Mammalian fetal ovaries contains numerous primordial germ cells, however fewer ones can yield mature oocytes due to apoptosis and follicle atresia. Successful in vitro reconstitution of primordial germ cells has recently had a significant effect in the field of assisted reproductive technologies. However, the regulatory mechanisms underlying oogenesis remain unknown and recapitulation of oogenesis in vitro remains unachieved. Therefore, development of methods for obtaining mature oocytes by culturing the fetal ovaries in vitro could contribute to clarify these mechanisms. We adapt an in vitro system for culturing mouse fetal ovaries that support successful follicle assembly and improve oocyte growth and maturation. Ovarian tissues from 12.5 days postcoitum (dpc) fetal mice were cultured in vitro and the matured oocytes were differentiated from primordial germ cells after a 31 days culture period. Our results demonstrate that mouse fetal germ cells are able to form primordial follicles with artificial ovarian cells, and that oocytes within the growing follicles are able to mature normally in vitro. Taken together, this in vitro culture system is expected to aid in the development of new strategies to identify the reasons behind failure of follicle assembly and offer a platform for innovative research into preservation of female germ cells and conservation of endangered species.

Previous studies have shown that kisspeptin (Kp-10) is expressed in mammalian ovaries; however, the expression and role of Kp-10 in bovine ovarian granulosa cells are still unclear. In this study, we assessed the expression of Kp-10 and its effects on the proliferation and apoptosis of bovine granulosa cells. Immunohistochemical analysis showed that Kp-10 was expressed in the cytoplasm of bovine ovarian granulosa cells. Moreover, MTT (3-[4,5-dimethyl-2-thiazolyl]-2,5-diphenyl-2- H-tetrazolium bromide) assays showed that 100 nM Kp-10 significantly inhibited the viability of granulosa cells (P<0.01). Flow cytometry analysis showed that Kp-10 could significantly increase accumulation of cells in the G1 phase, decrease accumulation of cells in the S phase, and promote apoptosis in bovine granulosa cells (P<0.05). Additionally, Kp-10 decreased the mRNA levels of Bcl-2, an anti-apoptotic gene; increased the mRNA levels of caspase-3, a pro-apoptotic gene; and increased the mRNA levels of Fas and Fasl, two membrane surface molecule genes (P<0.05). Thus, our findings demonstrated for the first time that Kp-10 inhibited proliferation and promoted apoptosis in bovine ovarian granulosa cells. These findings provide insights into our understanding of the role of Kp-10 in mediating the proliferation of bovine granulosa cells.