Expression of genes encoding zona pellucida glycoproteins and cortical granule distribution in porcine oocytes isolated from small and medium follicles in relation to puberty status of donors

Abstract

The zona pellucida proteins belong to a group of proteins that regulate the processes of gamete recognition, interaction, and fusion, since they are recognized as primary and secondary sperm receptors. It is suggested that cortical granule distribution is significantly associated with the zona pellucida structure and membrane preparation to cortical and acrosome reaction. Therefore, this study investigated the zona pellucida marker gene expression (ZP2 and ZP4 protein) in relation to cortical granules distribution in oocytes and puberty status of donors. Oocytes were collected from adult cyclic sows (isolated from medium and small follicles) and juvenile gilts (isolated only from small follicles). The oocytes were examined by RT-qPCR and by confocal microscopy. The expression of genes for ZP2 and ZP4 protein in oocytes collected from small follicles from cycling sows was higher in comparison to oocytes from medium follicles or oocytes collected from small follicles from juvenile gilts (P < 0.001). We also observed increased expression of both ZP2 and ZP4 mRNA in oocytes collected from small follicles (juvenile gilts) as compared to medium follicles (cycling sows) (P < 0.001). Moreover, we found a difference in the distribution of cortical granules. In oocytes from medium follicles, the peripheral localization of cortical granules was twice higher than their central concentration. However, in oocytes derived from small follicles (cyclic sows) cortical granules in comparison to oocytes from medium follicles were more centrally localized (P < 0.05). It has been suggested that the donor puberty status and the size of follicles significantly influenced the zona pellucida gene expression and cortical granule localization in porcine oocytes. This is accompanied by fertilization specificity and fertilizability of porcine oocytes in vitro.