Identification of Actin in Boar Epididymal Spermatozoa

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Abstract
Nonmuscle actin has been identified in boar spermatozoa utilizing deoxyribonuclease (DNAse) and indirect immunofluorescence. The specificity of the labeling technique was verified by labeling of fibroblasts, by dependence on DNAse and by competition with muscle actin. Actin was localized in two places in boar spermatozoa: the postacrosomal region and the cytoplasmic droplet. The postacrosomal actin was not in filament bundles and did not meaningfully change location during transit from the testis to seminal plasma. Actin in the cytoplasmic droplet also was not in filament bundles nor could a contractile ring be identified in droplets pinching off cauda epididymal spermatozoa. Spermatids with caps and vestments of Sertoli cells labeled very brightly, indicating a role for actin in spermiogenesis. A role for sperm actin in capacitation and fertilization is discussed.