include certain
portions or percentages of the genome rather than regions
identified by sequence. In certain embodiments, targeted regions of
the genome captured and analyzed in accordance with the methods
described herein include portions of the genome located every 1, 2,
5, 10, 15, 20, 25, 50, 100, 200, 250, 500, 750, 1000, or 10000
kilobases of a genome. In further embodiments, targeted regions of
the genome comprise 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%,
80%, 90%, 95% of the whole genome. In still further embodiments,
the targeted regions comprise 1-10%, 5-20%, 10-30%, 15-40%, 20-50%,
25-60%, 30-70%, 35-80%, 40-90%, or 45-95% of the whole genome.
[0089] In general, targeted regions of a genome are captured for
use in any sequencing methods known in the art and described
herein. By "captured" as used herein is meant any method or system
for enriching a population of nucleic acid and/or nucleic acid
fragments such that the resultant population contains an increased
percentage of the targeted regions of interest as compared to the
genomic regions that are not of interest. In further embodiments,
the enriched population contains at least 50%, 55%, 60%, 70%, 75%,
80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100% nucleic acids/nucleic
acid fragments comprising the targeted regions.
[0090] Capture methods generally include chip-based methods, in
which targeted regions are captured through hybridization or other
association with capture molecules on a surface, and solution based
methods, in which oligonucleotide probes (baits), which are
complementary to the targeted regions (or to regions near the
targeted regions) are hybridized to genomic fragment libraries. The
probes used in the capture methods disclosed herein are generally
attached to capture molecules, such as biotin, which can be used to
"pull down" the probes and the fragments to which they are
hybridized--these pull down methods include any methods by which
the baits hybridized to nucleic acids or nucleic acid fragments
that contain the targeted regions of interest are separated from
fragments that do not contain the regions of interest. In
embodiments in which the probes are biotynilated, magnetic
streptavidin beads are used to selectively pull-down and enrich
baits with bound targeted regions.
[0091] In further aspects, a library of baits is used that covers
all the targeted regions desired for further study. In the case of
whole exome analysis, such a library of baits thus includes
oligonucleotide probes that together cover the full exome. In
certain embodiments, only portions of the exome are needed for
further analysis. In such embodiments, the baits are designed to
target that subset of the exome. This design can be accomplished
using methods and algorithms known in the art and in general is
based upon a reference sequence, such as the human genome.
[0092] In some examples, the targeted genomic regions processed and
sequenced in accordance with the methods and systems described
herein are full or partial exomes. These full or partial exomes can
be captured for sequencing using any methods known in the art,
including without limitation any of the Roche/NimbleGen exome
protocols, including the NimbleGen 2.1M Human Exome array and the
NimbleGen SeqCap EZ Exome Library, any of the Agilent SureSelect
products, any Illumina exome capture products, including the TruSeq
and Nextera Exome products, and any other products, methods,
systems and protocols known in the art.
[0093] In further embodiments, when the targeted regions of
interest comprise whole or portions of the exome, the baits used to
capture those targeted regions may be designed to be complementary
to those exonic sequences. In other embodiments, the baits are not
complementary to the exonic sequences themselves but are instead
complementary to sequences near the exonic sequence or to intronic
sequences between two exons. Such designs are also referred to
herein as "anchored exome capture" or "intronic baiting," by which,
as discussed herein, is meant a process in which one or more
portions of an exome are captured through the use of baits
complementary to one or more intronic sequences near or adjacent to
the one or more portions of the exome that are of interest. For
example, as schematically illustrated in FIG. 2, a genomic sequence
201 comprises exonic regions 202 and 203. Those exonic regions can
be captured by utilizing baits directed to one or more of the
intronic sequences nearby (for example intronic region 204 and/or
205 to capture exonic region 202 and intronic region 206 for
capture of exonic region 203). In other words, a population of
fragments comprising exonic regions 202 or 203 would be captured
through the use of baits complementary to intronic regions 204
and/or 205 and 206. In some embodiments, intronic baiting is used
to bridge exons separated by long intronic regions by sparsely
baiting longer introns. In such embodiments, the baits are not
necessarily targeting intronic regions that are close to the exonic
regions of interest, but the baits are instead designed to target
regions separated by particular distances (or sets of distances) or
are designed to tile across the intronic regions by a particular
number of bases or combinations of numbers of bases. Such
embodiments are described in further detail below.
[0094] In some embodiments, the intronic regions used for anchored
exome capture/intronic baiting techniques of the invention are
adjacent to the exonic region to be captured. In further
embodiments, the intronic regions are separated from the exonic
region to be captured by about 1-50, 2-45, 3-40, 4-35, 5-30, 6-25,
7-20, 8-15, 9-10, 2-20, 3-15, 4-10, 5-30, 10-40, 15-50, 20-75,
25-100 nucleotides. In still further embodiments, the intronic
regions are separated from the exonic regions to be captured by
about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 125, 150, 175,
200, 300, 400, or 500 nucleotides. In further embodiments,
particularly for situations in which sparse baiting of intronic
regions is of use (such as for phase variant detection or
identification of linked exonic regions across large intronic
distances) the intronic regions are separated from the exonic
regions to be captured by distances on the orders of kilobases,
e.g., 1-20, 2-18, 3-16, 4-14, 5-12, 6-10 kilobases. Since the
original molecular context of the enriched population of
oligonucleotides is retained, this sparse baiting of intronic
regions allows for the linking of sequence information between
exonic regions separated by long introns.
[0095] In further aspects, rather than designing the baits to
target particular regions of the genome, a tiling approach is used.
In such an approach, rather than targeting specific exonic or
intronic regions, the baits are instead designed to be
complementary to portions of the genome at particular ranges or
distances. For example, the library of baits can be designed to
hybridize to sequences located every 5 kilobases (kb) along the
genome, such that applying this library of baits to a fragmented
genomic sample will capture only a certain subset of the
genome--i.e., those regions that are contained in fragments
containing complementary sequences to the baits. As will be
appreciated, the baits can be designed based on a reference
sequence, such as a human genome reference sequence. In further
embodiments, the tiled library of baits is designed to capture
regions every 1, 2, 5, 10, 15, 20, 25, 50, 100, 200, 250, 500, 750,
1000, or 10000 kilobases of a genome. In some examples, this tiling
method has the effect of sparsely capturing intronic regions, thus
providing a way to link sequence information of exonic regions that
are separated by long intronic regions, because the original
molecular context of those exonic regions captured through sparse
capture of intronic regions is retained.
[0096] In still further embodiments, the baits are designed to tile
the genome in a random or combined manner--for example, a mixture
of tiled libraries can be used where some of the libraries capture
regions every 1 kb, whereas other libraries in the mixture capture
regions every 100 kb. In still further embodiments, the tiled
libraries are designed so that the baits target within a range of
positions within the genome--for example, the baits may target
regions of every 1-10, 2-5, 5-200, 10-175, 15-150, 20-125, 30-100,
40-75, 50-60 kb of the genome. In further examples, the tiled or
other capture methods described herein will capture about 5%, 10%,
15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% of the whole
genome. As will be appreciated, such tiling methods of capture will
capture both intronic and exonic regions of the genome for further
analysis such as sequencing.
[0097] In yet further embodiments and in accordance with any of the
methods described herein, the library of baits used in methods of
the present invention is a product of informed design that fulfills
one or more characteristics as further described herein. This
informed design includes instances in which the library of baits is
directed to informative single nucleotide polymorphisms (SNPs). As
discussed above, the term "informative SNPs" as used herein refers
to SNPs that are heterozygous. The library of baits in some
examples is designed to contain a plurality of probes that are
directed to regions of the genomic sample that contain informative
SNPs. By "directed to" as used herein is meant that the probes
contain sequences that are complementary to those regions of the
genomic sequences. Informed bait design provides the ability to
optimize targeted sequencing methods by allowing for targeted
enrichment with full coverage while at the same time reducing the
number of probes needed (and thus reducing costs and streamlining
the work flow).
[0098] In general, for methods utilizing informed bait design, the
libraries of baits are designed to include baits directed to
particular sequences in targeted regions of the genome based on the
presence or absence of informative SNPs in those regions and/or the
location(s) of those informative SNPs. An exemplary illustration of
general considerations for informed bait design is provided in FIG.
8. A region of the genome 801 can include exons (802 and 803). In
some examples, an informative SNP 804 will be located at the
boundary between the exon (802) and the adjacent intron. In such a
situation, the bait library can be designed to include probes
directed to one or more nucleotides (805) at a specified distance
away from the boundary. In further examples in which there is no
informative SNP at the boundary between the exon and the adjacent
intron (806), the bait library can be designed to include probes
directed to one or more positions in the intron near that boundary
(807 and 808). Those positions will preferably include informative
SNPs, but may also include other SNPs and/or other sequences as
needed. In still further examples in which an exon 803 contains an
informative SNP 809 in the interior of the exon but no informative
SNPs at the boundaries, the bait library can be designed to include
probes directed to several positions 810, 811, and 812 in the
adjacent intron that include a mixture of informative and
non-informative SNPs (as well as any other sequences as
needed).
[0099] In some aspects, one or more input characteristics are used
to design a probe bait library that is directed to shifting
locations along the genome based on those input characteristics as
well as map quality in various regions. This design is generally
based on spacing between informative SNPs rather than on the
locations of introns and exons. However, as will be appreciated,
any of the descriptions provided herein related to bait design
based on intron and exon locations can also be used in combination
with the informed bait design methods based on informative SNPs.
Input characteristics used in informed bait design include without
limitation and in any combination locations of exons, introns,
intergenic regions, informative SNPs, as well as regions of
repeating sequences (such as GC-rich regions), centromeres, and
sample nucleic acid lengths.
[0100] For ease of discussion, different characteristics of
informed design probe libraries are described below in terms of
different potential embodiments. As will be appreciated, any of the
probe libraries discussed herein, whether using any of the informed
design elements or any of the other types of design discussed above
can be used singly or in any combination. The design elements
utilized are selected based on the targeted genomic regions of
interest as well as sample input and the quality of mapping for
those regions of interest.
[0101] In some embodiments, probe bait libraries are designed to
include probes directed to regions that have a high likelihood of
containing informative SNPs in a given sample. Such targets may
include individual bases (the informative SNPs themselves) or one
or more bases that are proximal or adjacent to the informative
SNPs. In still further embodiments, the targets for the probe baits
may be directly adjacent to the informative SNPs or separated by
distances from about 1-200, 10-190, 20-180, 30-170, 40-160, 50-150,
60-140, 70-130, 80-120, 90-100 bases from an informative SNP.
[0102] In further embodiments, the probe bait libraries include
probes directed to regions of particular densities related to the
average length of the nucleic acid molecules. For example, the
probes can be designed to include probes at a density of target
sequences that is x-fold more dense than the average length of the
nucleic acid molecules/fragments to which the probes are
hybridizing, where x can be without limitation 1, 5, 10, 20, 50,
75, 100, 125, 150, or 200. Increasing the density of the probe
targets relative to the length of the nucleic acids increases the
ability to link probes across loci on the same physical molecule.
Such methods can also improve the probability that the linked
regions will include informative SNPs, thus further improving the
ability of the probe bait libraries to attach to targeted regions
of the genome.
[0103] The density of the probe targets may also be increased in
situations in which (at the population level) there is not a high
probability of informative SNPs in a given region of interest. In
such regions, tiling methods such as those described herein can be
used to direct probes at periodic spacings along the region. In
certain embodiments, the density of the spacing can be
differentially based, such that the density of probe spacing in
these regions lacking informative SNPs are at a 1, 2, 5, 10, 25,
50-fold shorter distance than probe spacing in regions containing
informative SNPs.
[0104] In further embodiments, the probe bait library is designed
to consider only informative SNP distribution within a gene
(including exons and introns). This method of design is directed to
capture a sufficient number of heterozygous SNPs at key locations
to link/phase from one end of the gene to the other. Such a design
method includes baits directed to sets of targets that combine
exonic informative SNPs with one or more non-exonic SNPs such that
the distance between informative SNPs in a gene is below the above
described densities of spacing.
[0105] Such informed design methods allow detection of not only
general targeted regions of the genome, but also allows the
detection and phasing of genomic structural variations, such as
translocations and gene fusions. By ensuring that any individual
gene can be phased, it follows that the vast majority of gene
fusion events can be detected and phased using the methods
described herein.
[0106] In certain embodiments and in accordance with any of the
above, the bait libraries are designed to target probes at
distances of about 1 kb to about 2 Mb. In further embodiments, the
distances are from about 1-50, 5-45, 10-40, 15-35, 20-30, 10-50
kb.
[0107] In further embodiments, the nucleic acid fragments being
targeted by the probe baits are from about 2 kb to about 250 Mb. In
still further embodiments, the fragments are from about 10-1000,
20-900, 30-800, 40-700, 50-600, 60-500, 70-400, 80-300, 90-200,
100-150, 50-500, 25-300 kb.
[0108] In some embodiments, the probe bait libraries are designed
such that about 60-95% of the probes hybridize to sequences
containing informative SNPs. In further embodiments, the probe bait
libraries are designed such that about 65%-85%, 70%-80%, 60-90%,
80-90%, 90-95%, 95%-99% of the probes in the library of probes are
designed to hybridize to informative SNPs. In still further
embodiments, at least 65%, 75%, 85%, 90%, 91%, 92%, 93%, 94%, 95%,
96%, 97% of the probes in the library of probes are designed to
hybridize to informative SNPs. As will be appreciated, for a probe
to be designed to "hybridize to" an informative SNP means that such
a probe hybridizes to a sequence region that includes that
informative SNP.
[0109] In further embodiments, the probe bait libraries are
designed to include a plurality of probes directed to informative
SNPs that are located within both exons and introns in targeted
portions of the genomic sample.
[0110] In still further embodiments, the libraries are designed
such that a majority of the probes in the library hybridize to
informative SNPs spaced apart by about 1-15, 5-10, 3-6 kb. In yet
further embodiments, the majority of the probes in the library of
probes are further designed to hybridize to informative SNPs spaced
apart by about 1, 3, 5, 10, 20, 30, 50 kb.
[0111] In further embodiments, a plurality of probes within the
library of probes are designed such that for targeted portions of
the genomic samples in which there are no informative SNPs within
5-300, 10-50, 20-100, 30-150, or 40-200 kb of boundaries between
exons and introns, the plurality of probes is designed to hybridize
at an informative SNP within an intron from those boundaries.
[0112] In further embodiments, a plurality of probes within the
library of probes are designed such that for targeted portions of
the genomic samples in which there is a first informative SNP
within an exon and that first informative SNP is located 5-300,
10-50, 20-100, 30-150, or 40-200 kb from a boundary with an
adjacent intron and a second informative SNP within the adjacent
intron and that second informative SNP is located 10-50 kb from the
boundary, the plurality of probes is designed to hybridize to a
region of the genomic sample between the first and second
informative SNPs;
[0113] In further embodiments, a plurality of probes within the
library of probes are designed such that for targeted portions of
the genomic samples comprising no informative SNPs for at least
5-300, 10-50, 20-100, 30-150, or 40-200 kb, the plurality of probes
is designed to hybridize every 0.5, 1, 3, or 5 kb to those targeted
portions of the genomic samples. In further embodiments, the
plurality of probes is designed to hybridize every 0.1, 0.5, 1,
1.5, 3, 5, 10, 15, 20, 30, 35, 40, 45, 50 kb along those targeted
portions of the genomic samples.
[0114] In further embodiments, a plurality of probes within the
library of probes are designed such that for targeted portions of
the genomic samples in which there are no informative SNPs within
5-300, 10-50, 20-100, 30-150, or 40-200 kb of boundaries between
exons and introns, the plurality of probes are designed to
hybridize to the next closest informative SNP to the exon-intron
boundaries.
[0115] In further embodiments, the library of probes comprises
probes designed to hybridize to regions of the genomic sample that
flank exons at a density that provides linkage information across
barcodes.
[0116] In still further embodiments, the range of coverage
represented by the library of probes is inversely proportional to
the distribution of lengths of the individual nucleic acid fragment
molecules of the genomic sample in the discrete partitions, such
that methods containing a higher proportion of longer individual
nucleic acid fragment molecules use libraries of probes with
smaller ranges of coverage.
[0117] In still further embodiments, the library of probes is
optimized for coverage of the targeted portions of the genomic
sample. In yet further embodiments, the density of coverage may be
lower for regions of high map quality, particularly for those
regions containing informative SNPs, and the density may further be
higher for regions of low map quality to ensure that linkage
information is provided across targeted regions.
[0118] In yet further embodiments, the library of probes has
features informed by characteristics of the one or more targeted
portions of a genomic sample, such that for targeted portions with
high map quality, the library of probes comprises probes that
hybridize to informative SNPs within 1 kb-1 Mb of boundaries of
exons and introns. The library of probes may in such situations
further include probes that hybridize to informative SNPs within
10-500, 20-450, 30-400, 40-350, 50-300, 60-250, 70-200, 80-150,
90-100 kb of boundaries of exons and introns.
[0119] In yet further embodiments, the library of probes has
features informed by characteristics of the one or more targeted
portions of a genomic sample, such that for targeted portions in
which the distribution of lengths of the barcoded fragments has a
high proportion of fragments longer than about 100, 150, 200, 250
kb, the library of probes comprise probes that hybridize to
informative SNPs separated by at least 50 kb. The library of probes
may in such situations further include probes that hybridize to
informative SNPs separated by at least 5, 10, 15, 20, 25, 30, 35,
40, 45, 50, 75, 100, 125, 150, 175, 200 kb.
[0120] In yet further embodiments, the library of probes has
features informed by characteristics of the one or more targeted
portions of a genomic sample, such that for targeted portions with
low map quality, the library of probes comprises probes that
hybridize to informative SNPs within 1 kb of exon-intron
boundaries. The library of probes may in such situations further
include probes that hybridize to informative SNPs within 2, 5, 10,
15, 20, 25, 30, 35, 40, 45, 50, 75, 100, 125, 150, 175, 200 kb of
exon-intron boundaries. In such situations, the library will
further include probes that hybridize and probes that hybridize to
informative SNPs within exons, within introns, or both.
[0121] In yet further embodiments, the library of probes has
features informed by characteristics of the one or more targeted
portions of a genomic sample, such that for targeted portions
comprising intergenic regions, the library of probes comprises
probes that hybridize to informative SNPs spaced apart at distances
of at least 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, 100
kb.
[0122] The baits used in the capture methods described herein can
be of any size or structure that is useful for enriching a
population of fragments for fragments containing targeted regions
of the genome. As discussed above, generally the baits of use in
the present invention comprise oligonucleotide probes that are
attached to a capture molecule, such as biotin. The oligonucleotide
probes may be complementary to sequences within a targeted region
of interest, or they may be complementary to regions outside of the
targeted region but close enough to that targeted region that both
the "anchoring" region and the targeted region are within the same
fragment, such that the bait is able to pull down the targeted
region by hybridizing to that nearby region (such as a flanking
intron).
[0123] The capture molecule attached to the bait may be any capture
molecule that can be used for isolating the bait and its
hybridization partner from other fragments in a population. In
general, the baits used herein are attached to biotin, and then
solid supports comprising streptavidin (including without
limitation magnetic streptavidin beads) can be used to capture the
baits and the fragments to which they are hybridized. Other capture
molecule pairs may include without limitation biotin/neutravidin,
antigen/antibody, or complementary oligonucleotide sequences.
[0124] In further embodiments, the oligonucleotide probe portion of
the baits can be of any length suitable for hybridizing to targeted
regions or to regions near targeted regions. In some embodiments,
the oligonucleotide probe portion of the baits used in accordance
with the methods described herein--i.e., the portion that
hybridizes to the targeted region of the genome or to a region near
the targeted region--generally has a length from about 10 to about
150 nucleotides in length (e.g., 35 nucleotides, 50 nucleotides,
100 nucleotides) and is chosen to specifically hybridize to a
target sequence of interest. In further embodiments, the
oligonucleotide probe portion comprises a length of about 5-10,
10-50, 20-100, 30-90, 40-80, 50-70, nucleotides in length. As will
be appreciated, any of the oligonucleotide probe portions described
herein may comprise RNA, DNA, non-natural nucleotides such as PNAs,
LNAs, and so on, or any combinations thereof.
[0125] An advantage of the methods and systems described herein is
that the targeted regions that are captured are processed prior to
capture in such a way that even after the steps of capturing the
targeted regions and conducting sequencing analyses, the original
molecular context of those targeted regions is retained. The
ability to attribute specific targeted regions to their original
molecular context (which can include the original chromosome or
chromosomal region from which they are derived and/or the location
of particular targeted regions in relation to each other within the
full genome) provides a way to obtain sequence information from
regions of the genome that are otherwise poorly mapped or have poor
coverage using traditional sequencing techniques.
[0126] For example, some genes possess long introns that are too
long to span using generally available sequencing techniques,
particularly using short-read technologies. Short-read technologies
are often preferable sequencing technologies, because they possess
superior accuracy as compared to long-read technologies. However,
generally used short-read technologies are unable to span across
long regions of the genome, and thus information may not be
obtainable using these conventional technologies in regions of the
genome that are difficult to characterize due to structural
characteristics such as long lengths of tandem repeating sequences,
high GC content, and exons containing long introns. In the methods
and systems described herein, however, the molecular context of
targeted regions is retained, generally through the tagging
procedure illustrated in FIG. 1 and described in further detail
herein. As such, links can be made across extended regions of the
genome. For example, as schematically illustrated in FIG. 2B,
nucleic acid molecule 207 contains two exons (shaded bars) with a
long intronic region (208). In the methods described herein, the
individual nucleic acid molecule 207 is distributed into its own
discrete partition 211 and then fragmented such that different
fragments contain different portions of the exons and the intron.
Because each of those fragments is tagged such that any sequence
information obtained from the fragments is then attributable to the
discrete partition in which it was generated, each fragment is thus
also attributable to the individual nucleic acid molecule 207 from
which it was derived.
[0127] In general, and as is described in further detail herein,
after fragmentation and tagging, fragments from different
partitions are combined together. Targeted capture methods can then
be used to enrich the population of fragments that undergoes
further analysis, such as sequencing, with fragments containing the
targeted region of interest. In the example illustrated in FIG. 2B,
the baits used will enrich the population of fragments to capture
only those containing a portion of the exons, but regions outside
of the exon and intron (such as 209 and 210) would not be captured.
Thus, the final population of fragments that undergoes sequencing
will be enriched for the fragments containing the portions of the
exons, even if those exons are separated by a long intronic region.
Short read, high accuracy sequencing technologies can then be used
to identify the sequences of this enriched population of fragments,
and because each of the fragments is tagged and thus attributable
to its original molecular context, i.e., its original individual
nucleic acid molecule, the short read sequences can be pieced
together to provide information about the relationship between the
exons. In some embodiments, the baits used to capture fragments
containing all or part of one or more exons are complementary to
one or more portions of the one or more exons themselves. In other
embodiments, the baits are complementary to one or more portions of
the intervening introns or to sequences adjacent to or near the
exon on either the 3' or 5' side of the exon regions (such baits
are also referred to herein as "intronic baits"). In further
embodiments, the baits used to capture the fragments containing all
or part of the exon include baits complementary to the exon itself
and intronic baits.
[0128] The ability to retain the molecular context of the targeted
regions captured for sequencing also provides the advantage of
allowing for sequencing across poorly characterized regions of the
genome. As will be appreciated, a significant percentage (at least
5-10% according to, for example Altemose et al., PLOS Computational
Biology, May 15, 2014, Vol. 10, Issue 5) of the human genome
remains unassembled, unmapped, and poorly characterized. The
reference assembly generally annotates these missing regions as
multi-megabase heterochromatic gaps, found primarily near
centromeres and on the short arms of the acrocentric chromosomes.
This missing fraction of the genome includes structural features
that remain resistant to accurate characterization using generally
used sequencing technologies. By providing the ability to link
information across extended regions of the genome, the methods
described herein provide a way to allow for sequencing across these
poorly characterized regions.
[0129] In some examples, sample preparation methods, including
methods of fragmenting, amplifying, partitioning, and otherwise
processing genomic DNA, can lead to biases or lower coverage of
certain regions of a genome. Such biases or lowered coverage can be
compensated for in the methods and systems disclosed herein by
altering the concentration of baits used to capture targeted
regions of the genome. For example, in some situations it is known
that certain regions of the genome will have low coverage after the
fragment library is processed, such as regions containing high GC
content or other structural variations that lead to bias toward
certain areas of the genome over others. In such situations, the
library of baits can be altered to increase the concentration of
baits directed to those regions of low coverage--in other words,
the population of baits used may be "spiked" to ensure that a
sufficient number of fragments containing targeted regions of the
genome in those low coverage areas are obtained in the final
population of fragments to be sequenced. Such spiking of baits may
be conducted through design of custom libraries in some
embodiments. In further embodiments, the spiking of baits can be
conducted in commercially available whole exome kits, such that a
custom library of baits directed toward the lower coverage regions
are added to off-the-shelf exome capture kits.
[0130] An advantage of the methods and systems described herein is
that the targeted regions that are captured are processed prior to
capture in such a way that even after the steps of capturing the
targeted regions and conducting sequencing analyses, the original
molecular context of those targeted regions is retained. As is
discussed in further detail herein, the ability to attribute
specific targeted regions to their original molecular context
(which can include the original chromosome or chromosomal region
from which they are derived and/or the location of particular
targeted regions in relation to each other within the full genome)
provides a way to obtain sequence information from regions of the
genome that are otherwise poorly mapped or have poor coverage using
traditional sequencing techniques.
[0131] For example, some genes possess long introns that are too
long to span using generally available sequencing techniques,
particularly using short-read technologies that possess superior
accuracy as compared to long-read technologies. In the methods and
systems described herein, however, the molecular context of
targeted regions is retained, generally through the tagging
procedure illustrated in FIG. 1 and described in further detail
herein. As such, links can be made across extended regions of the
genome. For example, as schematically illustrated in FIG. 2B,
nucleic acid molecule 207 contains exons (shaded bars) interrupted
by a long intronic region. Generally used sequencing technologies
would be unable to span the distance across the intron to provide
information on the relationship between the two exons. In the
methods described herein, the individual nucleic acid molecule 207
is distributed into its own discrete partition 209 and then
fragmented such that different fragments contain different portions
of the exons and the intron. Because each of those fragments is
tagged such that any sequence information obtained from the
fragments is then attributable to the discrete partition in which
it was generated, each fragment is thus also attributable to the
individual nucleic acid molecule 207 from which it was derived. In
general, and as is described in further detail herein, after
fragmentation and tagging, fragments from different partitions are
combined together. Targeted capture methods can then be used to
enrich the population of fragments that undergoes further analysis,
such as sequencing, with fragments containing the targeted region
of interest. In the example illustrated in FIG. 2B, the baits used
will enrich the population of fragments to capture only those
containing a portion of one of exons, but regions outside of the
exons (such as 209 and 210) would not be captured. Thus, the final
population of fragments that undergoes sequencing will be enriched
for the fragments containing the exons of interest. Short read,
high accuracy sequencing technologies can then be used to identify
the sequences of this enriched population of fragments, and because
each of the fragments is tagged and thus attributable to its
original molecular context, i.e., its original individual nucleic
acid molecule, the short read sequences can be pieced together to
span across the length of the intervening intron (which can in some
examples be on the order of 1, 2, 5, 10 or more kilobases in
length) to provide linked sequence information on the two
exons.
[0132] As noted above, the methods and systems described herein
provide individual molecular context for short sequence reads of
longer nucleic acids. As used herein, individual molecular context
refers to sequence context beyond the specific sequence read, e.g.,
relation to adjacent or proximal sequences, that are not included
within the sequence read itself, and as such, will typically be
such that they would not be included in whole or in part in a short
sequence read, e.g., a read of about 150 bases, or about 300 bases
for paired reads. In particularly preferred aspects, the methods
and systems provide long range sequence context for short sequence
reads. Such long range context includes relationship or linkage of
a given sequence read to sequence reads that are within a distance
of each other of longer than 1 kb, longer than 5 kb, longer than 10
kb, longer than 15 kb, longer than 20 kb, longer than 30 kb, longer
than 40 kb, longer than 50 kb, longer than 60 kb, longer than 70
kb, longer than 80 kb, longer than 90 kb or even longer than 100
kb, or longer. By providing longer range individual molecular
context, the methods and systems of the invention also provide much
longer inferred molecular context. Sequence context, as described
herein can include lower resolution context, e.g., from mapping the
short sequence reads to the individual longer molecules or contigs
of linked molecules, as well as the higher resolution sequence
context, e.g., from long range sequencing of large portions of the
longer individual molecules, e.g., having contiguous determined
sequences of individual molecules where such determined sequences
are longer than 1 kb, longer than 5 kb, longer than 10 kb, longer
than 15 kb, longer than 20 kb, longer than 30 kb, longer than 40
kb, longer than 50 kb, longer than 60 kb, longer than 70 kb, longer
than 80 kb, longer than 90 kb or even longer than 100 kb. As with
sequence context, the attribution of short sequences to longer
nucleic acids, e.g., both individual long nucleic acid molecules or
collections of linked nucleic acid molecules or contigs, may
include both mapping of short sequences against longer nucleic acid
stretches to provide high level sequence context, as well as
providing assembled sequences from the short sequences through
these longer nucleic acids.
IV. Samples
[0133] As will be appreciated, the methods and systems discussed
herein can be used to obtain targeted sequence information from any
type of genomic material. Such genomic material may be obtained
from a sample taken from a patient. Exemplary samples and types of
genomic material of use in the methods and systems discussed herein
include without limitation polynucleotides, nucleic acids,
oligonucleotides, circulating cell-free nucleic acid, circulating
tumor cell (CTC), nucleic acid fragments, nucleotides, DNA, RNA,
peptide polynucleotides, complementary DNA (cDNA), double stranded
DNA (dsDNA), single stranded DNA (ssDNA), plasmid DNA, cosmid DNA,
chromosomal DNA, genomic DNA (gDNA), viral DNA, bacterial DNA,
mtDNA (mitochondrial DNA), ribosomal RNA, cell-free DNA, cell free
fetal DNA (cffDNA), mRNA, rRNA, tRNA, nRNA, siRNA, snRNA, snoRNA,
scaRNA, microRNA, dsRNA, viral RNA, and the like. In summary, the
samples that are used may vary depending on the particular
processing needs.
[0134] Any substance that comprises nucleic acid may be the source
of a sample. The substance may be a fluid, e.g., a biological
fluid. A fluidic substance may include, but not limited to, blood,
cord blood, saliva, urine, sweat, serum, semen, vaginal fluid,
gastric and digestive fluid, spinal fluid, placental fluid, cavity
fluid, ocular fluid, serum, breast milk, lymphatic fluid, or
combinations thereof. The substance may be solid, for example, a
biological tissue. The substance may comprise normal healthy
tissues, diseased tissues, or a mix of healthy and diseased
tissues. In some cases, the substance may comprise tumors. Tumors
may be benign (non-cancer) or malignant (cancer). Non-limiting
examples of tumors may include: fibrosarcoma, myxosarcoma,
liposarcoma, chondrosarcoma, osteogenic sarcoma, chordoma,
angiosarcoma, endotheliosarcoma, lymphangiosarcoma,
lymphangioendotheliosarcoma, synovioma, mesothelioma, Ewing's,
leiomyosarcoma, rhabdomyosarcoma, gastrointestinal system
carcinomas, colon carcinoma, pancreatic cancer, breast cancer,
genitourinary system carcinomas, ovarian cancer, prostate cancer,
squamous cell carcinoma, basal cell carcinoma, adenocarcinoma,
sweat gland carcinoma, sebaceous gland carcinoma, papillary
carcinoma, papillary adenocarcinomas, cystadenocarcinoma, medullary
carcinoma, bronchogenic carcinoma, renal cell carcinoma, hepatoma,
bile duct carcinoma, choriocarcinoma, seminoma, embryonal
carcinoma, Wilms' tumor, cervical cancer, endocrine system
carcinomas, testicular tumor, lung carcinoma, small cell lung
carcinoma, non-small cell lung carcinoma, bladder carcinoma,
epithelial carcinoma, glioma, astrocytoma, medulloblastoma,
craniopharyngioma, ependymoma, pinealoma, hemangioblastoma,
acoustic neuroma, oligodendroglioma, meningioma, melanoma,
neuroblastoma, retinoblastoma, or combinations thereof. The
substance may be associated with various types of organs.
Non-limiting examples of organs may include brain, liver, lung,
kidney, prostate, ovary, spleen, lymph node (including tonsil),
thyroid, pancreas, heart, skeletal muscle, intestine, larynx,
esophagus, stomach, or combinations thereof. In some cases, the
substance may comprise a variety of cells, including but not
limited to: eukaryotic cells, prokaryotic cells, fungi cells, heart
cells, lung cells, kidney cells, liver cells, pancreas cells,
reproductive cells, stem cells, induced pluripotent stem cells,
gastrointestinal cells, blood cells, cancer cells, bacterial cells,
bacterial cells isolated from a human microbiome sample, etc. In
some cases, the substance may comprise contents of a cell, such as,
for example, the contents of a single cell or the contents of
multiple cells. Methods and systems for analyzing individual cells
are provided in, e.g., U.S. patent application Ser. No. 14/752,641,
filed Jun. 26, 2015, the full disclosure of which is hereby
incorporated by reference in its entirety, particularly all
teachings related to analyzing nucleic acids from individual
cells.
[0135] Samples may be obtained from various subjects. A subject may
be a living subject or a dead subject. Examples of subjects may
include, but not limited to, humans, mammals, non-human mammals,
rodents, amphibians, reptiles, canines, felines, bovines, equines,
goats, ovines, hens, avines, mice, rabbits, insects, slugs,
microbes, bacteria, parasites, or fish. In some cases, the subject
may be a patient who is having, suspected of having, or at a risk
of developing a disease or disorder. In some cases, the subject may
be a pregnant woman. In some case, the subject may be a normal
healthy pregnant woman. In some cases, the subject may be a
pregnant woman who is at a risking of carrying a baby with certain
birth defect.
[0136] A sample may be obtained from a subject by any means known
in the art. For example, a sample may be obtained from a subject
through accessing the circulatory system (e.g., intravenously or
intra-arterially via a syringe or other apparatus), collecting a
secreted biological sample (e.g., saliva, sputum urine, feces,
etc.), surgically (e.g., biopsy) acquiring a biological sample
(e.g., intra-operative samples, post-surgical samples, etc.),
swabbing (e.g., buccal swab, oropharyngeal swab), or pipetting.
[0137] While preferred embodiments of the present invention have
been shown and described herein, it will be obvious to those
skilled in the art that such embodiments are provided by way of
example only. Numerous variations, changes, and substitutions will
now occur to those skilled in the art without departing from the
invention. It should be understood that various alternatives to the
embodiments of the invention described herein may be employed in
practicing the invention. It is intended that the following claims
define the scope of the invention and that methods and structures
within the scope of these claims and their equivalents be covered
thereby.
EXAMPLES
Example 1
Whole Exome Capture and Sequencing: NA12878
[0138] Genomic DNA from the NA12878 human cell line was subjected
to size based separation of fragments using a Blue Pippin DNA
sizing system to recover fragments that were greater than or equal
to approximately 10 kb in length. The size selected sample nucleic
acids were then copartitioned with barcode beads in aqueous
droplets within a fluorinated oil continuous phase using a
microfluidic partitioning system (See, e.g., U.S. patent
application Ser. No. 14/682,952, filed Apr. 9, 2015, and
incorporated herein by reference in its entirety for all purposes),
where the aqueous droplets also included the dNTPs, thermostable
DNA polymerase and other reagents for carrying out amplification
within the droplets, as well as DTT for releasing the barcode
oligonucleotides from the beads. This was repeated both for 1 ng of
total input DNA and 2 ng of total input DNA. The barcode beads were
obtained as a subset of a stock library that represented barcode
diversity of over 700,000 different barcode sequences. The barcode
containing oligonucleotides included additional sequence components
and had the general structure: [0139] Bead-P5-BC-R1-Nmer
[0140] Where P5 and R1 refer to the IIlumina attachment and Read1
primer sequences, respectively, BC denotes the barcode portion of
the oligonucleotide, and Nmer denotes a random 10 base N-mer
priming sequence used to prime the template nucleic acids. See,
e.g., U.S. patent application Ser. No. 14/316,383, filed Jun. 26,
2014, the full disclosure of which is hereby incorporated herein by
reference in its entirety for all purposes.
[0141] Following bead dissolution, the droplets were thermocycled
to allow for primer extension of the barcode oligos against the
template of the sample nucleic acids within each droplet. This
resulted in amplified copy fragments of the sample nucleic acids
that included the barcode sequence representative of the
originating partition, in addition to the other included sequences
set forth above.
[0142] After barcode labeling of the copy fragments, the emulsion
of droplets including the amplified copy fragments was broken and
the additional sequencer required components, e.g., read2 primer
sequence and P7 attachment sequence, were added to the copy
fragments through an additional amplification step, which attached
these sequences to the other end of the copy fragments. The
barcoded DNA was then subjected to hybrid capture using an Agilent
SureSelect Exome capture kit.
[0143] The table below provides targeting statistics for the NA
12878 genome:
TABLE-US-00001 Median % Fragments % Bases Sample Insert Size on
Target on Target Version 1.A 258 81% 51% Version 1.B 224 81% 55%
Version 1.C 165 81% 63%
[0144] The three different versions listed above represent three
different shear lengths for the barcoded fragments before the
second adapter attachment step.
Example 2
Whole Exome Capture and Sequencing: NA19701 and NA19661
[0145] Genomic DNA from the NA19701 and NA19661 cell lines was
prepared according to the methods described above in Example 1.
Data, including phasing data, from those two cells lines is
provided in the table below:
TABLE-US-00002 NA19661 NA19701 N50_phase_block 29,535 83,953
N90_phase_block 8,595 25,584 mean_phase_block 5,968 21,128
median_phase_block 0 76.5 longest_phase_block 209,323 504,140
fract_genes_phased 0.719 0.841 fract_genes_completely_phased 0.679
0.778 fract_snps_phased 0.869 0.832 fract_snps_barcode 0.644 0.607
fract_snps_barcode_both_alleles 0.328 0.351
prob_snp_correct_in_gene 0.906 0.927 prob_snp_phased_in_gene 0.807
0.889 snp_short_switch_error 0.013 0.013 snp_long_switch_error
0.012 0.013
[0146] The present specification provides a complete description of
the methodologies, systems and/or structures and uses thereof in
example aspects of the presently-described technology. Although
various aspects of this technology have been described above with a
certain degree of particularity, or with reference to one or more
individual aspects, those skilled in the art could make numerous
alterations to the disclosed aspects without departing from the
spirit or scope of the technology hereof. Since many aspects can be
made without departing from the spirit and scope of the presently
described technology, the appropriate scope resides in the claims
hereinafter appended. Other aspects are therefore contemplated.
Furthermore, it should be understood that any operations may be
performed in any order, unless explicitly claimed otherwise or a
specific order is inherently necessitated by the claim language. It
is intended that all matter contained in the above description and
shown in the accompanying drawings shall be interpreted as
illustrative only of particular aspects and are not limiting to the
embodiments shown. Unless otherwise clear from the context or
expressly stated, any concentration values provided herein are
generally given in terms of admixture values or percentages without
regard to any conversion that occurs upon or following addition of
the particular component of the mixture. To the extent not already
expressly incorporated herein, all published references and patent
documents referred to in this disclosure are incorporated herein by
reference in their entirety for all purposes. Changes in detail or
structure may be made without departing from the basic elements of
the present technology as defined in the following claims.
* * * * *