Getting rid of DNA methylation

• DNA methylation is a widespread epigenetic trait that is remodeled during development.
• Multiple routes for DNA demethylation exist across the animal and plant kingdoms.
• 5mC removal from the genome requires DNA synthesis-dependent and -independent processes.
• Tet proteins convert 5mC to 5hmC, an intermediate in active and passive demethylation.

Methylation of cytosine within DNA is associated with transcriptional repression and genome surveillance. In plants and animals, conserved pathways exist to establish and maintain this epigenetic mark. Mechanisms underlining its removal are, however, diverse and controversial and can depend on DNA synthesis (passive) or be independent of it (active). Ten–eleven translocation (Tet)-mediated conversion of 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC) has recently been evoked as a possible mechanism in the initiation of active and passive DNA demethylation. This review discuses the recent progress in this exciting area.