U.S. patent application number 13/476736 was filed with the patent office on 2012-12-20 for nucleic acid amplification.
This patent application is currently assigned to LIFE TECHNOLOGIES CORPORATION. Invention is credited to Mark G. Erlander, Ranelle C. Salunga.
Application Number | 20120322113 13/476736 |
Document ID | / |
Family ID | 27370385 |
Filed Date | 2012-12-20 |
United States Patent
Application |
20120322113 |
Kind Code |
A1 |
Erlander; Mark G. ; et
al. |
December 20, 2012 |
NUCLEIC ACID AMPLIFICATION
Abstract
The present invention provides methods for the amplification of
nucleic acid molecules. Methods for amplifying target
polynucleotides, including mRNA, using oligonucleotides, DNA and
RNA polymerases are provided. The invention further provides
compositions and kits for practicing the methods, as well as
methods which use the amplification products.
Inventors: |
Erlander; Mark G.;
(Encinitas, CA) ; Salunga; Ranelle C.; (San Diego,
CA) |
Assignee: |
LIFE TECHNOLOGIES
CORPORATION
CARLSBAD
CA
|
Family ID: |
27370385 |
Appl. No.: |
13/476736 |
Filed: |
May 21, 2012 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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12819042 |
Jun 18, 2010 |
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13476736 |
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12610151 |
Oct 30, 2009 |
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12819042 |
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10942252 |
Sep 15, 2004 |
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12610151 |
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10062857 |
Oct 25, 2001 |
6794141 |
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10942252 |
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60298847 |
Jun 15, 2001 |
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60257801 |
Dec 22, 2000 |
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Current U.S.
Class: |
435/91.21 ;
435/91.51 |
Current CPC
Class: |
C12Q 1/6865 20130101;
C12N 15/1096 20130101; C12Q 1/6865 20130101; C12Q 1/686 20130101;
C12Q 2525/173 20130101; C12Q 2525/143 20130101 |
Class at
Publication: |
435/91.21 ;
435/91.51 |
International
Class: |
C12P 19/34 20060101
C12P019/34 |
Claims
1. A method of synthesizing a double stranded cDNA of an RNA
molecule for amplifying RNA sequences, said method comprising:
annealing an RNA molecule with a first oligonucleotide comprising a
primer operably linked to a promoter region to form a first
complex; synthesizing a first strand cDNA by reverse transcription
of said first complex to form hybrid(s) of RNA and first strand
cDNA; degrading first oligonucleotides not used in a) or b) above
with exonuclease activity; annealing said first strand cDNA, after
denaturing the hybrid(s) or degrading the RNA from said hybrid(s),
with a plurality of second oligonucleotides comprising a random
primer region to form a population of second complexes; forming
double stranded cDNA templates from said population of second
complexes with DNA polymerase activity; and transcribing the cDNA
templates with an RNA polymerase capable of initiating
transcription via the promoter region to produce amplified RNA
(aRNA).
2. The method of claim 1 wherein said RNA is mRNA.
3. The method of claim 1 wherein said RNA is part of a cellular
mRNA preparation.
4. The method of claim 2 wherein said first oligonucleotide
comprises a primer containing an oligo or poly dT sequence.
5. The method of claim 4 wherein said oligo or poly dT sequence is
at least, or about, eight dT in length.
6. The method of claim 1 wherein said random primer region
comprises at least, or about, six random nucleotides.
7. The method of claim 6 wherein said random primer region
comprises at least, or about, nine random nucleotides.
8. The method of claim 1 wherein said DNA polymerase activity is
DNA dependent.
9. The method of claim 8 wherein said DNA dependent polymerase
activity is selected from exonuclease deficient Klenow, Taq
polymerase activities, and combinations of exonuclease deficient
Klenow and/or Taq polymerase activities.
10. A method of amplifying RNA sequences complementary to, or
present in, one or more than one target polynucleotide that is
single stranded or made single stranded, comprising a) forming
double stranded cDNA templates containing sequences present in said
target polynucleotide, wherein said sequences are operably linked
to a promoter region, by i) annealing said one or more than one
single stranded target polynucleotide with a first oligonucleotide
comprising a primer operably linked to a promoter region to form a
first complex, ii) synthesizing one or more than one first strand
cDNA by reverse transcription of said first complex, iii) degrading
first oligonucleotides not used in i) or ii) above with exonuclease
activity, iv) annealing said one or more than one first stranded
cDNA, after denaturing the hybrid(s) of single stranded target
polynucleotide and cDNA or degrading the single stranded target
polynucleotide from said hybrid(s), with a plurality of second
oligonucleotides comprising a random primer region comprising at
least about six random nucleotides to form a population of second
complexes, and v) forming one or more than one double stranded cDNA
templates from said population of second complexes with DNA
dependent DNA polymerase activity; and b) transcribing said cDNA
templates with an RNA polymerase capable of initiating
transcription via said promoter region to produce amplified RNA
(aRNA) containing sequences complementary to said one or more than
one target polynucleotide; c) forming additional double stranded
DNA templates from said aRNA by i) annealing said aRNA with a third
oligonucleotide comprising a primer region operably linked to a
promoter region to form a third complex, ii) synthesizing the first
strand of said additional DNA template by reverse transcription of
said third complex to produce an aRNA/DNA hybrid, iii) annealing
said first strand of additional DNA template, after denaturing the
aRNA/DNA hybrid or degrading the aRNA from said hybrid, with said
first oligonucleotide to form a population of fourth complexes, and
iv) forming additional double stranded DNA templates from said
population of fourth complexes with DNA dependent DNA polymerase
activity; and d) transcribing said additional DNA templates with an
RNA polymerase capable of initiating transcription via the promoter
region of said first oligonucleotide to produce amplified RNA
(aRNA) containing sequences complementary to said target
polynucleotide or via the promoter region of said third
oligonucleotide to produce aRNA containing sequences present in
said target polynucleotide.
11. The method of claim 10 wherein said random primer region
comprises at least, or about, nine random nucleotides.
12. The method of claim 10 wherein said formation of additional
double stranded DNA templates from said aRNA further comprises
degrading third oligonucleotides not used in c) i) or c) ii) with
exonuclease activity before forming additional double stranded DNA
templates.
13. The method of claim 10 wherein said target polynucleotide is
mRNA.
14. The method of claim 10 wherein said more than one target
polynucleotide are a cellular mRNA preparation.
15. The method of claim 10 wherein said first oligonucleotide
comprises a primer containing an oligo or poly dT sequence.
16. The method of claim 15 wherein said oligo or poly dT sequence
is at least, or about eight dT in length
17. The method of claim 10 wherein said DNA dependent DNA
polymerase activity is selected from exonuclease deficient Klenow,
Taq polymerase activities, and combinations of exonuclease
deficient Klenow and/or Taq polymerase activities.
18. The method of claim 10 wherein said formation of additional
double stranded DNA templates from said aRNA further comprises
degrading third oligonucleotides not used in c) i) or c) ii) with
exonuclease activity before forming additional double stranded DNA
templates.
19. The method of claim 10 wherein said third oligonucleotide
comprises a known primer sequence or a random primer region of at
least about six random nucleotides or at least about nine random
nucleotides.
20. The method of claim 10 wherein said first oligonucleotide
comprises a T7 promoter region and said third oligonucleotide
optionally comprises a T3 or SP6 promoter region.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The technical field of this invention is enzymatic
amplification of nucleic acids. More particularly, the invention
provides methods, compositions and kits relating to amplifying
(i.e., making multiple copies of) target polynucleotides to produce
multiple copies thereof. The multiple copies may contain either the
sense or antisense sequence of the amplified target polynucleotide.
The invention also provides amplification of target
polynucleotides, even if present in limited quantities, fbr use in
subsequent analytical or preparative purposes.
BACKGROUND
[0002] Differential expression analysis of mRNA species in a test
population requires the quantitative determination of different
mRNA levels in the population. Although detection of a nucleic acid
and its sequence analysis can be carried out by probe
hybridization, the method generally lacks sensitivity when amounts
of target nucleic acid in the test sample are low. Low copy number
nucleic acid targets are difficult to detect even when using highly
sensitive reporter groups like enzymes, fluorophores and
radioisotopes. Detection of rare mRNA species is also complicated
by factors such as heterogeneous cell populations, paucity of
material, and the limits of detection of the assay method. Methods
which amplify heterogeneous populations of mRNA also raise concerns
with introduction of significant changes in the relative amounts of
different mRNA species.
[0003] Applications of nucleic acid amplification method include
detection of rare cells, pathogens, altered gene expression in
malignancy, and the like. Nucleic acid amplification is potentially
useful for both qualitative analysis, such as the detection of
nucleic acids present in low levels, as well as the quantification
of expressed genes. The latter is particularly useful for
assessment of pathogenic sequences as well as for the determination
of gene multiplication or deletion associated with malignant cell
transformation. A number of methods for the amplification of
nucleic acids have been described, e.g., exponential amplification,
linked linear amplification, ligation-based amplification, and
transcription-based amplification. An example of exponential
nucleic acid amplification method is polymerase chain reaction
(PCR) which has been disclosed in numerous publications. (see
Mullis et al. Cold Spring Harbor Symp. Quant. Biol. 51:263-273
(1986); PCR Cloning Protocols: From Molecular Cloning to Genetic
Engineering, Methods in Molecular Biology, White, B. A., ed., vol.
67 (1998); Mullis EP 201,184; Mullis et al., U.S. Pat. Nos.
4,582,788 and 4,683,195; Erlich et al., EP 50,424, EP 84,796, EP
258,017, EP 237,362; and Saiki R. et al., U.S. Pat. No. 4,683,194).
Linked linear amplification is disclosed by Wallace et al. in U.S.
Pat. No. 6,027,923. Examples of ligation-based amplification are
the ligation amplification reaction (LAR), disclosed by Wu et al.
in Genomics 4:560 (1989) and the ligase chain reaction, disclosed
in EP Application No. 0320308 B1. Hampson et al. (Nucl. Acids Res.
24(23):4832-4835, 1996) describe a directional random
oligonucleotide primed (DROP) method for use as part of global PCR
amplification.
[0004] Isothermal target amplification methods include
transcription-based amplification methods, in which an RNA
polymerase promoter sequence is incorporated into primer extension
products at an early stage of the amplification (WO 89/01050), and
a target sequence or its complement is amplified by transcription
and digestion of the RNA strand in a DNA/RNA hybrid intermediate.
(See, for example, U.S. Pat. Nos. 5,169,766 and 4,786,600). These
methods include transcription mediated amplification (TMA),
self-sustained sequence replication (3SR), Nucleic Acid Sequence
Based Amplification (NASBA), and variations thereof. (See Guatelli
et al. Proc. Natl. Acad. Sci. U.S.A. 87:1874-1878 (1990); U.S. Pat.
Nos. 5,766,849 (TMA); and 5,654,142 (NASBA)).
[0005] Some transcription-based amplification methods (Malek et
al., U.S. Pat. No. 5,130,238; Kacian and Fultz, U.S. Pat. No.
5,399,491; Burg et al., U.S. Pat. No. 5,437,990) use
primer-dependent nucleic acid synthesis to generate a DNA or RNA
product, which serves as a template for additional rounds of
primer-dependent nucleic acid synthesis. These methods use at least
two primers each having sequences complementary to different
strands of a target nucleic acid sequence and results in an
exponential amplification of the number of copies of the target
sequence. However, these methods are not amenable for global gene
expression monitoring applications.
[0006] Amplification methods that utilize a single primer are also
useful for amplification of heterogeneous mRNA populations. Since
the vast majority of mRNAs comprise a homopolymer of 20-250
adenosine residues on their 3' ends (the poly-A tail), poly-dT
primers can be used for cDNA synthesis. "Single-primer
amplification" protocols utilize a single primer containing an RNA
polymerase promoter sequence and a sequence, such as oligo-dT,
complementary to the 3'-end of the desired nucleic acid target
sequence(s) ("promoter-primer"). (Kacian et al., U.S. Pat. No.
5,554,516; van Gelder et al., U.S. Pat. Nos. 5,545,522 ('522),
5,716,785 ('785) and 5,891,636 ('636)). These methods use, or could
be adapted to use, a primer containing poly-dT for amplification of
heterogeneous mRNA populations. In methods described in '522, '785
and '636, the promoter-primer is used to prime the synthesis of a
first strand and an endogenously derived primer is used for second
strand synthesis. The double-stranded cDNA thus generated includes
a promoter coupled to a sequence corresponding to the target RNA
and is used as a template for the synthesis of multiple copies of
RNA complementary to the target sequence(s) ("antisense RNA") by
use of RNA polymerase. The method described in U.S. Pat. No.
5,716,785 has been used to amplify cellular mRNA for monitoring
gene expression (e.g., van Gelder et al. (1990), Proc. Natl. Acad.
Sci. USA 87, 1663; Lockhart et al. (1996), Nature Biotechnol. 14,
1675).
[0007] Another method to produce "antisense RNA" with an RNA
polymerase is disclosed by Loewy (U.S. Pat. No. 5,914,229) where a
single-stranded nucleic acid of interest is combined with an
oligonucleotide containing a double stranded promoter and a single
stranded segment complementary to the nucleic acid of interest.
Eberwine (BioTechniques 20:584-591 (1996)) disclose yet another
means to amplify mRNA and produce "antisense RNA" by using
immobilized oligo(dT)-T7 primers to produce the necessary cDNA.
Wang et al. (U.S. Pat. No. 5,932,541) disclose the use of a
"captureable" primer to produce the first strand of a cDNA before
it is immobilized on a solid support (via the "capturable primer)
prior to the synthesis of the second cDNA strand.
[0008] Another in vitro transcription protocol is disclosed by
Hughes et al. (Nature Biotech. 19:342-347, April 2001), where a two
primer system (modified from U.S. Pat. No. 6,132,997) and an
adapted PCR coupled system are used.
SUMMARY OF THE INVENTION
[0009] The present invention provides methods, compositions and
kits relating to amplifying target polynucleotides and generating
amplified RNA (aRNA). Optionally, each aRNA contains known, or
"anchor", sequences at the 5' and/or 3' ends. Anchor sequences may
be used for the following: to generate sense amplified RNA and/or
antisense amplified RNA (given RNAs that are flanked by T7 and T3
promoter sequences), to enhance second strand synthesis in the
second round, and as primer sites for PCR amplification of
normalized cDNA (see example 2 below). The aRNA may be in the form
of either a "sense" RNA molecule containing all or part of the
sequence found in the target polynucleotide, or an "antisense" RNA
molecule containing a sequence complementary to all or part of the
sequence found in the target polynucleotide, and may also include
the optional anchor sequences.
[0010] In one aspect of the invention, a double stranded DNA
molecule is produced to contain all or part of the sequence of the
target polynucleotide of interest as well as one or more promoters
capable of initiating the transcription of either strand of the
double stranded DNA. The production of the double stranded DNA
begins with the initial production of a first strand, "antisense"
DNA by hybridizing a strand of the target polynucleotide with a
first oligonucleotide comprising a first primer region containing a
sequence complementary to a sequence at or near the 3' end of the
target polynucleotide and a RNA polymerase promoter region coupled
to the 5' end of the first primer region. If the target
polynucleotide is single stranded, it may be used directly. If the
target polynucleotide is double stranded, it is first denatured to
generate a single stranded target polynucleotide. The single
stranded target polynucleotide is used as the template for the
production of said first strand DNA. Optionally, the first primer
region and the promoter region is separated by a known, or
"anchor", sequence. Moreover, the promoter region is optionally
relatively unhybridizable to the polynucleotide template.
[0011] After said hybridizing event, a first strand DNA
complementary to the target polynucleotide is produced by extending
the first oligonucleotide. Where the target polynucleotide used as
the template is a single stranded RNA molecule, enzymatic extension
of the first oligonucleotide with reverse transcriptase activity
may be used. As an optional, but preferred embodiment of the
invention, excess or residual first oligonucleotides not used to
prime first strand DNA molecules are degraded. After production of
the first strand DNA, it is separated from the target
polynucleotide template, and one or more second oligonucleotides
are hybridized to the first strand DNA. This may be accomplished by
heating the reaction components, which also terminates reverse
transcriptase activity.
[0012] The one or more second oligonucleotide contain a second
primer region containing sequences which are complementary to all
or part of the first strand DNA to permit hybridization to occur.
The second primer regions may contain, or be, random sequences of
various lengths, such that hybridization may occur at various
sequences along the length of the first strand DNA. Alternatively,
the second primer regions may contain one or more known sequences,
complementary to sequences on the first strand DNA, such that the
one or more second oligonucleotides will hybridize at known
positions along the first strand DNA. Preferably, the known
sequences used in the second primer region are complementary to a
sequence at or near the 3' end of the first strand DNA or at least
located at some distance from the 5' end of the first strand
DNA.
[0013] The second oligonucleotide may optionally further contain a
second known, or "anchor", sequence coupled to the 5' end of the
second primer region. In another optional embodiment of the second
oligonucleotide, a second promoter may be coupled either to the 5'
end of the second primer region or to the 5' end of the "anchor"
sequence.
[0014] After hybridization of the second oligonucleotide, a double
stranded DNA is produced by forming a second strand DNA, by primer
extension, that is complementary to all or part of the first strand
DNA. Due to the first strand DNA being produced via the use of a
promoter-containing first oligonucleotide, the resultant double
stranded DNA has a promoter region coupled to an end of the double
stranded DNA corresponding to the 5' end of the first strand DNA.
The first oligonucleotide is preferably designed to permit the
promoter region to initiate transcription that produces RNA
containing all or part of the first primer region and any optional
"anchor" sequence present in the first oligonucleotide.
[0015] In another aspect of the invention, and after production of
the double stranded DNA, the promoter is contacted with an RNA
polymerase capable of initiating transcription from the promoter to
transcribe one or more copies of an amplified RNA (aRNA)
complementary to sequences present on the second strand DNA.
Preferably, the aRNA comprises in a 5' to 3' order, the optionally
present "anchor" sequence, the first primer sequence, a sequence
complementary to all or part of the target polynucleotide, and a
sequence complementary to the second oligonucleotide. The resultant
aRNA would thus be "antisense" relative to the target
polynucleotide of interest.
[0016] The above discussion may also be viewed as "round one" of
the nucleic acid amplification provided by the present
invention.
[0017] In another aspect of the invention, "round two"
amplification is provided to enable further amplification of
"antisense" aRNA as well as "sense" aRNA. Round two amplification
is possible by using the above aRNA to produce multiple copies of
double stranded DNA constructs to further amplify the target
polynucleotide. In round two, the above aRNA is used to first
produce another first strand DNA. This starts by hybridizing the
above aRNA to one or more "round one" second oligonucleotides as
described above. This round two first strand DNA is produced upon
extension of the second oligonucleotide(s) with reverse
transcriptase activity, with the above aRNA acting as the template.
After production of the round two first strand DNA, it is separated
from the aRNA template and hybridized with the "round one" first
oligonucleotide as described above. Extension of the first
oligonucleotide produces a round two second strand DNA, and
simultaneous extension of the round two first strand DNA at its 3'
end, to be fully complementary to the first oligonucleotide,
results in the round two double stranded DNA molecule. This round
two double stranded DNA molecule contains a promoter region,
present via the first oligonucleotide, that is coupled to an end
corresponding to the 5' end of the round two second strand DNA.
Thus initiation of transcription from the promoter region results
in production of one or more copies of round two aRNA, which
contain sequences of the "round one" aRNA. Preferably, this round
two aRNA comprises in a 5' to 3' order, the optionally present
"anchor" sequence and the first primer sequence (from the "round
one" first oligonucleotide), a sequence complementary to all or
part of the original target polynucleotide, and a sequence
complementary to the second oligonucleotide(s) used. The resultant
aRNA would again be "antisense" relative to the original target
polynucleotide of interest.
[0018] Use of round two permits significant further amplification
of the target polynucleotide because the quantity of "round one"
aRNA is used to prepare multiple round two double stranded DNAs
which may then used to produce even larger amounts of aRNA upon
transcription.
[0019] In further embodiments of round two, the second
oligonucleotide(s) used to generate the round two first strand DNA
can be used to affect the form of round two aRNA. In one
embodiment, and consistent with its description in "round one", the
second oligonucleotides contain second primer regions containing
random sequences such that the second oligonucleotide hybridizes to
various sequences along the length of the "round one" aRNA. As
such, the resultant double stranded DNA permits round two
transcription to produce aRNA containing all or part, depending on
where hybridization occurs, of the sequences of the "round one"
aRNA that are complementary to the original target polynucleotide.
Of course the second oligonucleotide may still optionally contain
"anchor" sequences linked to the 5' end.
[0020] In another embodiment of round two, the second
oligonucleotide(s) contain second primer regions that contain one
or more known sequences, complementary to sequences on the "round
one" aRNA. Thus, the second oligonucleotide(s) will hybridize at
known position(s) along the aRNA. If hybridization occurs at the 3'
end of the aRNA, then the resultant double stranded DNA permits
round two transcription to produce aRNA identical to "round one"
aRNA. If the second oligonucleotide(s) hybridize internally within
the aRNA template, the resultant double stranded DNA permits round
two transcription to produce aRNA containing part of the sequences
of the "round one" aRNA that are complementary to the original
target polynucleotide. Of course the second oligonucleotide may
still optionally contain "anchor" sequences linked to the 5'
end.
[0021] In both of the above embodiments of round two, the second
oligonucleotide(s) used may, as described for "round one",
optionally contain a promoter region directly or indirectly coupled
to the 5' end of the second primer region. Extension of the second
oligonucleotide, followed by priming and extension with the "round
one" first oligonucleotide, results in a double stranded DNA
molecule wherein both strands can serve as a template for
transcription initiated from either the promoter coupled to the
second oligonucleotide and/or the promoter coupled to the "round
one" first oligonucleotide. This possible embodiment permits
additional alternatives for the practice of round two.
[0022] In one alternative embodiment, the promoter region present
in the second oligonucleotide(s) is different from the promoter
present in the first oligonucleotide (of round one or round two).
This results in the double stranded DNA containing promoter regions
at both ends of the molecule, such that initiation of transcription
from the promoter region present via the first oligonucleotide
results in the production of aRNA complementary (or "antisense") to
the original target polynucleotide, while initiation of
transcription from the promoter region present via the second
oligonucleotide results in the production of aRNA containing
sequences of the original target polynucleotide. The latter aRNA
are thus "sense" relative to the original target
polynucleotide.
[0023] In a further alternative embodiment of round two, a slightly
different double stranded DNA is produced. This starts by
hybridizing "round one" aRNA with a second oligonucleotide (as
described for "round one") that contains a promoter region as
described above. After production of the round two first strand DNA
and separation away from the aRNA template, the round two first
strand DNA is hybridized with an oligonucleotide which does not
contain a promoter region. As such, the round two second strand DNA
may be produced by extension of an oligonucleotide as described
above for the "round one" first oligonucleotide except that it does
not contain a promoter region or instead of this "round one" first
oligonucleotide that is promoter-less, one could use a random
primer for subsequent extension. Extension to produce the round two
second strand DNA includes a sequence complementary to the primer
region (containing the promoter region) of the second
oligonucleotide and this occurs simultaneously with the extension
of the round two first strand DNA at its 3' end to be fully
complementary to the promoter-free oligonucleotide primer. The
resultant round two double stranded DNA molecule would thus only
contain a promoter region, present via the second oligonucleotide
used for extension of the first strand DNA, that is coupled to an
end corresponding to the 5' end of the round two first strand DNA.
Thus initiation of transcription from the promoter region results
in production of one or more copies of round two aRNA which contain
sequences complementary to all or part of "round one" aRNA. Stated
differently, this type of round two aRNA would contain all or part
of the sequences of the original target polynucleotide. As such,
the aRNA is "sense" relative to the original target polynucleotide.
Preferably, this type of round two aRNA comprises in a 5' to 3'
order, the optionally present "anchor" sequence and the second
primer sequence from the round two second oligonucleotide, the
sequence of all or part of the original target polynucleotide, and
a sequence complementary to the promoter-free oligonucleotide
used.
[0024] It should be noted that in all of the above methods,
"exogenous primers" are present at least in the form of the
oligonucleotides used to prime synthesis of the second DNA strand
in "round one" or the first DNA strand in round two.
[0025] The methods of the present invention may be used to detect a
RNA molecule of interest from a cell or organism. Preferably the
cell is a eukaryotic or human cell, more preferred are cells from
malignant cells, such as those associated with cancer, especially
breast cancer. The present methods may be used to amplify one mRNA
from the entire population of mRNAs in a given
cell/tissue/organism. In preferred embodiments of the invention,
the entire mRNA population from one or more than one cell that is
laser-captured (laser capture microdissection) from fixed tissues
from model organisms of human diseases or actual human tissue
(postmortem or biopsy material) is amplified. More than one cell
includes a plurality or other multitude of cells, from a cell
culture or a tissue or cell type therein. Cells that may be used in
the practice of the present invention include, but are not limited
to, primary cells, cultured cells, tumor cells, non-tumor cells,
blood cells, cells of the pituitary or other endocrine glands, bone
cells, lymph node cells, brain cells, lung cells, heart cells,
spleen cells, liver cells, kidney cells, and vascular tissue
cells.
[0026] Beyond cancer cells, the present invention may be applied to
tissues (and cell types therein) involved in, or associated with,
any disease or undesired condition. For example, and without
limiting the invention, the present invention may be used to
determine gene expression in neuronal and non-neuronal cells
involved in disorders of the nervous system, such as, but not
limited to, neurodegenerative diseases, including Parkinson's
disease and Alzheimer's disease; multiple sclerosis; and
psychiatric disorders, including schizophrenia and affective
disorders such as manic depression, lack of apetitite control, and
attention deficit disorder. Expressed nucleic acids from different
neuronal cell types involved in or associated with the above
disorders, either by single or multiple cells of the same type or
subtype, may be amplified with the present invention for further
characterization. Similarly, expressed nucleic acids from
non-neuronal cells associated with such disorders (including, but
not limited to microglial cells, astrocytes, oligodendricytes, and
infiltrating inflammatory cells) may also be amplified with the
present invention.
[0027] Also without limiting the invention, expressed nucleic acids
from cells associated with disorders of the cardiovascular and
urinary systems may be amplified with the present invention.
Examples from the area of cardiovascular disease include, but are
not limited to, smooth muscle cells, endothelial cells and
macrophages while examples from kidney disorders include, but are
not limited to, cells of the cortex, medulla, glomerulus, proximal
and distal tubules, Bowman's capsule and the Loop of Henley.
[0028] Inflammatory and autoimmune diseases are additional
non-limiting examples of disorders wherein the tissues and cells
involved in or associated therewith may be used in combination with
the present invention. Examples of such disorders include
rheumatoid arthritis, myasthenia gravis, lupus erythematosus,
certain types of anemia, multiple sclerosis, and juvenile-onset
diabetes. Cells involved in such diseases include neutrophils,
eosinophils, basophils, monocytes, macrophages, lymphocytes,
[0029] Additional examples of cancer cells which may be used in
conjunction with the present invention include, but are not limited
to, cells from sarcomas, carcinomas, lymphomas, leukemias, prostate
cancer, lung cancer, colorectal cancer, soft tissue cancers,
biopsies, skin cancer, brain cancer, liver cancer, ovarian cancer,
and pancreatic cancer. Kits containing one or more components, such
as the primers or polymerases of the invention, optionally with an
identifying description or label or instructions relating to their
use in the methods of the present invention are also provided by
the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is an illustration of one exemplary embodiment using
a single stranded RNA as the target polynucleotide. Generally, RT
refers to reverse transcriptase; heat kill refers to termination of
RT activity; exonuclease treatment is an optional additional step
to remove excess primer; and denaturation refers to the separation
of the first strand DNA from the target polynucleotide. With
respect to "round one", the use of random nonamers, exonuclease
minus Klenow and Taq polymerase (thermal stable DNA polymerase from
Thermus aquaticus), a T7 promoter, and an optional A1 "anchor"
sequence reflect just one possible embodiment of the invention.
With respect to "round two modified", the use of a T3 promoter
containing primer reflects just one possible embodiment of the
invention.
[0031] FIGS. 2A-2C show the results of a test comparing the
synthesis of "round one" second strand in accordance with different
embodiments of the invention as well as comparison to "endogenous
priming" conditions without the use of exogenous primers. FIG. 2A
shows the results of gel electrophoresis analysis of aRNA via
different second strand syntheses. Each set of conditions was
conducted in duplicate. FIG. 2B shows the yields of amplified RNA
(aRNA) for each of the conditions tested. FIG. 2C shows a
comparison of the yields with the fold amplification.
[0032] FIGS. 3A and 3B show the successful results of amplifying
small amounts of total RNA (2 ng and 10 ng of total RNA extracted
from mouse brain). These results demonstrate that very small
quantities of mRNA can be amplified.
DETAILED DESCRIPTION OF THE INVENTION
A. Definitions
[0033] A "polynucleotide" is a polymeric form of nucleotides of any
length, either ribonucleotides or deoxyribonucleotides. This term
refers only to the primary structure of the molecule. Thus, this
term includes double- and single-stranded DNA and RNA. It also
includes known types of modifications including labels known in the
art, methylation, "caps", substitution of one or more of the
naturally occurring nucleotides with an analog, and internucleotide
modifications such as uncharged linkages (e.g., phosphorothioates,
phosphorodithioates, etc.), appendant moieties (including proteins
such as nucleases, toxins, antibodies, signal peptides,
poly-L-lysine, etc.), intercalators (e.g., acridine, psoralen,
etc.), chelators (e.g., metals, radioactive metals, etc.),
alkylators, modified linkages (e.g., alpha anomeric nucleic acids,
etc.), as well as unmodified forms of the polynucleotide.
[0034] A "target polynucleotide" or "target sequence," as used
herein, contains a polynucleotide sequence of interest, for which
amplification is desired. The target sequence may be known or not
known, in terms of its actual sequence. Generally, a "template," as
used herein, is a polynucleotide that contains the target
polynucleotide sequence. In some instances, the terms "target
sequence," "template DNA," "template polynucleotide," "target
nucleic acid," "target polynucleotide," and variations thereof, are
used interchangeably.
[0035] The primer regions containing known sequences, as used
herein, are selected to be "substantially" complementary to each
specific sequence to be amplified, i.e.; the primers should be
sufficiently complementary to hybridize to their respective
targets. Therefore, the primer sequence need not reflect the exact
sequence of the target, and can, in fact be "degenerate."
Non-complementary bases or longer sequences can be interspersed
into the primer, provided that the primer sequence has sufficient
complementarity with the sequence of the target to be amplified to
permit hybridization and extension.
[0036] Primer regions containing random sequences, as used herein,
are not necessarily known to be complementary to target sequences
to be amplified, but preferably include sequences that are
sufficiently complementary to target sequences to permit primer
extension reactions to occur via polymerase activity. Primers may
be of any length suitable for hybridization and primer extension
under the conditions used. As noted above, primers may be random
such that they contain heterologous sequences. Primers heterologous
in lengths may also be used in the practice of the invention.
Primers may be DNA, RNA or a chimeric combination thereof in
structure. Preferred random primer lengths are from about four
nucleotides to about 10 nucleotides. Even more preferred are random
primers of nine or about nine nucleotides in length. Primers of
known sequences may be of lengths from about 12 to about 50 to 100
nucleotides in length. The term "amplify" is used in the broad
sense to mean creating an amplification product which may include,
for example, additional target molecules, or target-like molecules
or molecules complementary to the target molecule, which molecules
are created by virtue of the presence of the target molecule in the
sample. In the situation where the target is a nucleic acid, an
amplification product can be made enzymatically with RNA
polymerases with the involvement of DNA polymerases in generating
double stranded DNA. "Amplification," as used herein, generally
refers to the process of producing multiple copies of a desired
sequence. "Multiple copies" mean at least 2 copies. A "copy" does
not necessarily mean perfect sequence complementarity or identity
to the template sequence. For example, copies can include
nucleotide analogs such as deoxyinosine, intentional sequence
alterations (such as sequence alterations introduced through a
primer comprising a sequence that is hybridizable, but not
complementary, to the template), and/or sequence errors that occur
during amplification.
[0037] The present invention also provides methods for amplifying
mRNA. As such, the subject invention provides methods of producing
amplified amounts of RNA from a starting target mRNA. By amplified
amounts is meant that for each starting mRNA, multiple
corresponding amplified RNAs (aRNAs) are produced where the
amplified RNA has a sequence identical to or complementary to the
initial mRNA. By corresponding is meant that the aRNA shares a
substantial amount of sequence identity with the starting mRNA or
its complement. Substantial amount means at least 95%, usually at
least 98% and more usually at least 99%, and sequence identity is
determined using the BLAST algorithm, as described in Altschul et
al. (1990), J. Mol. Biol. 215:403-410 (using the published default
setting, i.e. parameters w=4, t=17). Generally, the number of
corresponding aRNA molecules produced for each starting mRNA during
the linear amplification methods will be at least about 10, usually
at least about 50 and more usually at least about 100, where the
number may be as great as 600 or greater, but often does not exceed
about 5000. Fold amplification of mRNAs by the present invention is
from about 1000 fold per round to about 5000 fold per round. As
used herein, the term "anchor" or "anchor sequence" refers to a
specific nucleic acid sequence that may serve to identify a batch
of polynucleotides containing said sequence therein.
Polynucleotides from the same biological source are covalently
"anchored" with a specific sequence so that in subsequent analysis
the polynucleotide can be identified according to its source of
origin. The sequence "anchors" may also serve as all or part of the
primer regions as disclosed herein. Alternatively, the "anchors"
may serve simply to link primer regions to promoter regions as
disclosed herein. While the use of anchor sequences is fully within
the scope of the present invention, an additional aspect of the
invention is the unexpected discovery that the non-inclusion of an
anchor sequence may result in improved production of cDNAs and
aRNAs when compared to conditions including the use of an anchor
sequence.
[0038] A "microarray" is a linear or two-dimensional array of
preferably discrete regions, each having a defined area, formed on
the surface of a solid support. The density of the discrete regions
on a microarray is determined by the total numbers of target
polynucleotides to be detected on the surface of a single solid
phase support, preferably at least about 50/cm.sup.2, more
preferably at least about 100/cm.sup.2, even more preferably at
least about 500/cm.sup.2, and still more preferably at least about
1,000/cm.sup.2. As used herein, a DNA microarray is an array of
oligonucleotide primers or cDNAs placed on a chip or other
surfaces. Since the position of each particular group of primers or
cDNAs in the array is known, the identities of the target
polynucleotides can be determined based on their binding to a
particular position in the microarray.
[0039] The term "label" refers to a composition capable of
producing a detectable signal indicative of the presence of the
target polynucleotide in an assay sample. Suitable labels include
radioisotopes, nucleotide chromophores, enzymes, substrates,
fluorescent molecules, chemiluminescent moieties, magnetic
particles, bioluminescent moieties, and the like. As such, a label
is any composition detectable by spectroscopic, photochemical,
biochemical, immunochemical, electrical, optical or chemical
means.
[0040] The term "support" refers to conventional supports such as
beads, particles, dipsticks, fibers, filters, membranes and silane
or silicate supports such as glass slides.
[0041] As used herein, a "biological sample" refers to a sample of
tissue or fluid isolated from an individual, including but not
limited to, for example, blood, plasma, serum, spinal fluid, lymph
fluid, the external sections of the skin, respiratory, intestinal,
and genitourinary tracts, tears, saliva, milk, cells (including but
not limited to blood cells), tumors, organs, and also samples of in
vitro cell culture constituents.
[0042] The term "biological sources" as used herein refers to the
sources from which the target polynucleotides are derived. The
source can be any form of "biological sample" as described above,
including but not limited to, cell, tissue or fluid. "Different
biological sources" can refer to different cells, tissues or organs
of the same individual, or cells, tissues or organs from different
individuals of the same species, or cells, tissues or organs from
different species. The term may also refer to cells, especially
human cells, such as those that are malignant or otherwise
associated with cancer, especially breast cancer; and cells that
are laser-captured (laser capture microdissection) from fixed
tissues from model organisms of human diseases or actual human
tissue (postmortem or biopsy material).
[0043] To "inhibit" is to decrease or reduce an activity, function,
and/or amount as compared to a reference.
[0044] A "complex" is an assembly of components. A complex may or
may not be stable and may be directly or indirectly detected. For
example, as is described herein, given certain components of a
reaction, and the type of product(s) of the reaction, existence of
a complex can be inferred. For purposes of this invention, a
complex is generally an intermediate with respect to the final
amplification product(s).
[0045] A "portion" or "region," used interchangeably herein, of a
polynucleotide or oligonucleotide is a contiguous sequence of 2 or
more bases. In other embodiments, a region or portion is at least
about any of 3, 5, 10, 15, 20, 25 contiguous nucleotides.
[0046] A region, portion, or sequence which is "adjacent" to
another sequence directly abuts that region, portion, or sequence.
For example, an RNA portion which is adjacent to a 5' DNA portion
of a composite primer directly abuts that region.
[0047] A "reaction mixture" is an assemblage of components, which,
under suitable conditions, react to form a complex (which may be an
intermediate) and/or a product(s).
[0048] It must be noted that as used in this specification and the
appended claims, the singular forms "a", "an" and "the" include
corresponding plural references unless the context clearly dictates
otherwise.
[0049] "Expression" includes transcription of a deoxyribonucleic
acid and/or translation of a ribonucleic acid.
[0050] As used herein, the term "comprising" and its cognates are
used in their inclusive sense; that is, equivalent to the term
"including" and its corresponding cognates.
[0051] Conditions that "allow" an event to occur or conditions that
are "suitable" for an event to occur, such as hybridization, strand
extension, and the like, or "suitable" conditions are conditions
that do not prevent such events from occurring. Thus, these
conditions permit, enhance, facilitate, and/or are conducive to the
event. Such conditions, known in the art and described herein,
depend upon, for example, the nature of the nucleotide sequence,
temperature, and buffer conditions. These conditions also depend on
what event is desired, such as hybridization, cleavage, strand
extension or transcription.
[0052] Sequence "mutation," as used herein, refers to any sequence
alteration in a sequence of interest in comparison to a reference
sequence. A reference sequence can be a wild type sequence or a
sequence to which one wishes to compare a sequence of interest. A
sequence mutation includes single nucleotide changes, or
alterations of more than one nucleotide in a sequence, due to
mechanisms such as substitution, deletion or insertion. Single
nucleotide polymorphism (SNP) is also a sequence mutation as used
herein.
[0053] The term "3'" (three prime) generally refers to a region or
position in a polynucleotide or oligonucleotide 3' (downstream)
from another region or position in the same polynucleotide or
oligonucleotide.
[0054] The term "5'" (five prime) generally refers to a region or
position in a polynucleotide or oligonucleotide 5' (upstream) from
another region or position in the same polynucleotide or
oligonucleotide.
[0055] The term "3'-DNA portion," "3'-DNA region," "3'-RNA
portion," and "3'-RNA region," refer to the portion or region of a
polynucleotide or oligonucleotide located towards the 3' end of the
polynucleotide or oligonucleotide, and may or may not include the
3' most nucleotide(s) or moieties attached to the 3' most
nucleotide of the same polynucleotide or oligonucleotide. The 3'
most nucleotide(s) can be preferably from about 1 to about 20, more
preferably from about 3 to about 18, even more preferably from
about 5 to about 15 nucleotides.
[0056] The term "5'-DNA portion," "5'-DNA region," "5'-RNA
portion," and "5'-RNA region," refer to the portion or region of a
polynucleotide or oligonucleotide located towards the 5' end of the
polynucleotide or oligonucleotide, and may or may not include the
5' most nucleotide(s) or moieties attached to the 5' most
nucleotide of the same polynucleotide or oligonucleotide. The 5'
most nucleotide(s) can be preferably from about 1 to about 20, more
preferably from about 3 to about 18, even more preferably from
about 5 to about 15 nucleotides.
[0057] "Detection" includes any means of detecting, including
direct and indirect detection. For example, "detectably fewer"
products may be observed directly or indirectly, and the term
indicates any reduction (including no products). Similarly,
"detectably more" product means any increase, whether observed
directly or indirectly.
[0058] Unless defined otherwise all technical and scientific terms
used herein have the same meaning as commonly understood to one of
ordinary skill in the art to which this invention belongs.
B. General Techniques
[0059] The practice of the present invention will employ, unless
otherwise indicated, conventional techniques of molecular biology
(including recombinant techniques), microbiology, cell biology,
biochemistry, and immunology, which are within the skill of the
art. Such techniques are explained fully in the literature, such
as, "Molecular Cloning: A Laboratory Manual", second edition
(Sambrook et al., 1989); "Oligonucleotide Synthesis" (M. J. Gait,
ed., 1984); "Animal Cell Culture" (R. I. Freshney, ed., 1987);
"Methods in Enzymology" (Academic Press, Inc.); "Current Protocols
in Molecular Biology" (F. M. Ausubel et al., eds., 1987, and
periodic updates); "PCR: The Polymerase Chain Reaction", (Mullis et
al., eds., 1994).
[0060] Primers, oligonucleotides and polynucleotides employed in
the present invention can be generated using standard techniques
known in the art.
[0061] While the present invention may be most commonly practiced
in solution, all or part thereof may be practiced as part of a
solid (or immobilized) or in situ state. For example, and without
limiting the invention, synthesis of the first cDNA strand may be
conducted in situ or with a first primer promoter oligonucleotide
that is immobilized on a solid support (such as, but not limited
to, a bead, or a membrane or the surface of a solid container).
C. Promoter-Primer Oligonucleotides
[0062] In some embodiments, the methods employ a promoter sequence
for transcription which is provided by a promoter-primer
oligonucleotide. A promoter-primer for use in the methods and
compositions of the present invention is a single-stranded
polynucleotide, generally DNA, comprising a promoter sequence that
is designed for formation of a double stranded promoter of an RNA
polymerase, and a portion capable of hybridizing to a template
sequence, preferably at or near its 3' end. In one embodiment, the
promoter sequence is located in the 5' portion of the
oligonucleotide and the hybridizing sequence is located in the 3'
portion of the oligonucleotide. In another embodiment, and
typically, the promoter and hybridizing sequences are different
sequences. In another possible embodiment, the promoter and
hybridizing sequences overlap in sequence identity. In yet another
embodiment, the promoter and hybridizing sequences are the same
sequence, and thus are in the same location on the promoter-primer.
In the embodiments wherein hybridization of the promoter-primer to
a template results in a duplex comprising an overhang, DNA
polymerase may be used to fill in the overhang to create a double
stranded promoter capable of effecting transcription by a suitable
RNA polymerase.
[0063] A number of RNA polymerase promoters may be used for the
promoter region of the promoter-primer. Suitable promoter regions
will be capable of initiating transcription from an operationally
linked DNA sequence in the presence of ribonucleotides and an RNA
polymerase under suitable conditions. The promoter region will
usually comprise between about 15 and 250 nucleotides, preferably
between about 17 and 60 nucleotides, from a naturally occurring RNA
polymerase promoter, a consensus promoter region, or an artificial
promoter region, as described in Alberts et al. (1989) in Molecular
Biology of the Cell, 2d ed. (Garland Publishing, Inc.). In general,
prokaryotic promoters are preferred over eukaryotic promoters, and
phage or virus promoters are most preferred. As used herein, the
term "operably linked" refers to a functional linkage between the
affecting sequence (typically a promoter) and the controlled
sequence (the mRNA binding site). The promoter sequence can be from
a prokaryotic or eukaryotic source. Representative promoter regions
of particular interest include T7, T3 and SP6 as described in
Chamberlin and Ryan, The Enzymes (ed. P. Boyer, Academic Press, New
York) (1982) pp 87-108. In a preferred embodiment, the RNA
polymerase promoter sequence is a T7 RNA polymerase promoter
sequence comprising at least nucleotides -17 to +6 of a wild-type
T7 RNA polymerase promoter sequence, preferably joined to at least
20, preferably at least 30 nucleotides of upstream flanking
sequence, particularly upstream T7 RNA polymerase promoter flanking
sequence. Additional downstream flanking sequence, particularly
downstream T7 RNA polymerase promoter flanking sequence, e.g.
nucleotides +7 to +10, may also be advantageously used. For
example, in one particular embodiment, the promoter comprises
nucleotides -50 to +10 of a natural class III T7 RNA polymerase
promoter sequence.
[0064] In some embodiments, the promoter-primer comprises an
intervening anchor sequence between a promoter sequence and a
portion capable of hybridizing to the 3' end of a polynucleotide
template. Suitable length of the intervening anchor sequence can be
empirically determined, and can be at least about 1, 2, 4, 6, 8,
10, 12, 15 nucleotides. Suitable sequence identity of the
intervening anchor sequence can also be empirically determined, and
the sequence is designed to preferably, but not necessarily,
enhance degree of amplification as compared to omission of the
sequence. In one embodiment, the intervening sequence is a sequence
that is designed to provide for enhanced, or more optimal,
transcription by the RNA polymerase used. Generally, the sequence
is not related (i.e., it does not substantially hybridize) to the
target nucleic acid. More optimal transcription occurs when
transcriptional activity of the polymerase from a promoter that is
operatively linked to said sequence is greater than from a promoter
that is not so linked. The sequence requirements within the actual
promoter for optimal transcription are generally known in the art
as previously described for various DNA dependent RNA polymerases,
such as in U.S. Pat. Nos. 5,766,849 and 5,654,142, and can also be
empirically determined.
[0065] The length of the portion of the promoter-primer that
hybridizes to a template is preferably from about 5 to about 50
nucleotides, more preferably from about 10 to about 40 nucleotides,
even more preferably from about 15 to about 35 nucleotides, and
most preferably from about 20 to 30 nucleotides. In some
embodiments, the hybridizing portion is at least about any of the
following: 3, 5, 10, 15, 20; and less than about any of the
following: 30, 40, 50, 60. The complementarity of the hybridizing
portion is preferably at least about 25%, more preferably at least
about 50%, even more preferably at least about 75%, and most
preferably at least about 90% to 100%, to its intended binding
sequence on the target nucleic acid. For the amplification of
polyadenylated target polynucleotides, the primer portion is
preferably poly dT of the lengths described above and below.
[0066] Primer, promoter-primer and anchor oligonucleotides
described above and throughout this specification may be prepared
using any suitable method, such as, for example, the known
phosphotriester and phosphite triester methods, or automated
embodiments thereof. Oligonucleotides of the invention can be
synthesized by a number of approaches, e.g. Ozaki et at, Nucleic
Acids Research, 20:5205-5214 (1992); Agarwal et at, Nucleic Acids
Research, 18:5419-5423 (1990); or the like. The oligonucleotides of
the invention may be conveniently synthesized on an automated DNA
synthesizer, e.g. an Applied Biosystems, Inc. Foster City, Calif.)
model 392 or 394 DNA/RNA Synthesizer, using standard chemistries,
such as phosphoramidite chemistry, e.g. disclosed in the following
references: Beaucage and Iyer, Tetrahedron, 48:2223-2311 (1992);
Molko et al, U.S. Pat. Nos. 4,980,460; Koster et al, U.S. Pat. No.
4,725,677; Caruthers et al, U.S. Pat. Nos. 4,415,732; 4,458,066;
and 4,973,679; and the like. Alternative chemistries, e.g.
resulting in non-natural backbone groups, such as phosphorothioate,
phosphoramidate, and the like, may also be employed provided that
the hybridization efficiencies of the resulting oligonucleotides
and/or cleavage efficiency of the exonuclease employed are not
adversely affected. Preferably, the oligonucleotide is in the range
of 20-100 nucleotides in length. More preferably, the
oligonucleotide is in the range of 20-85 nucleotides in length. The
precise sequence and length of an oligonucleotide of the invention
depends in part on the nature of the target polynucleotide to which
it binds. The binding location and length may be varied to achieve
appropriate annealing and melting properties for a particular
embodiment. Guidance for making design choices can be found in many
of the above-cited references describing the "Taqman" type of
assays. One method for synthesizing oligonucleotides on a modified
solid support is described in U.S. Pat. No. 4,458,066. It is also
possible to use a primer that has been isolated from a biological
source (such as a restriction endonuclease digest of cloned genomic
DNA).
[0067] In preferred embodiments of the invention, the molar ratio
of primers to template sequences is from about 500:1 to about
8000:1. More preferred are molar ratios of about 1000:1, about
1500:1, about 1600:1, about 1700:1, about 1800:1, about 1900:1,
about 2000:1, about 2500:1, about 3000:1, about 3500:1, about
4000:1, about 4500:1, about 5000:1, about 5500:1, about 6000:1,
about 6500:1, about 7000:1, and about 7500:1. Most preferred are
molar ratios of about 1100:1, about 1200:1, about 1300:1, and about
1400:1. Lower ratios of primer to template are preferred to reduce
undesirable effects of excess primers in subsequent reactions.
Molar ratio of primer to RNA template may be determined as follows:
assuming 2% mRNA content in total RNA and an average mRNA size of
2000 bases, each base at 300 g/mol, 5 ng of primer with 5 ng of
total RNA is approximately a molar ratio (primer:mRNA) of about
1300:1.
D. DNA Polymerase, Ribonuclease and RNA Polymerase
[0068] The amplification methods of the invention employs the
following enzymatic activities: DNA polymerase, optionally
ribonuclease such as RNase H, and a DNA dependent RNA polymerase.
Preferred embodiments of the invention include the use of an RNase
H activity, whether present as part of a DNA polymerase activity or
as exogenously supplied. Optionally, the methods of the invention
include the use of an exonuclease activity (such as but not limited
to exonuclease I from E. coli, SI nuclease, mung bean exonuclease,
or one or more than one single stranded DNA exonuclease in general)
to degrade excess primers (not used to prime first strand cDNA
synthesis) as needed. Preferred embodiments of the invention
include the use of exonuclease I which may be readily inactivated
before proceeding on to subsequent reactions. Other preferred
embodiments couple the use of exonuclease to degrade excess first
primer with the use of an exonuclease deficient polymerase to
synthesize the second cDNA strand while protecting the primers used
for second strand synthesis.
[0069] DNA polymerases for use in the methods and compositions of
the present invention are capable of effecting extension of the
composite primer according to the methods of the present invention.
Accordingly, a preferred polymerase is one that is capable of
extending a nucleic acid primer along a nucleic acid template that
is comprised at least predominantly of deoxyribonucleotides. The
polymerase should be able to displace a nucleic acid strand from
the polynucleotide to which the displaced strand is bound, and,
generally, the more strand displacement capability the polymerase
exhibits (i.e., compared to other polymerases which do not have as
much strand displacement capability) is preferable. Preferably, the
DNA polymerase has high affinity for binding at the 3'-end of an
oligonucleotide hybridized to a nucleic acid strand. Preferably,
the DNA polymerase does not possess substantial nicking activity.
Preferably, the polymerase has little or no 5'->3' exonuclease
activity so as to minimize degradation of primer, termination or
primer extension polynucleotides. Generally, this exonuclease
activity is dependent on factors such as pH, salt concentration,
whether the template is double stranded or single stranded, and so
forth, all of which are familiar to one skilled in the art. Mutant
DNA polymerases in which the 5'->3' exonuclease activity has
been deleted, or in which both 5'>3' and 3'->5 exonuclease
activity has been deleted are known in the art and are suitable for
the amplification methods described herein. Suitable DNA
polymerases for use in the methods and compositions of the present
invention may include those disclosed in U.S. Pat. Nos. 5,648,211
and 5,744,312, which include exo.sup.- Vent (New England Biolabs),
exo Deep Vent (New England Biolabs), Bst (BioRad), exo.sup.- Pfu
(Stratagene), Bca (Panvera), sequencing grade Taq (Promega), and
thermostable DNA polymerases from Thermoanaerobacter
thermohydrosulfuricus. It is preferred that the DNA polymerase
displaces primer extension products from the template nucleic acid
in at least about 25%, more preferably at least about 50%, even
more preferably at least about 75%, and most preferably at least
about 90%, of the incidence of contact between the polymerase and
the 5' end of the primer extension product. In some embodiments,
the use of thermostable DNA polymerases with strand displacement
activity is preferred. Such polymerases are known in the art, such
as those described in U.S. Pat. No. 5,744,312 (and references cited
therein). Preferably, the DNA polymerase has little to no
proofreading activity.
[0070] While the invention simply requires the use of DNA
polymerase activity, the invention is preferably practiced with a
combination of polymerase activities wherein the individual
polymerases are individually selected from exonuclease deficient
Klenow, Taq polymerase, and Sequenase.TM., optionally in the
presence of RNase H, in the synthesis of the second strand of the
cDNA molecule corresponding to the target polynucleotide. Most
preferred is the use of exonuclease deficient Klenow alone or in
combination with Taq polymerase in the presence or absence of RNase
H. The combination of exonuclease deficient Klenow and Taq
polymerase resulted in the unexpected discovery that this
combination resulted in improved cDNA synthesis and hence aRNA
production over other polymerases. Methods to test and optimize
various polymerase activities and conditions, including the
identification of activities and conditions which are not suitable
for research or commercial applications, for use in the practice of
the present invention are known in the art.
[0071] Preferred conditions for the use of the exonuclease
deficient Klenow and Taq polymerase combination is to permit the
Klenow to function at 37.degree. C. followed by an increase in
temperature to permit Taq polymerase to function under reduced
Klenow activity conditions. In a preferred embodiment of the
invention, the two enzymes are added to a mixture of first strand
cDNA and random primers when they have been removed (such as, but
not limited to, placement in ice or an ice water bath) from heat
treatment at about 95.degree. C. The mixture may then be placed at
room temperature for about 5 to about 10 minutes followed by an
increase to 37.degree. C. for about 10 to about 30 minutes followed
by about 72.degree. C. for about 5 to about 15 minutes. In
preferred embodiments of the invention, the mixture is maintained
at or above room temperature after addition of random primers and
DNA polymerase activity and until completion of synthesis of the
second cDNA strand.
[0072] In alternate embodiments of the invention, the times and
temperatures may be adjusted relative to the above conditions, but
the time period for second strand cDNA synthesis will preferrably
not exceed about 3 hours andis preferrably completed in the range
of about 1 to about 2 hours. Most preferred is the time period to
be less than about one hour or about 30 minutes.
[0073] Any reverse transcriptase may be used in the practice of the
invention, including, but not limited to, Superscript RTII
(optionally RNase H minus), "regular" MMLV-RT (with intrinsic
RNaseH activity), AMV RT, or combinations thereof.
[0074] The ribonuclease for use in the methods and compositions of
the present invention is capable of cleaving ribonucleotides in an
RNA/DNA hybrid. Preferably, the ribonuclease cleaves
ribonucleotides regardless of the identity and type of nucleotides
adjacent to the ribonucleotide to be cleaved. It is preferred that
the ribonuclease cleaves independent of sequence identity. Examples
of suitable ribonucleases for the methods and compositions of the
present invention are well known in the art, including ribonuclease
H(RNase H) from E. coli or RNaseH associated with retroviral
reverse transcriptases.
E. Amplification of Polynucleotides and Anchoring of Amplification
Products
[0075] The present invention features methods for generating
amplification products corresponding to a target polynucleotide
wherein the amplification products optionally have one or more
anchored known sequences. The starting polynucleotide is a single
stranded DNA or RNA which is amplified by the methods of this
invention.
[0076] In one aspect of the invention, a method for the preparation
of a double stranded cDNA from a target RNA polynucleotide is
provided. For example, and when a mRNA is the target
polynucleotide, the first strand of the cDNA is prepared by the use
of a primer, optionally containing an anchor sequence and/or a
promoter region, complementary to sequences at or near the 3' end
of the mRNA. The primer and target polynucleotide are annealed to
form a complex which is then contacted with reverse transcriptase
(RT) activity. After primer extension by the RT activity, the
mRNA/DNA hybrid duplex may be denatured (by heating or treating
with base such as NaOH) to separate the two strands or treated with
an RNase H activity (or base such as NaOH) to nick or degrade the
mRNA.
[0077] Where the mRNA is removed or degraded, the first strand cDNA
is contacted with random primers, optionally containing an anchor
sequence and/or a promoter region, and allowed to anneal to form
complexes which contain random primers hybridized to the first
strand cDNA at a plurality of positions. These complexes are then
contacted with a DNA dependent DNA polymerase activity to extend
the primers and produce the second cDNA strand to form double
stranded cDNA. The use of random primers results in a plurality of
cDNAs contain all or part of the sequence found in the original
target mRNA polynucleotide in individual cDNAs.
[0078] As described herein, a variety of DNA polymerase activities
may be used, especially activities that are proficient at
initiating primer extension reactions and processive in the
polymerase activity. A preferred polymerase activity for the
practice of the invention is a combination of exonuclease deficient
Klenow and Taq polymerase activities as described herein.
[0079] It is helpful to note that the method of the invention is
distinct from other protocols where the first strand cDNA is
contacted with a primer containing a known sequence for annealing
to the first strand cDNA. The method is also distinct from coupled
reverse transcription/PCR reactions wherein the second strand of
the cDNA is synthesized only with a DNA polymerase more active at
temperatures above 50.degree. C. than at room temperature
("thermostable polymerase"). The synthesis of the second strand of
the cDNA in coupled PCR approach may be viewed as the "first round"
of the PCR reaction. The method also differs from PCR in that there
is no repetitive thermal cycling of the reaction mixture or the
complex between primer and cDNA strand.
[0080] FIG. 1 illustrates an amplification method according to this
invention where the template is an eukaryotic mRNA although the use
of single or double stranded DNA or non-messenger RNA as template
are also encompassed by the method. The method shown in FIG. 1
comprises both "round one" and two possibilities for "round two".
"Round one" includes first contacting a (+) strand of a mRNA target
with an oligonucleotide comprising poly dT, A1, and T7 promoter
sequences. The presence of the A1 anchor sequence is optional and
it is not require for the practice of the invention. Since most
eukaryotic mRNA molecules are polyadenylated at their 3' end, the
oligonucleotide preferably comprises an oligo-dT primer sequence of
at least about 8 nucleotides in length and preferably between about
10 and 30 nucleotides in length. A T7 RNA polymerase promoter
region is coupled indirectly to the 5' end of the poly-dT primer.
Under conditions of the reaction, and as shown in FIG. 1, the
poly-dT portion hybridizes to the poly-A stretch at the 3' end of
the mRNA target, whereas the promoter sequence does not readily
hybridize to the target mRNA.
[0081] Where the starting template is not an eukaryotic mRNA (i.e.,
it does not have a polyA stretch at the 3' end) the first primer
sequence may comprise of a degenerate (random) sequence or a
specific sequence known to be present at or near the 3' end of the
template.
[0082] Following extension of the oligonucleotide primer, a (-)
first strand cDNA is obtained having a sequence complementary to
the mRNA. This cDNA strand comprises an poly dT region and a
promoter sequence strand.
[0083] The cDNA strand is then separated from the mRNA template by
denaturing conditions. These include, but are not limited to,
treating the RNA:cDNA duplex with alkali, preferably 0.5 N NaOH, or
heating to a temperature (e.g., 95.degree. C.) for a length of time
(e.g., 5 minutes) that yields sufficient denaturation. These
conditions may also be used to eliminate reverse transcriptase
activity prior to further manipulations.
[0084] A second oligonucleotide sufficiently complementary to the
cDNA strand is then hybridized to the cDNA strand. The second
oligonucleotide is exogenously provided and comprises either a
random primer or a sequence complementary to a known sequence
present in the cDNA strand. A double-stranded DNA is prepared by
extending the second oligonucleotide to form a second DNA strand
complementary to the cDNA strand in the presence of a DNA-dependent
DNA polymerase and appropriate deoxyribonucleotides (dNTPs). A
functional double-stranded promoter is thereby formed at an end of
the double-stranded DNA operably connected to and upstream of the
polynucleotide sequence to be amplified. As shown in FIG. 1, the
promoter is operably linked to an end corresponding to the 3' end
of the original mRNA template. The promoter may comprise a T3, T7,
SP6 or any other suitable RNA polymerase promoter known in the art.
For example, and as shown in FIG. 1, a T7 promoter is formed in the
process.
[0085] The T7 promoter is contacted with the corresponding T7 RNA
polymerase enzyme capable of initiating transcription from the
promoter, and one or more copies of an amplified RNA (aRNA) is
transcribed as the amplification products. The amplified RNAs
(aRNAs) comprise in a 5' to 3' order, an poly-U section generated
from the poly-dA:dT portion of the double stranded DNA, and a (-)
strand sequence complementary to all or part of the mRNA template.
Furthermore, most aRNAs can be approximately the same lengths if
defined by the hybridization sites of the first and second
oligonucleotide primers.
[0086] The above may be summarized as a method of amplifying RNA
sequences complementary to one or more than one target
polynucleotide that is single stranded or made single stranded,
comprising a) forming double stranded cDNA templates containing
sequences present in said target polynucleotide, wherein said
sequences are operably linked to a promoter region, by i) annealing
said single stranded target polynucleotide with a first
oligonucleotide comprising a primer region operably linked to a
promoter region, to form a first complex, ii) synthesizing a first
strand cDNA by reverse transcription of said first complex, iii)
annealing said first stranded cDNA, after denaturing the mRNA/cDNA
hybrid or degrading the RNA from said hybrid, with a plurality of
second oligonucleotides comprising a random primer region to form a
population of second complexes, and iv) forming double stranded
cDNA templates from said population of second complexes with DNA
dependent DNA polymerase activity; and b) transcribing said cDNA
templates with an RNA polymerase capable of initiating
transcription via said promoter region to produce RNA containing
sequences complementary to said target polynucleotide. This may be
practiced where the target polynucleotide is an mRNA molecule or a
plurality of mRNA isolated from a biological source, such as a
cell. When mRNA is the target polynucleotide, the first primer
region preferably contains a poly dT sequence of about 8 or more
nucleotides and the random primer region used to synthesize the
second cDNA strand are preferably about six to about nine
nucleotides in length. Random primers of more than six, such as
seven, eight, nine, ten, eleven, or twelve nucleotides, are
preferably used. Preferably, the second cDNA strand is synthesized
by use of exonuclease deficient Klenow and Taq polymerase
activities.
[0087] Of course in any embodiment of the invention any of the
nucleic acids (DNA or RNA) may be labeled during the synthesis of
the polynucleotide chain.
[0088] In an optional embodiment of the invention, the synthesis of
the first and/or second cDNA strand is conducted in the presence of
a repetitive polynucleotide such as, but not limited to, polymers
of deoxyribo- or ribo-nucleotides of adenosine, cytosine,
thymidine, guanine, or inosine. Particularly preferred is the use
of poly adenosine (poly A), poly dA, and poly inosine (poly I). The
inclusion of such polymers may be especially advantageous in
situations where the amount of the target polynucleotide,
especially target mRNA, is very low, such as in the picogram range.
When higher amounts of target are higher, such as in the nanogram
range, there is less added benefit to the inclusion of such
polymers.
[0089] In "round two" of FIG. 1, the aRNA of "round one" is used as
the template to prepare additional double stranded DNAs to amplify
more aRNA. This is exemplified by the use of a primer to generate a
first strand DNA which is complementary to all or part of the aRNA
template, followed by generation of the second strand DNA by use of
the T7 promoter containing oligonucleotide from "round one". The
resultant double stranded DNA may be used to transcribe aRNAs
containing all or part of the sequences of the aRNA template. The
transcribed aRNAs would contain all of the sequences of the aRNA
template if the primer used to generate the first strand DNA was
complementary to the 3' end of the aRNA template. The transcribed
aRNAs would contain part of the sequences of the aRNA template if
the primer used to generate the first strand DNA was complementary
to an internal portion of the aRNA template.
[0090] The above may be summarized as increasing the amplification
of RNA sequences complementary to a target polynucleotide by
preparing additional double stranded DNA templates, comprising all
or part of the sequence of the aRNA, and initiating transcription
from the additional templates, by annealing said aRNA to a third
oligonucleotide comprising a primer region to form a third complex,
synthesizing the first strand of said additional double stranded
DNA templates by reverse transcription of said third complex,
annealing said first strand of additional DNA templates, after
denaturing the aRNA/DNA hybrids or degrading the aRNA from said
hybrids, with said first oligonucleotide comprising an operably
linked promoter region to form a fourth complex, forming additional
double stranded DNA templates from said fourth complex with DNA
dependent DNA polymerase activity, and transcribing said double
stranded DNA templates with an RNA polymerase capable of initiating
transcription via said promoter region to produce additional
amplified RNA (aRNA) containing sequences complementary to said
target polynucleotide. The random primer region of the third
oligonucleotide is preferably about six to about nine nucleotides
in length and a combination of exonuclease deficient Klenow and Taq
polymerase activities is preferably used to synthesize the double
stranded DNA templates from the fourth complex. Alternatively, the
third oligonucleotide may comprise a known primer sequence,
optionally complementary to the 3' end of aRNA. In "round two
modified" as shown in FIG. 1, the aRNA of "round one" is used to
prepare additional double stranded DNAs containing promoters at
both ends. This is exemplified by the use of a T3 promoter
containing primer to generate a first strand DNA which is
complementary to all or part of the aRNA template, followed by
generation of the second strand DNA by use of the T7 promoter
containing oligonucleotide from "round one". Optionally, this
oligonucleotide may be modified to exclude the promoter introduced
in "round one" so that the method may be adapted to exclude
replication of the promoter region introduced in "round one". The
resultant double stranded DNA may be used to transcribe aRNAs
containing all or part of the sequences of the aRNA template (by
using a T7 RNA polymerase) or to transcribe a sequence
complementary to all or part of the aRNA template (by using a T3
RNA polymerase). The transcribed aRNAs would contain all of the
sequences of the aRNA template if the primer used to generate the
first strand DNA was complementary to the 3' end of the aRNA
template. The transcribed aRNAs would contain part of the sequences
of the aRNA template if the primer used to generate the first
strand DNA was complementary to an internal portion of the aRNA
template.
[0091] The above may be summarized as a method of amplifying RNA
sequences present in one or more than one target polynucleotide
that is single stranded or made single stranded by modifying "round
two" by i) annealing said aRNA with a third oligonucleotide
comprising a primer region operably linked to a promoter region to
form a third complex, ii) synthesizing the first strand of said
additional DNA template by reverse transcription of said third
complex, iii) annealing said first strand of additional DNA
template, after denaturing the aRNA/DNA hybrid or degrading the
aRNA from said hybrid, with said first oligonucleotide to form a
population of fourth complexes, and iv) forming additional double
stranded DNA templates from said population of fourth complexes
with DNA dependent DNA polymerase activity; and then transcribing
said additional DNA templates with an RNA polymerase capable of
initiating transcription via the promoter region of said first
oligonucleotide to produce amplified RNA (aRNA) containing
sequences complementary to said target polynucleotide or via the
promoter region of said third oligonucleotide to produce aRNA
containing sequences present in said target polynucleotide. The
third oligonucleotide may again comprise a random primer region,
preferably from at least about six random nucleotides to at least
about nine random nucleotides, or a known primer sequence,
optionally complementary to the 3' end of said aRNA. The promoter
region of the third oligonucleotide preferably comprises a T3
promoter region.
[0092] In all of the above, the promoter region of the first
oligonucleotide preferably comprises a T7 promoter region.
F. Additional Rounds of Amplification
[0093] Where the total levels of starting RNA target polynucleotide
is limiting (e.g., <20 ng of total RNA or <.about.400 pg of
mRNA in the form of poly (A) RNA), the second and further rounds of
amplification of the aRNA may be performed according to methods of
the present invention. Such additional rounds may of course be
performed more than once, such as, but not limited to, twice, three
times, or four times.
[0094] The amplification, which will typically be at least about
20-40, typically to 50 to 100 or 250-fold, or 500 to 1000-fold, or
500-2000 fold or more per round of amplification, can be achieved
from nanogram quantities or less of total RNA (and thus picograms
of starting material of poly(A) RNA), and is economical and simple
to perform under standard molecular biology laboratory conditions.
It is also easily adaptable into kit form.
[0095] In an optional embodiment of the invention, the synthesis of
one or both cDNA strands is conducted in the presence of a
repetitive polynucleotide such as, but not limited to, polymers of
deoxyribo- or ribo-nucleotides of adenosine, cytosine, thymidine,
guanine, or inosine. Particularly preferred is the use of poly
adenosine (poly A), poly dA, and poly inosine (poly I). The
inclusion of such polymers may be especially advantageous in
situations where the amount of the target polynucleotide,
especially target mRNA, is very low, such as in the picogram range.
When higher amounts of target are higher, such as in the nanogram
range, there is less added benefit to the inclusion of such
polymers.
[0096] Use of poly T in the purification of total RNA has been
evaluated by Winslow et al. (Nucl. Acids Res. 19(12):3251-3253
1991).
G. Uses: Detection of Polynucleotide Expression and Related
Diagnostic Methods
[0097] In specific non-limiting embodiments, the present invention
provides methods useful for detecting cancer cells, facilitating
diagnosis of cancer and the severity of a cancer (e.g., tumor
grade, tumor burden, and the like) in a subject, facilitating a
determination of the prognosis of a subject, and assessing the
responsiveness of the subject to therapy (e.g., by providing a
measure of therapeutic effect through, for example, assessing tumor
burden during or following a chemotherapeutic regimen). Detection
can be based on detection of a polynucleotide that is
differentially expressed in a cell, and/or detection of a
polypeptide encoded by a polynucleotide that is differentially
expressed in a cell. The detection methods of the invention can be
conducted in vitro or in vivo, on isolated cells, or in whole
tissues or a bodily fluid (e.g., blood, plasma, serum, urine, and
the like).
[0098] The aRNA of mRNAs from live or fixed (from tissue sections
via laser capture microdissection or other means of dissection),
single or multiple cells can be amplified sufficiently to generate
the following: labeled probes for hybridization experiments (e.g.,
DNA microarrays or macroarrays) thus generating gene expression
profiles of various cell types or individual cells (in a manner
analogous to that disclosed by Serafini et al., U.S. Pat. No.
6,110,711); cDNA libraries that contain mRNAs from selected cells
and subsequently used to generate normalized libraries or various
subtractive hybridization methodologies; cDNA that then is used for
RT-PCR or quantitative RT-PCR (to subsequently quantitate
individual mRNAs); cDNA for subsequent use for various methods that
yield differentially expressed genes (i.e., differential display
and representational difference analysis (RDA)); and amplified RNA
that can be used in various subtraction methodologies, such as
subtractive hybridization. The amplification of mRNAs from a single
cell is a preferred embodiment of the invention and offers
advantages in eliminating the possibility of amplifying
heterologous mRNA due to the use of two or more cells.
[0099] As noted above, the methods of the present invention may be
used to detect expression of a particular gene sequence (including,
but not limited to, sequences that differ due to genetic
polymorphism) on a cell or population of cells by determining the
presence or absence of RNA transcribed from the particular gene
sequence in the amplified RNA population. The level of expression
of the particular gene may also be determined relative to other
RNAs amplified within the overall population of amplified RNAs. The
level of expression between different tissues or cell types (or
different physiological states of the same tissue or cell type) may
also be compared by preparing amplified RNAs from the different
tissues or cell types (or the same tissue or cell type under
different physiological states, such as, but not limited to, cancer
and non-cancer cells) and comparing the species of amplified RNAs
produced from the different sources. Different physiological states
of the invention include, but are not limited to, different drug
(or other active agent) induced states, different behavioral
states, different developmental states, different states of
stimulation, different states of activation or inhibition, or
different states of arousal.
[0100] The present methods may also be used to produce amplified
RNAs that are used as subtractive hybridization probes or used as
the templates for members of a cDNA library (after a second round
of amplification and without in vitro transcription, for example).
The techniques for subtractive hybridization are known in the art,
and the use of the present methods provide an advantageous means of
producing RNAs for use in subtraction. Similarly, the techniques
for preparing a cDNA library are known in the art and the present
methods provide an advantageous means of producing the member
sequences of a library.
H. Labeling and Detection of Amplified Molecules
[0101] Detecting labeled target polynucleotides can be conducted by
standard methods used to detect the labeled sequences. For example,
fluorescent labels or radiolabels can be detected directly such as
incorporating fluorescent nucleotide dyes into cDNA generation
using amplified RNA as template. Other labeling techniques may
require that a label such as biotin or digoxigenin be incorporated
into the DNA or RNA (during amplification or within cDNA generated
from amplified RNA) and detected by an antibody or other binding
molecule (e.g. streptavidin) that is either labeled or which can
bind a labeled molecule itself. For example, a labeled molecule can
be an anti-streptavidin antibody or anti-digoxigenin antibody
conjugated to either a fluorescent molecule (e.g. fluorescein
isothiocyanate, Texas red and rhodamine), or an enzymatically
active molecule. Whatever the label on the newly synthesized
molecules, and whether the label is directly in the DNA or
conjugated to a molecule that binds the DNA (or binds a molecule
that binds the DNA), the labels (e.g. fluorescent, enzymatic,
chemiluminescent, or colorimetric) can be detected by a laser
scanner or a CCD camera, or X-ray film, depending on the label, or
other appropriate means for detecting a particular label.
[0102] The amplified target polynucleotide can be detected by using
labeled nucleotides (e.g. dNTP-fluorescent label for direct
labeling; and dNTP-biotin or dNTP-digoxigenin for indirect
labeling) incorporated during amplification or by incorporating it
during cDNA synthesis when using amplified RNA as template. For
indirectly labeled DNA, the detection is carried out by
fluorescence or other enzyme conjugated streptavidin or
anti-digoxigenin antibodies. The method employs detection of the
polynucleotides by detecting incorporated label in the newly
synthesized complements to the polynucleotide targets. For this
purpose, any label that can be incorporated into DNA as it is
synthesized can be used, e.g. fluoro-dNTP, biotin-dNTP, or
digoxigenin-dNTP; as described above and are known in the art. In a
differential expression system, amplification products derived from
different biological sources can be detected by differentially
(e.g., red dye and green dye) labeling the amplified target
polynucleotides based on their origins.
[0103] In a preferred embodiment, amplified RNA is used as template
for incorporating fluorescent nucleotides during the subsequent
probe generation via cDNA synthesis.
[0104] For detection, light detectable means are preferred,
although other methods of detection may be employed, such as
radioactivity, atomic spectrum, and the like. For light detectable
means, one may use fluorescence, phosphorescence, absorption,
chemiluminescence, or the like. The most convenient will be
fluorescence, which may take many forms. One may use individual
fluorescers or pairs of fluorescers, particularly where one wishes
to have a plurality of emission wavelengths with large Stokes
shifts (at least 20 nm). Illustrative fluorescers include
fluorescein, rhodamine, Texas red, cyanine dyes, phycoerythrins,
thiazole orange and blue, etc.
[0105] Depending on the particular intended use of the aRNA, the
aRNA may be labeled. One way of labeling which may find use in the
subject invention is isotopic labeling, in which one or more of the
nucleotides is labeled with a radioactive label, such as .sup.32S,
.sup.32P, .sup.3H, or the like. Another means of labeling is
fluorescent labeling in which a fluorescently tagged nucleotide,
e.g. CTP, is incorporated into the aRNA product during
transcription. Fluorescent moieties which may be used to tag
nucleotides for producing labeled antisense RNA include:
fluorescein, the cyanine dyes, such as Cy3, Cy5, Alexa 542, Bodipy
630/650, and the like.
I. Characterization of Nucleic Acids
[0106] The amplification products obtained by the methods of the
invention are particularly amenable to further characterization, in
part because the products are single stranded. The amplified
products, either DNA or RNA, can analyzed using probe hybridization
techniques known in the art, such as Southern and Northern blotting
on a solid support such as, but not limited to, nitrocellulose. The
amplified products can also be analyzed by contacting them with
microarrays comprising oligonucleotide probes or cDNAs. The
identity of the probes provides characterization of the sequence
identity of the amplified products, and thus by extrapolation the
identity of the template nucleic acid present in a sample suspected
of containing said template nucleic acid. The above hybridization
based techniques may also be used to detect expression from a
single gene sequence.
J. Kits
[0107] Also provided are kits for use in the subject invention,
where such kits may comprise containers, each with one or more of
the various reagents (typically in concentrated form) utilized in
the methods, including, for example, buffers, the appropriate
nucleotide triphosphates (e.g. dATP, dCTP, dGTP, dTTP, dUTP, ATP,
CTP, GTP and UTP), reverse transcriptase, DNA polymerase, RNA
polymerase, and one or more sequence-specific primers, degenerate
primers, random primers, poly-dT primers and corresponding
promoter-primers and tagged-primers of the present invention. A
label or indicator describing, or a set of instructions for use of,
kit components in an mRNA amplification method of the present
invention, will also be typically included, where the instructions
may be associated with a package insert and/or the packaging of the
kit or the components thereof.
EXAMPLES
[0108] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how to make and use the present invention, and are
not intended to limit the scope of what the inventors regard as
their invention nor are they intended to represent that the
experiments below are all and only experiments performed. Efforts
have been made to ensure accuracy with respect to numbers used
(e.g. amounts, temperature, etc.) but some experimental errors and
deviations should be accounted for. Unless indicated otherwise,
parts are parts by weight, molecular weight is weight average
molecular weight, temperature is in degrees Celsius, and pressure
is at or near atmospheric.
Example 1
Transcription from T7 RNA Polymerase Promoter
[0109] In one general embodiment of the present invention, cDNA
strands are synthesized from a collection of mRNAs using an
oligonucleotide primer complex. If the target mRNA is the entire
mRNA population, then the primer can be a polythymidylate region
(e.g., about 5 to 25, preferably about 18-21 T residues), which
will bind with the poly(A) tail present on the 3' terminus of each
mRNA. Alternatively, if only a preselected mRNA is to be amplified,
then the primer will be substantially complementary to a section of
the chosen mRNA, typically at the 3' terminus. The promoter region
is located upstream of the primer at its 5' terminus in an
orientation permitting transcription with respect to the mRNA
population utilized. When the second cDNA strand is synthesized,
the promoter sequence will be in correct orientation in that strand
to initiate RNA synthesis using that second cDNA strand as a
template. Preferably, the promoter region is derived from a
prokaryote, and more preferably from the group consisting of SP6,
T3 and T7 phages (Chamberlin and Ryan, in The Enzymes, ed. P. Boyer
(Academic Press, New York) pp. 87-108 (1982), which is incorporated
herein by reference). A preferred promoter region is one that
contains an arbitrary sequence (here for example, part of the M13
forward priming site) 5' to the consensus T7 promoter sequence."
(5' AAA CGA CGG CCA GTG AAT TGT AAT ACG ACT CAC TAT AGG GAG A
3').
[0110] Once the oligonucleotide primer hybridizes to the mRNA, a
first DNA strand is synthesized. This first strand of cDNA is
preferably produced through the process of reverse transcription,
wherein DNA is made from RNA, utilizing reverse transcriptase
following standard techniques. This enzyme, (e.g., MMLV reverse
transcriptase or AMV reverse transcriptase), adds
deoxyribonucleotides to the 3' terminus of the primer (Varmus,
Science 240: 1427-1435 (1988)).
[0111] To complete second strand synthesis, random nonamers
(9-mers) are added to the RNA/cDNA heteroduplex that has been
previously denatured, and with the use of a DNA polymerase
(preferably Klenow plus Taq or exo-Klenow plus Taq) and dNTPs, the
second strand is synthesized. The second strand is generated as
deoxyribonucleotides are added to the 3' terminus of the growing
strand. As the growing strand reaches the 5' terminus of the first
strand DNA, the complementary promoter region of the first strand
will be copied into the double stranded promoter sequence in the
desired orientation.
[0112] Once double stranded cDNA is synthesized then T7 RNA
polymerase is used to generate a plurality of aRNAs via
transcription from the cDNA template. Preferred transcription
conditions employ a class III T7 promoter sequence and a T7 RNA
polymerase under the following reaction conditions: 40 mM Tris pH
7.9, 6 or 10 mM MgCl.sub.2, 2 mM Spermidine, 10 mM DTT, 2 mM NTP
(Pharmacia), 40 units RNAsin (Promega), 300-1000 units T7 RNA
Polymerase (Promega). The enzyme is stored in 20 mM HEPES pH 7.5,
100 mM NaCl, 1 mM EDTA, 1 mM DT'T and 50% Glycerol at a protein
concentration of 2.5 mg/ml and an activity of 300-350 units/.mu.l.
In exemplary demonstrations, 1-3 .mu.L of this polymerase was used
in 50 .mu.L reactions (commercially available transcription kits
may be used in this step). Starting concentrations of template can
vary from sub-picogram quantities (single cell level) to 1 .mu.g or
more of linear DNA.
[0113] The DNA is transcribed into anti-sense RNA (aRNA) by
introducing an RNA polymerase capable of binding to the promoter
region. Amplification occurs because the polymerase repeatedly
recycles on the template (i.e., reinitiates transcription from the
promoter region). This particular technique enables replicating a
broad range of cDNAs without prior cloning into vectors. Recycling
of the polymerase on the same template avoids propagation of
errors.
Example 2
Source of Cell Samples and Isolation of Expressed
Polynucleotides
[0114] Normalized cDNA library is prepared from one patient tumor
tissue and cloned polynucleotides for spotting on microarrays are
isolated from the library. Normal and tumor tissues from other
patients are processed to generate amplified aRNA, which are, in
turn, assessed for expression in microarrays. The objective of
normalization is to generate a cDNA library in which all
transcripts expressed in a particular cell type or tissue are
equally represented (Weissman S M Mol. Biol. Med. 4(3), 133-143
(1987); Patanjali, et al. Proc. Natl. Acad. Sci. USA 88 (1991)),
and therefore isolation of as few as 30,000 recombinant clones in
an optimally normalized library may represent the entire gene
expression repertoire of a cell, estimated to number 10,000 per
cell.
[0115] Cells (.about.100-500 cells) are harvested directly from
frozen sections of tissue by laser capture microdissection (LCM,
Arcturus Engineering Inc., Mountain View, Calif.), carried out
according to methods well known in the art (see, Simone et al. Am
J. Pathol. 156(2):445-52 (2000)), to provide substantially
homogenous cell samples. Total RNA is extracted from LCM-harvested
cells using any known protocol (such as, but not limited to,
commercially available kits including Picopure.TM. from Arcturus
Engineering Inc., Mountain View, Calif.). About 2-10 ng of total
RNA (approximate yield from 100-500 cells) is reverse transcribed
into cDNA and subsequently amplified via two rounds as detailed in
this invention (see example 1) using the modified second round. In
this case (i.e., using the modified second round), the resultant
aRNA generated via T7 RNA polymerase after two rounds of
amplification has the following sequence 5' to 3': anchor 1
sequence, U.sub.21, polynucleotide sequence of a given mRNA,
followed by T3 promoter sequence. The resultant aRNA from two
rounds of amplification is converted into double stranded cDNA
using a primer for first strand synthesis that contains the T3
sequence. Second strand synthesis is initiated via a primer
containing, from 5' to 3', the T7 promoter sequence, anchor 1
followed by 21 dT's. The subsequent cDNA products are size-selected
by agarose gel electrophoresis using standard procedures to remove
small sized cDNA (<100 bp) (Sambrook, J. T., et al. Molecular
Cloning: A Laboratory Manual, 2d ed., Cold Spring Harbor Laboratory
Press, NY). The cDNA is extracted by any known method including,
but not limited to commercially available kits, followed by
normalization of the cDNA using kinetics of hybridization
principles: 1.0 .mu.g of cDNA is denatured by heat at 100.degree.
C. for 10 minutes, and then incubated at 42.degree. C. for at least
12 hours in the presence of 120 mM NaCl, 10 mM Tris.HCl (pH=8.0), 5
mM EDTA.Na+ and 50% formamide. Single-stranded cDNA ("normalized"
cDNA) was purified by hydroxyapatite chromatography (#130-0520,
BioRad, Hercules, Calif.) following the manufacturer's recommended
procedures, amplified into double stranded cDNA via PCR using two
oligonucleotide primers containing T3 and T7 promoter sequences
respectively, and subsequently cloned into plasmid vectors using
standard procedures (Sambrook, J. T., et al. Molecular Cloning: A
Laboratory Manual, 2d ed., Cold Spring Harbor Laboratory Press,
NY). Supercompetent cells (XL-2 Blue Ultracompetent Cells,
Stratagene, California) are transfected with the normalized cDNA
libraries, plated on solid media and grown overnight at 37.degree.
C.
Example 3
Differential Expression Assay
[0116] cDNA probes are prepared from RNA amplified via the present
invention from total RNA that has been extracted from normal and
cancerous cells that are contained within a biopsy/surgical
resection procured via laser capture microdissection (LCM, Arcturus
Engineering Inc., Mountain View, Calif.). Fluorescently labeled
cDNAs prepared from the tumor sample are compared to fluorescently
labeled cDNAs prepared from normal cell sample. For example, the
cDNA probes from normal cells are labeled with Cy3 fluorescent dye
(green) and cDNA probes prepared from the tumor cells are labeled
with Cy5 fluorescent dye (red).
[0117] The differential expression assay is performed by probing
equal amounts of probes from tumor cells and normal cells of the
same patient. The fluorescently labeled probes are hybridized to
the array under conditions of high stringency (overnight at
42.degree. C. in 50% formamide, 5.times.SSC, and 0.2% SDS). After
hybridization, the array is washed at 55.degree. C. three times as
follows: 1) first wash in 1.times.SSC/0.2% SDS; 2) second wash in
0.1.times.SSC/0.2% SDS; and 3) third wash in 0.1.times.SSC.
[0118] The arrays are then scanned for green and red fluorescence
using a laser-scanner/detector. The images are processed using
BioDiscovery Autogene software, and the data from each scan set
normalized. The experiment is repeated, this time labeling the two
probes with the opposite color in order to perform the assay in
both "color directions." Each experiment is sometimes repeated with
two more slides (one in each color direction). The data from each
scan is normalized, and the level fluorescence for each sequence on
the array expressed as a ratio of the geometric mean of 8 replicate
spots/genes from the four arrays or 4 replicate spots/gene from 2
arrays or some other permutation.
Example 4
Detailed Embodiment with Optional Second Round
[0119] Synthesis of the First cDNA Strand
[0120] A RNA sample (of about 5 ng RNA) containing one or more
target mRNAs of interest is prepared in a small (e.g. about 5 to
about 20 .mu.L volume of water in a small tube. A first
oligonucleotide primer (from about 5 ng to about 25 or about 50 or
about 75 ng) comprising a poly dT region and one strand of a RNA
polymerase promoter region coupled to the 5' end of the poly dT
region (such that if made duplex with the complementary strand, the
promoter would initiate transcription that proceeds in the 5' to 3'
direction of the poly dT region) is added to the RNA sample. The
sample is briefly heated (e.g. from about 65-99.degree. C.) for a
short period (e.g. from about 5 to about 15 minutes) followed by
chilling on ice or at about 4.degree. C. until ready for use.
[0121] The sample is then adjusted to conditions for reverse
transcription, and reverse transcriptase activity, optionally
including endogenous RNase H activity and RNase inhibitors, is
added while maintaining the mixture in a small volume. The reaction
mixture is then incubated (e.g. from about 37 to about 45.degree.
C.) for about 1 hour followed by heating (e.g. from about
65-99.degree. C.) for a short period (e.g. from about 5 to about 15
minutes). The synthesis of the first strands of cDNA corresponding
to target mRNAs is completed at this point, and reverse
transcriptase activity is inactivated by heating. In preferred
embodiments where exonuclease is used to degrade primers after
reverse transcription, the heating is preferably from about
65-70.degree. C. to prevent denaturation of duplex nucleic acids
before the exonuclease treatment. The mixture is then chilled on
ice or at about 4.degree. C. for a short period.
[0122] In preferred embodiments where unused primers are degraded,
a small volume containing exonuclease I or other single stranded
DNA exonuclease activity (for example, but not limited to, about
20-60 units of E. coli exonuclease I activity) is added to the
reaction mixture followed by incubation at about 37.degree. C. for
about 5 to about 30 minutes. The reaction mixture is then heated at
high temperature (e.g. from about 95-99.degree. C.) for a short
period (e.g. from about 5 to about 15 minutes) to inactivate
enzymatic activities and denature duplex nucleic acids. The mixture
is then chilled on ice or at about 4.degree. C. until ready for
use. It should be noted that any duplex nucleic acids that formed
as a result of reverse transcriptase activity has been rendered
completely denatured by high temperature heating.
[0123] Synthesis of the Second cDNA Strand
[0124] Random primers are added to the above chilled mixture
followed by heating at high temperature (e.g. from about
95-99.degree. C.) for a short period (e.g. from about 2 to about 10
minutes) followed by cooling on ice or at about 4.degree. C. for a
short period (e.g. from about 2 to about 10 minutes). The mixture
is then adjusted to conditions for DNA dependent DNA synthesis, and
DNA polymerase activity, preferably a combination of Taq polymerase
and exo.sup.- Klenow is added. DNA synthesis may then proceed under
multiple incubation conditions (e.g. about 25.degree. C. or room
temperature for about 10 minutes followed by about 37.degree. C.
for about 30 minutes followed optionally by about 70 or 72.degree.
C. for about 15 minutes). The reaction is then cooled on ice or at
about 4.degree. C. until ready to proceed. The synthesis of double
stranded cDNA is complete at this point.
[0125] The cDNA may be optionally purified by any means known in
the art. In this embodiment of the invention, the cDNA is purified
by use of a spin column. Briefly, the reaction mixture is combined
with a volume of column buffer and added to a prepped column. The
column is centrifuged briefly and the flow-through discarded. A
wash buffer is added and the column centrifuged again with the flow
through discarded again. Finally, a volume of elution buffer is
added and the column spun once more with collection and retention
of the eluate as containing the cDNA. The eluate may be further
concentrated to place the cDNA into a smaller volume.
[0126] RNA Amplification/In Vitro Transcription
[0127] The cDNA from the above reaction (or a sample thereof) is
made to be in a solution under conditions suitable for in vitro
transcription, and an RNA polymerase capable of initiating
transcription from the promoter region present in the first
oligonucleotide primer (described above) is added. The reaction is
then incubated (e.g. from about 37 to about 45.degree. C.) for
about 2 to about 4 or about 6 hours.
[0128] Optionally, RNase free DNase may be added to degrade the
cDNA template prior to further use. The resultant (transcribed)
amplified RNA may be optionally purified, such as by the use of a
spin column analogous to that described above, and then
concentrated. The resultant amplified RNA may be used to prepare
labeled cDNA or used optionally as the starting material for a
second round of amplification.
[0129] Second Round
[0130] The second round begins with the addition of random primers
followed by heating (e.g. from about 70 to about 80.degree. C.) for
a short period (e.g. from about 5 to about 15 minutes) followed by
cooling on ice or at about 4.degree. C. for a short period (e.g.
from about 1 to about 10 minutes). The mixture is then adjusted to
conditions for reverse transcription, and reverse transcriptase
activity, optionally including endogenous RNase H activity and
RNase inhibitors, is added. The reaction mixture is then incubated
(e.g. from about 25 to about 37.degree. C., optionally in two
steps) for about 10 to about 90 minutes followed by heating (e.g.
from about 65-99.degree. C.) for a short period (e.g. from about 5
to about 15 minutes). The synthesis of the first strands of cDNA
corresponding to the amplified RNAs is completed at this point, and
reverse transcriptase activity may be inactivated by heating. The
mixture is then chilled on ice or at about 4.degree. C. for a short
or indefinite period.
[0131] The first oligonucleotide primer (described above) is then
added to the mixture followed by heating at a high temperature
(e.g. about 95-99.degree. C.) for a short period (e.g. from about 2
to about 15 minutes). The mixture is again chilled on ice or at
about 4.degree. C. for a short period followed by adjustment of the
mixture to be suitable for DNA dependent DNA synthesis. DNA
polymerase activity, preferably a combination of Taq polymerase and
exo.sup.- Klenow is added, and DNA synthesis allowed to proceed
under multiple incubation conditions (e.g. about 37.degree. C. for
about 30 minutes followed by about 70.degree. C. for about 15
minutes). The reaction is then cooled on ice or at about 4.degree.
C. until ready to proceed. The synthesis of double stranded DNA is
complete at this point and the DNA may be purified as described
above.
[0132] The purified DNA may then be used for RNA amplification (in
vitro transcription), and subsequent RNA purification and use, as
described above.
[0133] All references cited herein, including patents, patent
applications, and publications, are hereby incorporated by
reference in their entireties, whether previously specifically
incorporated or not, for all purposes. Citation of any reference
herein is not intended as an admission that any of the foregoing is
pertinent prior art, nor does it constitute any admission as to the
contents or date of these documents.
[0134] Having now fully described this invention, it will be
appreciated by those skilled in the art that the same can be
performed within a wide range of equivalent parameters,
concentrations, and conditions without departing from the spirit
and scope of the invention and without undue experimentation.
[0135] While this invention has been described in connection with
specific embodiments thereof, it will be understood that it is
capable of further modifications. This application is intended to
cover any variations, uses, or adaptations of the invention
following, in general, the principles of the invention and
including such departures from the present disclosure as come
within known or customary practice within the art to which the
invention pertains and as may be applied to the essential features
hereinbefore set forth.
Sequence CWU 1
1
1143DNAArtificial SequencePart of the M13 forward priming site
1aaacgacggc cactgaattg taatacgact cactataggg aga 43
* * * * *