Roles of mouse sperm-associated alpha-L-fucosidases in fertilization

Sperm-associated α-L-fucosidases have been implicated in fertilization in many species. Previously, we documented the existence of α-L-fucosidase in mouse cauda epididymal contents, and showed that sperm-associated α-L-fucosidase is cryptically stored within the acrosome and reappears within the sperm equatorial segment after the acrosome reaction. The enrichment of sperm membrane-associated α-L-fucosidase within the equatorial segment of acrosome-reacted cells implicates its roles during fertilization. Here, we document the absence of α-L-fucosidase in mouse oocytes and early embryos, and define roles of sperm associated α-L-fucosidase in fertilization using specific inhibitors and competitors. Mouse sperm were pretreated with deoxyfuconojirimycin (DFJ, an inhibitor of α-L-fucosidase) or with anti-fucosidase antibody; alternatively, mouse oocytes were pretreated with purified human liver α-L-fucosidase. Five-millimolar DFJ did not inhibit sperm-zona pellucida (ZP) binding, membrane binding, or fusion and penetration, but anti-fucosidase antibody and purified human liver α-L-fucosidase significantly decreased the frequency of these events. To evaluate sperm-associated α-L-fucosidase enzyme activity in post-fusion events, DFJ-pretreated sperm were microinjected into oocytes, and 2-pronuclear (2-PN) embryos were treated with 5 mM DFJ with no significant effects, suggesting that α-L-fucosidase enzyme activity does not play a role in post-fusion events and/or early embryo development in mice. The recognition and binding of mouse sperm to the ZP and oolemma involves the glycoprotein structure of α-L-fucosidase, but not its catalytic action. These observations suggest that deficits in fucosidase protein and/or the presence of anti-fucosidase antibody may be responsible for some types of infertility.