RIF1 and obesity due to melanocortin 4 receptor deficiency: In this study, we conducted a comprehensive and detailed phenotypic assessment of oocytes and preimplantation embryos induced by the maternal obesity, and identified that RIF1 could act as a maternal epigenetic factor related to DNA stress damage and that its overexpression can mediate metabolic phenotypic differences by regulating epigenetic modifications on MuERV-L in obese mice, which could be partially rescued by metformin treatment.