Hydroxymethylation of DNA: an epigenetic marker

DNA methylation, an epigenetic mechanism is claimed to play essential roles in development, aging and disease over the past few decades. Cytosines (C) were known to exist in two functional states: unmethylated or methylated (5mC) in the mammalian genome for a very long time. However, the mechanisms controlling 5mC dynamics remain undefined. Recent studies of genomic DNA on human and mouse brain, neurons and from mouse embryonic stem cells have shown that 2-oxoglutarate and Fe(II)-dependent oxygenases of the ten-eleven translocation (Tet) proteins can catalyze the oxidation of 5mC at cpG dinucleotides to form 5hydroxymethylcytosine (5-hmC). The exhilarating discovery of these novel 5-hmC has begun to focus on the dynamic nature of 5mC. The prevailing evidence has shown that Tet family proteins and 5-hmC are involved in the normal development as well as in many diseases. This review presents an overview of the role of Tet family proteins and 5-hmC. It also discusses their role as an epigenetic marker and the techniques used for their analysis.