Mirror bisulfite sequencing – a method for single-base resolution of hydroxymethylcytosine

While the role of 5-methylcytosine has been well studied, the biological role of 5-hydroxymethylcytosine still remains unclear due to the limited methods available for single-base detection of 5-hydroxymethylcytosine (5hmC). Here we present Mirror bisulfite sequencing for the detection of 5hmC at a single CpG site by synthesizing a DNA strand to mirror the parental strand. This semi-conservative duplex is sequentially treated with ß-glucosyltransferase and M.SssI methylase. A glucosyl-5hmCpG in the parental strand inhibits methylation of the mirroring CpG site, and after bisulfite conversion, a thymine in the mirroring strand indicates a 5hmCpG site in the parental strand whereas a cytosine indicates a non-5hmC site. Using this method, the 5hmC levels of various human tissues and paired tumor liver tissues were mapped genome-wide. Overall design: developing a new assay for genomic profiling of 5hmC