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(52) FUNCTIONAL ASSAYS DEMONSTRATE THAT THE MOUSE ACROSOMAL PROTEIN SP-10 PLAYS A ROLE IN SPERM-ZONA BINDING. Herrero, Maria1, Digilio, Laura1, Monroe, Jennifer1, Herr, John1, Reddi, Prabhakara1, 1 University of Virginia, Charlottesville, VA ABSTRACT- Prior to fertilization, sperm undergo zona pellucida-induced acrosome reaction and release the acrosomal contents, which are believed to help the sperm traverse the zona matrix. Here we investigated the functional role of an evolutionarily conserved acrosomal matrix protein, SP-10, in sperm-egg interactions. Immunofluorescence data showed that all non-capacitated sperm contained SP-10 in the acrosome, whereas the majority of antibody staining was lost following acrosome reaction. We then asked whether SP-10 binds the zona pellucida or oolemma of mouse oocytes and if so, whether saturation of the binding sites at either location can prevent sperm binding/fusion. We found that the full-length mouse recombinant SP-10 protein bound to zona pellucida of intact oocytes and that this occupancy had a 65% inhibitory effect on sperm binding (p< 0.01). Further, incubation of sperm with an antibody specific to mouse SP-10 (purified IgG) had a similar inhibitory effect (73%, p< 0.01). In a parallel set of experiments we observed that incubation of zona-free oocytes with recombinant mSP-10 resulted in only a moderate inhibition of sperm-oolemma binding and had no effect on fusion. Incubation of sperm with anti mouse SP-10 IgG did not have an effect on binding or fusion. The contrasting results obtained with the zona-intact versus zona-free eggs suggest the possibility that the primary role of the SP-10 protein, which is released following the acrosome reaction, may be to facilitate sperm-zona binding. These results are in agreement with previous findings obtained in the bovine system. (HD29099, HD36239) KEY WORDS: ACROSOMAL PROTEIN, ZONA PELLUCIDA BINDING , MOUSE |
