Reversible methylation of DNA through maternal and patterning imprinting, as well as re-organization of methylation during embryogenesis and post-natal development, represents a canonical mechanism for epigenetic control. Active methylation (5-mC) is established by DNA methyl transferases (DNMTs) and so-called TET proteins that mediate DNA demethylation and generate several stable intermediates that generate a DNA methylome code (i.e., 5-mC, 5-hmC, 5-fC and 5-caC).