Intra‐acrosomally located acrosin‐inhibitors: Evolution and developmental patterns in mammals

Abstract

AbstractThe acrosome of the mammalian spermatozoon contains proacrosin that is autocatalytically activated to become the proteolytic enzyme acrosin during the process of fertilization. Tschesche et al [1982] isolated specific acrosin inhibitors and suggested that they block prematurely activated acrosin. Antibodies against acrosin inhibitors purified from boar spermatozoa were used to demonstrate the evolutionaary relationship and the developmental pattern of the inhibitors in mammals. Using immunofluorescent techniques the following results were obtained: (1) The spermatozoa of man, boar, bull, ram, rat, rabbit, beaver, and mole stained positive in the acrosomal portion. (2) The round‐headed spermatozoa of patients with globozoospermia and those in the ejaculates of fertile men lacked immunostaining for the inhibitors. (3) During spermatogenesis in all species, immunofluorescence for the acrosin inhibitors was first demonstrable in haploid spermatids and increased thereafter during spermatid differentiation. The stained area was found adjacent to the nuclear membrane, the position of the acrosome. (4) During teratogenesis of round‐headed spermatozoa, the immunofluorescent staining for the inhibitors becomes separated from the nuclear membrane of the spermatids and is lost in late spermatids. Since identical results have been described for acrosin and acrosomal membrane proteins both in spermatozoa and spermatids of mammalian species and during spermiogenesis of patients with globozoospermia, our results are consistent with the localisation of the inhibitors in the acrosome. Immunostaining of spermatozoa of species belonging to five different mammalian orders with the antibody against boar acrosin‐inhibitors is indicative of an evolutionary conservation of the inhibitors and their underlying genes.