Methods for creating directional bisulfite-converted nucleic acid libraries for next generation sequencing
Provided herein are methods, compositions and kits for the generation of bisulfite-converted next generation sequencing (NGS) libraries. The methods, compositions and kits provided herein can be useful, for example, for the production of libraries from genomic DNA that allow for determination of the methylation status across the genome, i.e. the methylome. The methods, compositions and kits provided herein can also be utilized to query methylation status at a particular genomic locus or loci. Moreover, the methods provided herein can be employed for high-throughput sequencing of bisulfite-converted DNA while maintaining the directional (strandedness) information of the original nucleic acid sample.
1. A method for generating a nucleic acid library, the method comprising:
ligating first strands of oligonucleotide adapters of similar construct to 5′ ends of double-stranded DNA fragments in a sample, wherein the first strand of each adapter comprises one or more guanine;
extending 3′ ends of the double-stranded DNA fragments with a DNA polymerase in the presence of a dCTP analog resistant to bisulfite treatment, thereby creating extension products comprising one or more cytosines resistant to bisulfite treatment and complementary to the guanines;
treating the extension products with bisulfite, thereby converting unmodified cytosines bases in the DNA fragments and adapter sequences to uracil; and
amplifying the bisulfite-treated extension products.
2. The method of claim 1 , wherein prior to treating the extension product with bisulfite, the extension product is denatured.
3. The method of claim 2 , wherein the denaturing step generates a single-stranded DNA fragment comprising the sequence of a first strand of a ligated adapter at the 5′ end and a sequence complementary to a first strand of a ligated adapter at the 3′ end.
4. The method of claim 3 , wherein the oligonucleotide adapters have the same sequence.
5. The method of claim 4 , wherein the amplifying step includes contacting the bisulfite treated extension products with a first primer, wherein the first primer is directed against a sequence complementary to the first strand of the adapters which comprise uracil bases following the bisulfite treatment.
6. The method of claim 5 , wherein the amplifying step further includes contacting the bisulfite treated extension products with a second primer, wherein the second primer is directed against a sequence complementary to the first strand of the adapters.
7. The method of claim 6 , wherein the first and/or second primer comprise a barcode sequence.
8. The method of claim 7 , wherein the first and/or second primer comprise a non-hybridizable tail.
9. The method of claim 8 , wherein the non-hybridizable tail comprises the barcode sequence, a flow cell sequence, and/or an index sequence.
10. The method of claim 9 , wherein the index sequence is a primer sequence compatible with a next generation sequencing platform.
11. The method of claim 1 , further comprising sequencing amplicons of the amplified bisulfite-treated extension products.
12. The method of claim 1 , wherein the adapters are duplex adapters.
13. The method of claim 12 , wherein the adapters comprise a second strand that is incapable of ligation to the 3′ end of the double-stranded DNA fragments.
14. The method of claim 13 , wherein a 5′ end of the second strand comprises a biotin moiety.
15. The method of claim 13 , wherein a 3′ end of the second strand comprises a terminal dideoxycytosine.
16. The method of claim 1 , wherein the adapters are partial duplex adapters, wherein each adapter comprises the first strand and a second strand.
17. The method of claim 16 , wherein a long strand of the partial duplex is the first strand and a shorter strand of the partial duplex is the second strand.
18. The method of claim 1 , wherein the dCTP analog resistant to bisulfite treatment is 5-methyl dCTP, 5-hydroxymethyl dCTP, or 5-propynyl dCTP.
19. The method of claim 1 , further comprising before the bisulfite treatment, performing methylcytosine capture, wherein the dCTP analog is a cytosine analog other than 5-methyl dCTP.
20. The method of claim 19 , wherein the methylcytosine capture is performed using a methylcytosine binding protein or an anti-methylcytosine antibody.