Double-stranded methylation can be long-lived. In the event that one mC is damaged, metab-
olized, or excised to yield an unsubsidized cytosine, the memory of the mark is not necessarily lost
and can be reestablished by maintenance DNMT activity. Indeed, it is by this mechanism that
dividing cells pass down their methyl marks to their progeny. That is not to say demethylation
cannot occur, and active CpG demethylation mechanisms have been an ongoing area of research
(12). Ten-eleven translocation (Tet) mC dioxygenases oxidize the benzylic position of mC to