




DNA methylation is a key epigenetic mechanism implicated in transcriptional regulation, normal cellular development, and function. The addition of methyl groups that occurs mostly within CpG dinucleotides is catalyzed by three major DNA methyltransferase (DNMT) family members: DNMT1, DNMT3a, and DNMT3b.
CpG dinucleotides, which are under-represented in the genome, are concentrated in CpG islands (CGI). While most CpGs in the genome are methylated, CGI are not. Importantly, most CGI are located within promoter and transcription start sites of protein coding genes the expression of which is influenced by the methylation status of those CGI. As a matter of fact, methylated CGI are associated with silenced genes whereas unmethylated CGI are associated with expressed genes.