Localization of actin in mammalian spermatozoa: a comparison of eight species

The distribution of monomeric and polymeric actin in spermatozoa from the bull, boar, rabbit, human, rat, mouse, golden hamster, and guinea pig has been examined by using a monoclonal antiactin antibody and NBD-phallacidin. Actin was present in sperm from each species. When the monoclonal antibody was used, there was a species-specific distribution and intensity of fluorescence, but no generalized pattern. Specific fluorescence was noted in the neck and principal piece of human sperm; in the postacrosomal region, neck, and midpiece of bull and boar sperm; in the postacrosomal region, neck, and principal/equatorial segment border of rabbit sperm; in the neck region of hamster sperm; and in the neck, midpiece, and principal piece of rat, mouse, and guinea pig sperm. Sperm from all eight species displayed no specific fluorescence with NBD-phallacidin, indicating that actin was present in a nonfilamentous form. SDS extracts of sperm were analyzed by SDS-PAGE and Western blotting; in sperm from each species, a 42-kD protein with specific affinity for the monoclonal antibody was present.