A co-culture system with preantral follicular granulosa cells in vitro induces meiotic maturation of immature oocytes

Development of technologies to mature oocytes in vitro is important for in vitro fertilization research. Here, we investigated the ability of preantral follicular granulosa cells (PAGCs) to restrain apoptosis and to promote the growth and meiotic resumption of immature murine oocytes in vitro. The oocytes of 55–65 μm derived from 12 to 14 days old juvenile mice were co-cultured with PAGCs in vitro. The results showed that the oocytes co-cultured with PAGCs for 7 days grew faster and 14.6% of immature oocytes were able to complete the first meiotic division and arrive at the MII stage. 71 oocytes co-cultured with PAGCs were fertilized and 16 embryos were able to form morula-blastocysts. Following the co-culture of immature oocytes with/without PAGCs for 7 days, the percentage of apoptotic oocytes were 33.5 and 51.4%, respectively (p < 0.01). Furthermore, the inhibition of apoptosis was communicated between oocytes and PAGCs through the GDF9-PI3 K-Akt signaling pathway. In conclusion, the co-culture with PAGCs has a beneficial effect on the growth and maturation of immature oocytes.