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:
a) fragmenting double-stranded DNA, thereby generating a double-stranded DNA fragment;
b) performing end repair on the double-stranded DNA fragment, thereby generating an end repaired double-stranded DNA fragment;
c) ligating a first strand of a first adapter duplex to a first 5′ end of the end repaired double-stranded DNA fragment, wherein a second strand of the first adapter duplex is incapable of ligation to a 3′ end of the end-repaired double-stranded DNA fragment, and ligating a first strand of a second adapter duplex to a second 5′ end of the double-stranded DNA fragment, wherein the first adapter duplex and the second adapter duplex have the same sequence, wherein the first strand of each adapter comprises a guanine, thereby generating an adapter-ligated double-stranded DNA fragment;
d) extending 3′ ends of the adapter-ligated double-stranded DNA fragment with a DNA polymerase in a presence of a dCTP analog resistant to bisulfite treatment thereby generating a double-stranded DNA extension product comprising 3′ ends comprising the dCTP analog and wherein the 3′ ends are complementary to the first strands of the first adapter duplex and wherein the dCTP analog is complementary to the guanine in the first strand of the adapter;
e) denaturing the double-stranded DNA extension product, thereby creating a single-stranded DNA fragment comprising the first strand of the first adapter duplex ligated to a first 5′ end and a 3′ end comprising the dCTP analog;
f) subjecting the single-stranded DNA fragment to bisulfite treatment, wherein the bisulfite treatment converts cytosine residues to uracils in the first strand of the first adapter duplex of the single-stranded DNA fragment, thereby generating a bisulfite treated single-stranded DNA fragment comprising the first strand of the first adapter duplex comprising the uracils and the 3′ end comprising the dCTP analog;
g) extending a first oligonucleotide primer annealed to the bisulfite treated single-stranded DNA fragment wherein the first oligonucleotide primer is annealed to the 3′ end comprising the dCTP analog and wherein a guanine in the first oligonucleotide primer hybridizes with the dCTP analog in the 3 ′ end of the single-stranded DNA fragment, thereby generating a first extension product comprising sequence complementary to the first strand of the first adapter duplex comprising the uracils;
h) extending a second oligonucleotide primer annealed to the first extension product, wherein the second oligonucleotide primer is annealed to the sequence complementary to the first strand of the first adapter duplex comprising the uracils, wherein the second oligonucleotide primer has the same sequence as the first oligonucleotide primer except that the second oligonucleotide primer has an adenine at a location corresponding to the guanine in first oligonucleotide primer that hybridizes with the dCTP analog in the 3′ end of the single-stranded DNA fragment, thereby generating a second extension product; and
i) performing polymerase chain reaction (PCR) with the first oligonucleotide primer, the second oligonucleotide primer, the first extension product, and the second extension product, thereby generating a nucleic acid library comprising an amplified product.
2. The method of claim 1 , further comprising sequencing the amplified product.
3. The method of claim 1 , wherein the double-stranded DNA comprises genomic DNA.
4. The method of claim 1 , wherein a 5′ and/or 3′ end of the second strand of the first adapter duplex incapable of ligation is blocked to prevent adapter dimer formation.
5. The method of claim 1 , wherein a 3′ end of the second strand of the first adapter duplex incapable of ligation is blocked with a terminal dideoxycytosine.
6. The method of claim 1 , wherein a 5′ end of the second strand of the first adapter duplex incapable of ligation comprises a biotin moiety.
7. The method of claim 1 , wherein the first oligonucleotide primer and/or the second oligonucleotide primer comprise a barcode sequence.
8. The method of claim 1 , wherein the dCTP analog resistant to bisulfite treatment is 5-methyl dCTP.
9. The method of claim 1 , wherein the dCTP analog resistant to bisulfite treatment is 5-hydroxymethyl dCTP.
10. The method of claim 1 , wherein the dCTP analog resistant to bisulfite treatment is 5-propynyl dCTP.
11. The method of claim 1 , further comprising performing methylcytosine capture prior to step f), and wherein the dCTP analog resistant to bisulfite treatment is a cytosine analog other than 5-methyl dCTP.
12. The method of claim 11 , wherein the 5-methylcytosine capture is performed using a methylcytosine binding protein.
13. The method of claim 11 , wherein the 5-methylcytosine capture is performed using an anti-5-methylcytosine antibody.
14. The method of claim 1 , wherein the first adapter duplex is a partial duplex.
15. The method of claim 14 , wherein a long strand of the partial duplex is the first strand of the first adapter duplex and a shorter strand of the partial duplex is the second strand of the first adapter duplex.