A genome-scale map of DNA methylation kinetics

While the first genome-wide DNA methylation map in mammalian cells was established over 10 years ago, such maps only provide snapshots and do not inform about the actual dynamics of this epigenetic mark. Researchers from the Schübeler group now quantified actual rates of methylation and demethylation for 860,404 individual CpGs in mouse embryonic stem cells. Their study reveals highly variable and context-specific activity for the DNA methylation machinery. DNA methylation is an essential epigenetic mark in eukaryotes and plays a role in gene regulation. It occurs most frequently at cytosines that are followed by guanines (CpG), where high levels of DNA methylation in promoter regions are typically associated with gene repression. DNA methylation levels are governed by opposing enzymatic reactions that apply and remove the mark. In mammalian cells, the methylation process can be divided into two types carried out by two classes of DNA methyltransferases (DNMTs): maintenance methylation (to preserve DNA methylation after every cellular DNA replication cycle) and de novo methylation (to set up DNA methylation patterns early in development).