DNMT1 and obesity due to melanocortin 4 receptor deficiency: However, similar to the discussion for imprinted genes, no significant increase in DNMT expression was evident in the HE-HE group, suggesting that any effects at the oocyte level or before day 7 of embryo development only become apparent when the embryo is exposed to an environment that does not meet its expectations or after a longer period of exposure to maternal overnutrition or obesity.