Based on inhibition tests, the alpha 6 beta 1 integrin was suggested to be a sperm receptor, but further experiments using gene deletion techniques have shown that neither oocyte (alpha 6, nor beta 1 integrin subunits were essential for mouse fertilization. Using Western blot analysis and immunofluorescence (flow cytometry and microscopy), we have shown that mouse sperm expresses the alpha 6 beta 1 integrin. As for oocytes, binding of GoH3 anti-alpha6 antibody to sperm induces specific inhibition of sperm fertilizing ability. Comparing zona-intact and zona-free eggs in fusion tests, we have shown that removal of the zona pellucida bypasses the alpha 6 beta 1 integrin role in the adhesion/fusion process of oocyte fertilization. The alpha 6 beta 1 integrin is expressed by both gametes and is functional during their membrane interactions. Our results, previous reports on fertilization of alpha 6 or beta 1 integrin subunit-deleted oocytes by wild-type sperm and the fusion ability of beta 1 mutant myoblasts when they were co-cultured with wild-type myoblasts suggest that the presence of alpha 6 beta 1 integrin on one of the two gamete membranes can rescue the fertilization process. This hypothesis is further supported by the recently reported exchange of membrane fragments occurring between gametes prior to fusion.
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