Distinct cytoskeletal domains revealed in sperm cells.

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Abstract
Antibodies against different cytoskeletal proteins were used to study the cytoskeletal organization of human spermatozoa. A positive staining with actin antiboies was seen in both the acrosomal cap region and the principal piece region of the tail. No staining was obtained with nitrobenzoxadiazol-phallacidin, suggesting that most of the actin was in the nonpolymerized form. Most of the myosin immunoreactivity was confined to a narrow band in the neck region of spermatozoa. Tubulin was located to the entire tail, whereas vimentin was only seen in a discrete band-like structure encircling the sperm head, apparently coinciding with the equatorial segment region. Surface staining of the spermatozoa with fluorochrome-coupled Helix pomatia agglutinin revealed a similar band-like structure that codistributed with the vimentin-specific staining. Instead, other lectin conjugates used labeled either the acrosomal cap region (peanut and soybean agglutinins), both the acrosomal cap and the postacrosomal region of the head (concanavalin A), or the whole sperm cell surface membrane (wheat germ and Lens culinaris agglutinins and Ricinus communis agglutinin I). In lectin blotting experiments, the H. pomatia agglutinin-binding was assigned to a 80,000-MW polypeptide which, together with vimentin, also resisted treatment with Triton X-100. Only the acrosomal cap and the principal piece of the tail were decorated with rabbit and hybridoma antibodies against an immunoanalog of erythrocyte .alpha.-spectrin (p230). p230 appeared to be the major calmodulin-binding polypeptide in spermatozoa, as shown by a direct overlay assay of electrophoretic blots of spermatozoa with 125I-calmodulin. Spermatozoa have a highly specialized cytoskeletal organization and the distribution of actin, spectrin and vimentin can be correlated with distinct surface specializations of the sperm cells. Cytoskeleton may regulate the maintenance of these surface assemblies and affect the spermatozoan function.