Localization of actin, alpha-actinin, and tropomyosin in bovine spermatozoa and epididymal epithelium.

Actin, alpha-actinin, and tropomyosin were localized in the testicular, epididymal, and ejaculated spermatozoa and in the epithelium of the bovine epididymis by means of specific antibodies using an indirect immunofluorescence technique. Immunocytochemical results were confirmed by the western blot analysis. Independent of the method of fixation, washing, or sonication, actin, alpha-actinin, and tropomyosin were all consistently localized in the neck of the spermatozoa. Actin and tropomyosin present in the postacrosomal area could be removed by sonication, whereas alpha-actinin in the basal plate appeared to be resistant to the treatment. In the unwashed spermatozoa alpha-actinin-specific immunofluorescence was seen over the acrosomal area, whereas in the washed sperm it appeared as a narrow cap at the margin of the head. In the latter location, its distribution was similar to that of tropomyosin. In the majority of preparations, tropomyosin could be localized in the principal piece of the tail. Even though some actin-specific immunofluorescence could be identified in the principal piece of the tail of the testicular and epididymal spermatozoa, a strong immunoreaction appeared only in the ejaculated spermatozoa. In the principal cells of the epididymal epithelium, specific fluorescence for actin, alpha-actinin, and tropomyosin occurred in the apical junctional complex. Basal bodies of the solitary cilia of the epididymal epithelium were labelled with antitropomyosin and anti-alpha-actinin antibodies. Besides offering new information about the cytoskeletal composition of the mammalian sperm, the present results support the hypothesized homology between the connecting piece of the sperm neck and the basal body of the cilia.