Is DNA methylation reversible?

Yes, DNA methylation is a reversible process that can occur actively or passively in mammals.

• Active DNA demethylation refers to the direct removal of a methyl group from 5-methylcytosine via an enzymatic process. For example, ten-eleven translocation (TET) methylcytosine dioxygenases are a family of enzymes that catalyze the stepwise oxidation of methylated cytosine in DNA to 5-hydroxymethylcyotsine, which is further oxidize to 5-formylcytosine (5fC) and 5-carboxycytosine (5caC). Through base excision repair cells remove these oxidation products so that it can be replaced by cytosine.
• Passive DNA demethylation refers to the reduction of methylated cytosine during successive cycles of DNA replication without DNMT1and UHRF1present.