Case Study on Role of Zona Pellucida Modifications during Meiotic Maturation in the Sperm-Egg Interactions of Poricne Oocytes

The oocyte maturation includes nuclear maturation and cytoplasmic maturation before fertilization. Moreover, the oocyte nucleus, the cytoplasm and other cell organelles occur changes, zona pellucida (ZP) synchronously undergoes biochemical and structural modifications in the final maturation phase of oocyte prior to fertilization (ZP maturation). It is reported that ZP modifications, such as glycosylation, sialylation, sulfation, glucosaminylation, fucosylation and galactosylation of glycoproteins, have been implicated in various events during fertilization. N-glycosylation of ZP glycoproteins during the meiotic maturation played a critical role in ZP acquiring the capacity to accept sperm in porcine cumulus oocyte complexes (COCs). In addition, the time course of sialylation is correlated with the induction of germinal vesicle breakdown (GVBD) during oocyte maturation. The sialylation of ZP glycoproteins during oocytes maturation is responsible for sperm-ZP interactions. Moreover, Sulfation in ZP glycoproteins during oocyte maturation is critically important in regulating the fundamental steps of sperm-ZP interactions. Although there is a correlation between the cumulus cells during meiotic maturation of porcine oocytes and N-glycosylation of ZP glycoproteins, the cumulus cells are not essential in sialylation and sulfation of ZP glycoproteins that responsible for sperm-ZP interactions.