The ten-eleven translocation (Tet) family of methylcytosine dioxygenases, which includes Tet1, Tet2, and Tet3 enzymes, has been recently implicated in DNA demethylation it converts 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) as well as to 5-formylcytosine and 5-carboxylcytosine (Tahiliani et al., 2009; Ito et al., 2010; Guo et al., 2011a). 5hmC has been proposed to act as an intermediate in demethylation and the base-excision repair machinery (Guo et al., 2011a).