Epigenetic reprogramming of the parental genome occurs in fertilized oocytes and involves oxidation of 5-methylcytosines (5-mC) to 5-hydroxymethylcytosines (5-hmC) in the paternal pronucleus. Recent work has shown that the maternal genome is protected from this remodeling step by an interaction between a modified histone, H3K9me2, and the oocyte-derived factor, PGC7, to prevent oxidation of the maternal DNA by the Tet3 5-methylcytosine oxidase.
