GPR3 cDNA was first isolate from a rat insulinoma cell line and a human neuroblastoma cDNA library. It expresses in low abundance predominantly in the central nervous system and at low levels in lung and kidney. GPR3 is involved in maintaining meiotic arrest in mammalian oocytes. Oocytes from GPR3 knockout mice resumed meiosis within antral follicles, independently of an increase in luteinizing hormone. In GPR3-null mice, progressive reduction in litter size was observed. Aging GPR3-null mice had severe reduction of fertility, manifested by an increasing number of nondeveloping early embryos upon spontaneous ovulation and massive amounts of fragmented oocytes after superovulation. Based on the above evidence, it was concluded that GPR3 plays a role in the protection or rescue of oocytes from aging.