Sperm from a variety of mammalian species express β1,4- galactosyltransferase on their surface

In mice, initial gamete recognition is mediated by the binding of sperm surface β1,4-galactosyltransferase (GalTase) to a glycoprotein of the zona pellucida, ZP3. When sperm bind to the zona pellucida, ZP3 induces the acrosome reaction by aggregating GalTase. The acrosome reaction releases acrosomal enzymes allowing sperm to pass through the zona pellucida, bind to the egg membrane, and activate development. In addition to GalTase, there is evidence that other sperm proteins may also bind ZP3. Although fertilization in the mouse is morphologically similar to fertilization in most other mammalian species, the degree of parallelism at the molecular level is not well defined. Less information is available about the molecular details of fertilization in other species. The aim of this work was to determine whether sperm from other mammalian species express GalTase on their surface. We performed GalTase enzyme assays on sperm from six species, and all six expressed GalTase on their surface. The amounts of GalTase varied between species. Guinea pig, moose, and rat sperm had higher levels of GalTase than bovine, porcine, and rabbit sperm. GalTase was localized by immunofluorescence on live and fixed sperm to the anterior portion of the sperm head in all species examined. This is the expected location for a receptor that binds the zona pellucida. Biotinylation of sperm surface proteins confirmed that GalTase detected by immunofluorescence and enzyme assay was expressed on the sperm surface. These results demonstrate that various mammalian species express GalTase on their surface and that it is found in the proper location to bind to the zona pellucida.