Methylation of DNA is one of the major content of epigenetics. Methylation of DNA can change the functional state of regulatory regions, but it does not change the Watson–Crick base pairing of cytosine. Here, we will talk about the function and information content of DNA methylation in both non-vertebrates and vertebrates.
For plants and invertebrates, there are so called “mosaic’ methylation patterns because only specific genomic elements are targeted. In the case of repetitive DNA, it is evident that DNA methylation is used for repressing expression and preventing further expansion of these elements.
In vertebrates, heritable methylation only occurs at the CpG dinucleotide. Sequence symmetry of CpGs enables propagation of the methyl mark through cell division.
DNA methylation is set up by DNMTs. Mutations in DNMT3A are pre-leukaemic and can occur in blood stem cells, but only in combination with subsequent ‘driver mutations’ lead to leukaemia. Genomic maps of DNA methylation have revealed unexpected dynamics at gene regulatory regions, including active demethylation by TET proteins at binding sites for transcription factors.
A better understanding of DNA methylation is required to define these potential functions and determine how misregulation contributes to disease.