Involvement of N-glycosylation of zona glycoproteins during meiotic maturation in sperm-zona pellucida interactions of porcine denuded oocytes.

The present study was conducted to delineate whether N-glycosylation of zona pellucida (ZP) glycoproteins occurred during meiotic maturation and whether this N-glycosylation played a role in sperm-ZP interactions of porcine cumulus denuded oocytes (DOs). After mechanical removal of cumulus cells from cumulus oocyte complexes (COCs), DOs were cultured for 44 h in in vitro maturation (IVM) culture. The experiments were carried out to determine the effects of tunicamycin, a specific N-glycosylation inhibitor, for various intervals during IVM on sperm-ZP interactions in porcine DOs. The results determined that DOs could induce meiotic maturation, although the maturation rate of DOs was earlier than that of COCs. In addition, N-glycosylation of ZP glycoproteins occurred during meiotic maturation and was crucial in sperm-ZP interactions, was responsible for sperm penetration, sperm binding to ZP and induction of acrosome reaction in ZP-bound sperm. However, the inhibition of N-glycosylation by tunicamycin during IVM did not influence ZP hardness and male pronuclear formation, indicating that this N-glycosylation was involved in the initial stage of fertilization. We conclude that 24-44 h of N-glycosylation of ZP glycoproteins during meiotic maturation was crucial in sperm penetration and sperm binding to ZP and the induction of acrosome reaction in sperm bound to ZP of porcine DOs.