Methods and compositions for generating and amplifying DNA libraries for sensitive detection and analysis of DNA methylation
The present invention regards a variety of methods and compositions for obtaining epigenetic information, such as DNA methylation patterns, through the preparation, amplification and analysis of Methylome libraries. In particular, the method employs preparation of a DNA molecule by digesting the DNA molecule with at least one methylation-sensitive restriction enzyme; incorporating a nucleic acid molecule into at least some of the digested DNA molecules by either (1) incorporating at least one primer from a plurality of primers that have a 5′ constant sequence and a 3′ variable sequence, wherein the primers are substantially non-self-complementary and substantially non-complementary to other primers in the plurality; or (2) incorporating an oligonucleotide having an inverted repeat and a loop under conditions wherein the oligonucleotide becomes blunt-end ligated to one strand of the digested DNA molecule, followed by polymerization from a 3′ hydroxyl group present in a nick in the oligonucleotide-linked molecule; and amplifying one or more of the DNA molecules.
1. A method of preparing a DNA molecule, comprising the steps of:
(1) providing a DNA molecule;
(2) providing an oligonucleotide-linked DNA molecule in a single incubation, said single incubation comprising:
(a) modifying the ends of the DNA molecule to provide attachable ends;
(b) ligating a first oligonucleotide comprising a known sequence and a nonblocked 3, end to an end of the DNA molecule to produce an oligonucleotide-linked molecule, wherein the 5′ end of the DNA molecule is attached to the nonblocked 3, end of the first oligonucleotide, leaving a nick site between a juxtaposed 3′ end of the DNA molecule and a 5′ end of the first oligonucleotide; and
(c) extending the juxtaposed 3, end of the DNA molecule from the nick site by polymerization;
(3) digesting the oligonucleotide-linked molecule with a mixture of methylation-sensitive restriction enzymes that do not cleave within the first oligonucleotide of the oligonucleotide-linked molecule; and
(4) amplifying the digested oligonucleotide-linked molecule with a primer complementary to at least a portion of the known sequence of the first oligonucleotide to produce amplified oligonucleotide-linked molecules.
2. The method of claim 1 , further comprising the step of determining at least part of the sequence of the amplified oligonucleotide-linked molecules.
3. The method of claim 1 , wherein the DNA molecule is from a body fluid or a tissue.
4. The method of claim 3 , wherein the body fluid comprises blood, serum, urine, cerebrospinal fluid, nipple aspirate, sweat, or saliva.
5. The method of claim 3 , wherein the tissue comprises biopsy, surgical sample, or cheek scrapings.
6. The method of claim 1 , wherein digestion of the oligonucleotide-linked molecule with the mixture of methylation-sensitive restriction enzymes occurs during step (2).
7. The method of claim 1 , wherein the oligonucleotide-linked molecule comprises a non-replicable region in the first oligonucleotide portion.
8. The method of claim 7 , wherein the non-replicable region is generated during step (2).
9. The method of claim 7 , wherein the non-replicable region comprises at least one abasic site.
10. The method of claim 9 , wherein the at least one abasic site is generated from at least one deoxyuridine located within the non-replicable region of the first oligonucleotide.
11. The method of claim 7 , wherein the 3′ end of the DNA molecule is extended from the nick site up to the non-replicable region of the first oligonucleotide portion.
12. The method of claim 9 , wherein the amplifying step comprises a first heating step to fragment the at least one abasic region of the oligonucleotide-linked molecule.
13. The method of claim 1 , further comprising a step wherein sodium bisulfite is provided to said oligonucleotide-linked molecule, wherein any unmethylated cytosines in said oligonucleotide-linked molecule are converted to uracil, thereby producing a bisulfite-converted molecule.
14. The method of claim 1 , wherein the first oligonucleotide is further defined as comprising a 3′ stem region, wherein said 3′ stem region does not comprise guanine and wherein all cytosines are methylated.
15. The method of claim 1 , further comprising a step of enriching for oligonucleotide-linked molecules comprising CpG-rich regions.
16. The method of claim 1 , further comprising a step of comparing at least part of a sequence of the amplified oligonucleotide-linked molecules with a control DNA molecule that was not subjected to the digesting step.
17. The method of claim 6 , wherein the single incubation comprises the DNA molecule, a DNA polymerase, a DNA ligase, the first oligonucleotide, and the mixture of methylation-sensitive restriction enzymes.
18. The method of claim 1 , wherein the first oligonucleotide is a stem-loop adaptor having an inverted repeat and a loop.
19. The method of claim 18 , wherein the inverted repeat comprises a 5′ stem region and a 3′ stem region that is complementary to the 5′ stem region.
20. The method of claim 19 , wherein the first oligonucleotide comprises a non-replicable base in the loop region.
21. The method of claim 20 , wherein the first oligonucleotide further comprises a non-replicable base within the 5′ stem region.
22. The method of claim 1 , wherein the first oligonucleotide does not contain a loop.
23. The method of claim 1 , wherein the DNA molecule has been fragmented mechanically or chemically.
24. The method of claim 23 , wherein the DNA molecule has been fragmented by sonication.
25. The method of claim 1 , wherein the DNA molecule has been fragmented by enzymatic fragmentation.
26. The method of claim 1 , wherein the enzymatic fragmentation is by at least one site-specific restriction endonuclease.
27. The method of claim 1 , wherein the enzymatic fragmentation is by a random endonuclease.
28. The method of claim 1 , wherein the DNA molecule has been fragmented in vivo.
29. The method of claim 28 , wherein the DNA molecule is the product of apoptosis-induced degradation.
30. The method of claim 1 , wherein the extending of step (2)(d) comprises nick translation polymerization.
31. The method of claim 1 , wherein the extending of step (2)(d) comprises strand displacement polymerization.
32. The method of claim 1 , wherein the incubation of step (2) further comprises repairing nicks and/or gaps within the DNA molecule.