SPERM FROM A VARIETY OF MAMMALIAN-SPECIES EXPRESS BETA-1,4-GALACTOSYLTRANSFERASE ON THEIR SURFACE

In mice, initial gamete recognition is mediated by the binding of sper m surface beta 1,4-galactosyltransferase (GalTase) to a glycoprotein o f the zona pellucida, ZP3. When sperm bind to the zona pellucida, ZP3 induces the acrosome reaction by aggregating GalTase. The acrosome rea ction releases acrosomal enzymes allowing sperm to pass through the zo na pellucida, bind to the egg membrane, and activate development. In a ddition to GalTase, there is evidence that other sperm proteins may al so bind ZP3. Although fertilization in the mouse is morphologically si milar to fertilization in most other mammalian species, the degree of parallelism at the molecular level is not well defined. Less informati on is available about the molecular details of fertilization in other species. The aim of this work was to determine whether sperm from othe r mammalian species express GalTase on their surface. We performed Gal Tase enzyme assays on sperm from six species, and all six expressed Ga lTase on their surface. The amounts of GalTase varied between species. Guinea pig, mouse, and rat sperm had higher levels of GalTase than bo vine, porcine, and rabbit sperm. GalTase was localized by immunofluore scence on live and fixed sperm to the anterior portion of the sperm he ad in all species examined. This is the expected location for a recept or that binds the zona pellucida. Biotinylation of sperm surface prote ins confirmed that GalTase detected by immunofluorescence and enzyme a ssay was expressed on the sperm surface. These results demonstrate tha t various mammalian species express GalTase on their surface and that it is found in the proper location to bind to the zona pellucida.