Digital Counting of Individual Molecules by Stochastic Attachment of Diverse Labels
Compositions, methods and kits are disclosed for high-sensitivity single molecule digital counting by the stochastic labeling of a collection of identical molecules by attachment of a diverse set of labels. Each copy of a molecule randomly chooses from a non-depleting reservoir of diverse labels. Detection may be by a variety of methods including hybridization based or sequencing. Molecules that would otherwise be identical in information content can be labeled to create a separately detectable product that is unique or approximately unique in a collection. This stochastic transformation relaxes the problem of counting molecules from one of locating and identifying identical molecules to a series of binary digital questions detecting whether preprogrammed labels are present. The methods may be used, for example, to estimate the number of separate molecules of a given type or types within a sample.
1 . A method of determining a presence of an allele of a polymorphic site in a tagged genomic sample, the method comprising:
a) amplifying a population of different target DNA molecules from a tagged genomic sample thereby producing a population of amplified target DNA molecules, wherein:
(i) the different target DNA molecules that comprise a polymorphic site are tagged with different label-tags;
(ii) the label-tags comprise nucleotide bases selected from purine bases, pyrimidine bases, natural nucleotide bases, chemically modified nucleotide bases, biochemically modified nucleotide bases, non-natural nucleotide bases and derivatized nucleotide bases; and
(iii) the amplified target DNA molecules comprise the polymorphic site and an associated label-tag of the label-tags;
b) detecting the population of amplified labeled-targets by sequencing, thereby producing a plurality of readouts,
wherein the plurality of readouts comprise (i) the nucleotide sequence of at least a portion of the polymorphic site and (ii) the nucleotide sequence of an associated label-tag; and
c) assessing, using a computer, the presence of the allele in the tagged genomic sample, based on:
(i) a determination of a number of the different label-tags that are associated with the allele; and
(ii) a determination of a number of readouts that comprise each of the different label-tags that are associated with the allele.
2 . The method of claim 1 , wherein the assessing step c) further comprises independently assessing the presence of an additional allele of the polymorphic site in the tagged genomic sample based on:
(i) a determination of a number of the different label-tags that are associated with the additional allele of the polymorphic site; and
(ii) a determination of a number of readouts that comprise each of the different label-tags that are associated with the additional allele.
3 . The method of claim 1 , wherein the population of different target DNA molecules is produced by ligating a set of adaptors that comprise the label-tags to an initial nucleic acid sample.
4 . The method of claim 3 , wherein the initial nucleic acid sample is an amplification product.
5 . The method of claim 1 , wherein the population of different target DNA molecules is produced by primer extension of a set of primers that comprises the label-tag, using an initial nucleic acid sample as a template.
6 . The method of claim 5 , wherein the initial nucleic acid sample is an amplification product.
7 . The method of claim 1 , wherein the method comprises, prior to the amplifying step (a), enriching the population of different target DNA molecules from an initial nucleic acid sample.
8 . The method of claim 1 , wherein the label-tags comprise at least 2 nucleotide bases, wherein each of the at least 2 nucleotide bases are selected from purine bases, pyrimidine bases, natural nucleotide bases, chemically modified nucleotide bases, biochemically modified nucleotide bases, non-natural nucleotide bases and derivatized nucleotide bases.
9 . The method of claim 8 , wherein the label-tags comprise from 2 to 20 nucleotide bases, wherein each of the 2 to 20 nucleotide bases is selected from purine bases, pyrimidine bases, natural nucleotide bases, chemically modified nucleotide bases, biochemically modified nucleotide bases, non-natural nucleotide bases and derivatized nucleotide bases.
10 . The method of claim 1 , wherein the label-tag is used to correct estimation errors.
11 . The method claim 1 , wherein the different target DNA molecules are further tagged with a unique sequence tag that is used to distinguish target DNA molecules from different samples.
12 . The method of claim 11 , wherein the tagged genomic sample is a mixed sample comprising nucleic acid molecules from different samples, wherein each of the samples is associated with a unique sequence tag that distinguishes the sample of the target DNA molecules to which it is tagged.
13 . The method of claim 12 , wherein each of the samples is derived from a human subject.
14 . The method of claim 12 , wherein each of the samples is derived from a tumor cell.
15 . The method of claim 1 , wherein the tagged genomic sample comprises polynucleotides from a tumor cell.
16 . The method of claim 1 , wherein the tagged genomic sample comprises polynucleotides from bacteria.
17 . The method of claim 1 , wherein the tagged genomic sample comprises human genomic DNA and the polymorphic site comprises a single nucleotide polymorphism of a human genome.
18 . The method of claim 1 , wherein the detecting the population of amplified labeled-targets by sequencing step b) comprises sequencing the amplified target DNA molecules by next-generation sequencing.
19 . The method of claim 1 , wherein the amplifying step a) is done by polymerase chain reaction.
20 . The method of claim 1 , wherein the assessing of step c) comprises performing a statistical analysis.
21 . The method of claim 1 , wherein the method further comprises determining the amount of the allele in the tagged genomic sample.
22 . A method for assessing the presence of an allele of a polymorphic target sequence in a tagged genomic sample, comprising:
a) amplifying a population of different initial target DNA molecules from a tagged genomic sample thereby producing a population of amplified target DNA molecules, wherein the different initial target DNA molecules that comprise a polymorphic target sequence are tagged with different degenerate base region (DBR) sequences, wherein said DBR sequences comprises at least one nucleotide base selected from: R, Y, S, W, K, M, B, D, H, V, N and modified versions thereof and wherein the amplified target DNA molecules comprise said polymorphic target sequence and an associated DBR sequence of said DBR sequences;
b) sequencing a plurality of the amplified target DNA molecules, thereby producing a plurality of sequence reads, wherein the sequencing step provides, for each of the amplified target DNA molecules that are sequenced:
(i) the nucleotide sequence of at least a portion of the polymorphic target sequence and
(ii) the nucleotide sequence of an associated DBR sequence;
c) assessing, using a computer, the presence of said allele in said tagged genomic sample, based on:
(i) a determination of the number of said different DBR sequences that are associated with said allele; and
(ii) a determination of the number of said sequence reads that comprise each of the different DBR sequences that are associated with said allele.
23 . The method of claim 22 , wherein: said assessing step c) further comprises independently assessing the presence of an additional allele of the polymorphic target sequence in said tagged genomic sample based on: (i) a determination of the number of said different DBR sequences that are associated with the additional allele of said polymorphic target sequence; and (ii) a determination of the number of said sequence reads that comprise each of the different DBR sequences that are associated with the additional allele.
24 . The method of claim 22 , wherein said population of different initial target DNA molecules is made by ligating a set of adaptors that comprise said DBR sequences to an initial nucleic acid sample.
25 . The method of claim 24 , wherein said initial nucleic acid sample is an amplification product.
26 . The method of claim 22 , wherein said population of different initial target DNA molecules is made by primer extension of a set of primers that comprises said DBR sequences, using an initial nucleic acid sample as a template.
27 . The method of claim 26 , wherein said initial nucleic acid sample is an amplification product.
28 . The method of claim 22 , wherein the method comprises, prior to said amplifying step (a), enriching said population of different initial DNA molecules from an initial nucleic acid sample.
29 . The method of claim 22 , wherein said DBR sequences comprise at least 2 nucleotide bases, wherein each of the at least 2 nucleotide bases are selected from: R, Y, S, W, K, M, B, D, H, V, N, and modified versions thereof.
30 . The method of claim 29 , wherein the DBR sequences comprise from 3 to 20 nucleotide bases, wherein each of the 3 to 10 nucleotide bases is selected from: R, Y, S, W, K, M, B, D, H, V, N, and modified versions thereof.
31 . The method of claim 22 , wherein said DBR sequences comprise an error-correcting code.
32 . The method of claim 22 , wherein the different initial target DNA molecules are further tagged with a unique multiplex identifier (MID) sequence that identifies the source of a nucleic acid molecule to which it is tagged.
33 . The method of claim 32 , wherein said tagged genomic sample is a pooled sample comprising nucleic acid molecules from several different sources, wherein each of said sources is associated with a unique MID sequence that identifies the source of the nucleic acid molecule to which it is tagged.
34 . The method of claim 33 , wherein each of the sources is derived from a human subject.
35 . The method of claim 33 , wherein each of the sources is derived from different parts of a tumor.
36 . The method of claim 33 , wherein each of the sources is derived from a subject at different times.
37 . The method of claim 22 , wherein the tagged genomic sample comprises polynucleotides from a tumor.
38 . The method of claim 22 , wherein the tagged genomic sample comprises polynucleotides from a microorganism and/or a virus.
39 . The method of claim 22 , wherein the tagged genomic sample comprises human genomic DNA and said polymorphic target sequence comprises a single nucleotide polymorphism of a human genome.
40 . The method of claim 22 , wherein said sequencing step b) comprises sequencing said plurality of amplified target DNA molecules on a next-generation sequencing platform.
41 . The method of claim 22 , wherein the amplifying step a) is done by polymerase chain reaction.
42 . The method of claim 22 , wherein the method further assessing step c) comprises performing a maximum likelihood analysis.
43 . The method of claim 22 , wherein the method further comprises determining the amount of the allele in the tagged genomic sample.