Transport and rearrangement of the intra-acrosomal protein acrin1 (MN7) during spermiogenesis in the guinea pig testis.

Abstract

We have recently shown that a 90-kDa glycoprotein, acrin1 (MN7), is exclusively localized in the dorsal region of the acrosomal apical segment of mature guinea pig sperm, and that its location changes during epididymal maturation. The present study examined the process of transport and organization of this protein in the acrosome during spermatogenesis in the guinea pig testis. Immunoperoxidase electron microscopy showed stage-specific localization of acrin1 within the developing acrosome, as follows: acrin1 first appeared in the proacrosomic vesicles of the early Golgi phase spermatids, and it was then localized in the electron-lucent matrix region of the acrosomic vesicles of the late Golgi phase spermatids. During the cap phase, acrin1 was abundant in the electron-lucent matrix of the acrosomal apical segment and in the head-cap region (principal segment). acrin1 became more restricted to the peripheral region of the electron-lucent matrix of acrosome phase spermatids and it was localized in the electron-lucent dorsal matrix region of maturation phase spermatids. In the final step of spermiogenesis, acrin1 disappeared from the equatorial and principal segments, and it was finally confined to the dorsal matrix region of the acrosomal apical segment. In addition, Western blot analysis showed that acrin1 of testes and epididymal sperm was of the identical size, indicating that acrin1 is not proteolytically modified during epididymal sperm maturation. These results indicate that acrosome morphogenesis is closely associated with the rearrangement of acrosomal proteins.