Oviduct-specific glycoprotein modulates sperm-zona binding and improves efficiency of porcine fertilization in vitro

Oviduct-specific glycoprotein (OGP) displays estrus-associated regional and temporal differences in expression and localizes to the zona pellucida, perivitelline space, and plasma membrane of oviductal oocytes and embryos, suggesting that it may have a role in regulation of fertilization and/or early embryonic development. The aims of this study were to evaluate the effect of exogenous OGP on in vitro fertilization (IVF) and embryo development in the pig using a defined serum-free culture system. In vitro-matured porcine oocytes were incubated with homologous OGP (0, 1, 10, 20, and 40 mug/ml) for 3 h and then washed prior to IVF. Exposure of oocytes to 10 or 20 mug/ml porcine OGP (pOGP) significantly reduced the incidence of polyspermy compared with the control (P < 0.01) while maintaining high penetration rates. When oocytes, spermatozoa, or both were preincubated with 10 mug/ml pOGP prior to IVF, the incidence of polyspermy was similarly reduced (P < 0.01) by all three treatments without affecting penetration rates. The ability of spermatozoa to undergo calcium ionophore-induced acrosome reaction was similar with or without exposure to pOGP. However, significantly fewer spermatozoa (P < 0.01) bound to the zona pellucida when oocytes were preincubated with pOGP. To evaluate the effect of pOGP on embryo development, embryos were cultured in pOGP-supplemented medium for 48 h or 144 h. Both transient and continuous exposure to pOGP significantly enhanced cleavage and blastocyst formation rate compared with the control (P < 0.01). These data demonstrate that exposure of either in vitro-matured oocytes or spermatozoa to pOGP decreased polyspermy and spermatozoa binding while maintaining high penetration rates of pig oocytes fertilized in vitro. Furthermore, pOGP exerted an embryotrophic effect independent of effects demonstrated on spermatozoa and oocytes at fertilization.