Contribution of zona pellucida proteins to ovarian folliculogenesis

The zona pellucida (ZP) surrounding the mammalian oocyte plays an important roles during fertilization and pre-implantation embryo development. In this study, we examined whether the mouse ZP components of ZP1, ZP2 and ZP3 are involved in follicular development using RNA interference (RNAi) techniques. Premature follicles were collected from juvenile mouse ovaries and short-interfering RNAs (siRNAs) were injected into the oocytes through the granulosa cell layers. After 6-day culture, oocyte survival rates and diameters of surviving oocytes were measured. The effect of siRNA was confirmed by RT-PCR from single oocytes and immunofluorescent staining with specific antibodies. Inhibition of ZP1, ZP2 and ZP3 synthesis by the corresponding siRNAs resulted in the impairment of oocyte growth and follicular development as well as ZP formation. Among the three ZP proteins, ZP3 showed the strongest inhibition in this experiment. These results suggested that all the ZP proteins and particularly ZP3 were associated with oocyte growth and follicular development in the ovary.