Methods for detection of nucleotide modification
This invention relates to the identification of modified cytosine residues, such as 5-methylcytosine (5mC), 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC) to be distinguished from cytosine (C) in a sample nucleotide sequence. Methods may comprise oxidizing or reducing a first portion of polynucleotides which comprise the sample nucleotide sequence; treating the oxidized or reduced first portion and a second portion of polynucleotides with bisulfite; sequencing the polynucleotides in the first and second portions of the population following steps ii) and iii) to produce first and second nucleotide sequences, respectively and; identifying the residue in the first and second nucleotide sequences which corresponds to a cytosine residue in the sample nucleotide sequence. These methods may be useful, for example in the analysis of genomic DNA and/or of RNA.
1. A method of identifying a modified cytosine residue in a sample nucleotide sequence comprising the steps of:
(i) providing a population of polynucleotides which comprise the sample nucleotide sequence,
(ii) oxidising or reducing a first portion of said population,
(iii) treating the oxidised or reduced first portion of said population and a second portion of said population with bisulfite,
(iv) sequencing the polynucleotides in the first and second portions of the population following steps (ii) and (iii) to produce first and second nucleotide sequences, respectively, and
(v) identifying a residue in the first and second nucleotide sequences which corresponds to a cytosine residue in the sample nucleotide sequence.
2. A method according to claim 1 wherein the modified cytosine residue is 5-methylcytosine, 5-hydroxymethylcytosine or 5-formylcytosine.
3. A method according to claim 1 wherein the first portion of said population is oxidised in step (ii).
4. A method according to claim 3 wherein said oxidation selectively oxidises 5-hydroxymethylcytosine residues.
5. A method according to claim 3 wherein step (ii) comprises multiple steps of oxidation of the first portion of said population.
6. A method according to claim 3 wherein the first portion is oxidised using a chemical oxidising agent.
7. A method according to claim 3 wherein the first portion is oxidised using a perruthenate oxidising agent.
8. A method according to claim 3 wherein the first portion is oxidised using KRuO 4 .
9. A method according to claim 3 wherein identification of uracil at a position in the first nucleotide sequence which corresponds to a cytosine residue in the sample nucleotide sequence and cytosine at the same position in the second nucleotide sequence is indicative that the cytosine residue in the sample nucleotide sequence is 5-hydroxylmethylcytosine.
10. A method according to claim 3 wherein identification of cytosine at a position in both the first and second nucleotide sequences which corresponds to a cytosine residue in the sample nucleotide sequence is indicative that the cytosine residue in the sample nucleotide sequence is 5-methylcytosine.
11. A method according to claim 3 wherein identification of cytosine at a position in the first nucleotide sequence which corresponds to a cytosine residue in the sample nucleotide sequence is indicative that the cytosine residue in the sample nucleotide sequence is 5-methylcytosine.
12. A method according to claim 3 further comprising the steps of:
(vi) reducing a third portion of the population of polynucleotides comprising the sample nucleotide sequence,
(vii) treating the reduced third portion of the population with bisulfite,
(viii) sequencing the polynucleotides in the third portion following steps (vi) and (vii) to produce a third nucleotide sequence, and
(ix) identifying a residue in the third nucleotide sequence which corresponds to a cytosine residue in the sample nucleotide sequence.
13. A method according to claim 12 wherein identification of uracil at a position in the first and second nucleotide sequences which corresponds to a cytosine residue in the sample nucleotide sequence and a cytosine at this position in the third nucleotide sequence is indicative that the cytosine residue in the sample nucleotide sequence is 5-formylcytosine.
14. A method according to claim 1 wherein the first portion of said population is reduced in step (ii).
15. A method according to claim 14 wherein the first portion of said population is reduced using NaBH 4 .
16. A method according to claim 14 wherein identification of cytosine at a position in the first nucleotide sequence which corresponds to a cytosine residue in the sample nucleotide sequence and uracil at the same position in the second nucleotide sequence is indicative that the cytosine residue in the sample nucleotide sequence is 5-formylcytosine.
17. A method according to claim 14 wherein identification of uracil at a position in both the first and the second nucleotide sequence which corresponds to a cytosine residue in the sample nucleotide sequence is indicative that the cytosine residue in the sample nucleotide sequence is unmodified cytosine.
18. A method according to claim 12 comprising;
providing a fourth portion of the population of polynucleotides comprising the sample nucleotide sequence; and,
sequencing the polynucleotides in the fourth portion to produce the sample nucleotide sequence.
19. A method of identifying 5-methylcytosine in a sample nucleotide sequence comprising the steps of:
(i) providing a population of polynucleotides which comprise the sample nucleotide sequence,
(ii) oxidising said population of polynucleotides,
(iii) treating the oxidised population of polynucleotides with bisulfite to generate an oxidised, bisulfite treated population of polynucleotides,
(iv) sequencing the polynucleotides in the oxidised, bisulfite treated population to produce a treated nucleotide sequence, and
(v) identifying a residue in the treated nucleotide sequence which corresponds to a cytosine residue in the sample nucleotide sequence,
wherein the presence of a cytosine in the treated nucleotide sequence is indicative that the cytosine residue in the sample nucleotide sequence is 5-methylcytosine.
20. A method according to claim 1 wherein the polynucleotides are genomic DNA.
21. A method according to claim 20 wherein the genomic DNA is mammalian genomic DNA.
22. A method according to claim 1 wherein the polynucleotides are RNA.
23. A method according to claim 22 wherein the RNA is genomic RNA, mRNA, tRNA, rRNA or non-coding RNA.
24. A method according to claim 23 wherein the genomic RNA is mammalian, plant or viral genomic RNA.
25. A method according to claim 18 wherein the population of polynucleotides or one or more of the first, second, third and fourth portions of the population are immobilised.
26. A method according to claim 18 wherein one or more of the first, second, third and fourth portions of the population are amplified before sequencing.
27. A method according to claim 26 wherein one or more of the first, second, and third portions of the population are amplified following treatment with bisulfite.