DNA unmethylome profiling by covalent capture of CpG sites

Dynamic patterns of cytosine-5 methylation and successive hydroxylation are part of epigenetic regulation in eukaryotes, including humans, which contributes to normal phenotypic variation and disease risk. Here we present an approach for the mapping of unmodified regions of the genome, which we call the unmethylome. Our technique is based on DNA methyltransferase-directed transfer of activated groups and covalent biotin tagging of unmodified CpG sites followed by affinity enrichment and interrogation on tiling microarrays or next generation sequencing. Control experiments and pilot studies of human genomic DNA from cultured cells and tissues demonstrate that, along with providing a unique cross-section through the chemical landscape of the epigenome, the methyltransferase-directed transfer of activated groups-based approach offers high precision and robustness as compared with existing affinity-based techniques. Chemical modifications of CpG dinucleotides form part of the epigenetic code and various methods for the detection of modified CpG sites exist. Here Kriukiene and colleagues report a complementary method that allows the profiling of unmodified CpG sites within the genome, which they call the 'unmethylome'.