COMPARTMENTALIZATION, PROCESSING AND REDISTRIBUTION OF THE PLASMA-MEMBRANE PROTEIN CE9 ON RODENT SPERMATOZOA - RELATIONSHIP OF THE ANNULUS TO DOMAIN BOUNDARIES IN THE PLASMA-MEMBRANE OF THE TAIL

Western blotting, immunofluorescence and immunogold electron microscop y were used to examine the compartmentalization, processing and redist ribution of the integral plasma membrane protein CE9 on the spermatozo a of rats, mice and hamsters. In each species examined, spermatozoal C E9 was found to undergo endoproteolytic processing followed by a net r edistribution from the posterior-tail domain into the anterior-tail do main of the plasma membrane during epididymal maturation. Compared to spermatozoa of the rat and mouse, those of the hamster were found to e xpress a greater proportion of their CE9 within the anterior-tail plas ma membrane domain at all stages of maturation. As a consequence, CE9 was judged to be a suitable marker for two different spermatozoal plas ma membrane domains: the posterior-tail plasma membrane domain (sperma tozoa from the testis and caput epididymidis of the rat and mouse) and the anterior-tail domain (spermatozoa from the cauda epididymidis of the hamster). Immunogold electron microscopy was used to pinpoint the positions of the boundaries of these CE9-containing plasma membrane do mains at a high level of resolution. In each case, the position of the CE9 domain boundary was found to be strongly correlated with that of the subplasmalemmal electron-dense ring known as the annulus. The prec ise spatial relationship between the CE9 domain boundary and the annul us was, however, found to differ significantly among species and/or as a function of maturation.