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

We have recently shown that a 90-kDa glycoprotein, acrin1 (MN7), is exclusi vely localized in the dorsal region of the acrosomal apical segment of matu re guinea pig sperm, and that its location changes during epididymal matura tion. The present study examined the process of transport and organization of this protein in the acrosome during spermatogenesis in the guinea pig te stis. Immunoperoxidase electron microscopy showed stage-specific localizati on of acrin1 within the developing acrosome, as follows: acrin1 first appea red in the proacrosomic vesicles of the early Golgi phase spermatids, and i t was then localized in the electron-lucent matrix region of the acrosomic vesicles of the late Golgi phase spermatids. During the cap phase, acrin1 w as abundant in the electron-lucent matrix of the acrosomal apical segment a nd in the head-cap region (principal segment). acrin1 became more restricte d 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, acrin 1 disappeared from the equatorial and principal segments, and it was finall y 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 proteolytic ally modified during epididymal sperm maturation. These results indicate th at acrosome morphogenesis is closely associated with the rearrangement of a crosomal proteins. Anat Rec 259:131-140, 2000. (C) 2000 Wiley-Liss, Inc.