Oxidized form of 5-methylcytosine—5-hydroxymethylcytosine: a new insight into the biological significance in the mammalian genome

In this review, we summarize data on 5-hydroxymethylcytosine—a modification of cytosine with a recently discovered epigenetic effect. We discuss the biochemical mechanisms of 5-hydroxymethylcytosine generation and further modification in the mammalian genome, analyze the role of 5-hydroxymethylcytosine in the epigenetic reprogramming during mammalian gametogenesis and early embryogenesis as well as in the regulation of gene expression. We also show recent data on the diseases and the adverse environmental factors, linked to the DNA hydroxymethylation disruptions.