BIOGENESIS OF THE POSTERIOR-TAIL PLASMA-MEMBRANE DOMAIN OF THE MAMMALIAN SPERMATOZOON - TARGETING AND LATERAL REDISTRIBUTION OF THE POSTERIOR-TAIL DOMAIN-SPECIFIC TRANSMEMBRANE PROTEIN CE9 DURING SPERMIOGENESIS

We used immunoperoxidase histochemistry and confocal immunofluorescenc e microscopy to examine the events involved in the compartmentalizatio n of CE9 to the posteriortail plasma membrane domain during spermatoge nesis in the rat. We identified two major episodes of spermatogenesis during which CE9 appeared to accumulate in relatively large amounts in tracellularly within elements of the secretory pathway. The first epis ode encompassed cells from preleptotene through early pachytene primar y spermatocytes and was evident as intense intracellular labeling of t he endoplasmic reticulum and the Golgi complex. The second episode enc ompassed spermatids in steps 8-12 of spermiogenesis and was evident as intense intracellular labeling of the Golgi complex and smaller vesic ular structures observed within the cytoplasm of the spermatid. Betwee n these two episodes, CE9 was detected in considerably reduced amounts . Although present within the Golgi complex and the acrosomic system t hroughout much of the first half of spermiogenesis, CE9 was not detect ed on the tail of the spermatid until steps 8-9 of spermiogenesis. Alt hough detected initially in relatively small amounts along the entire length of the tail beginning at steps 8-9, there was no evidence for t he presence of relatively large amounts of CE9 on the tail or anywhere else on the surface of the spermatid until after step 11 of spermioge nesis. Between step 11 and steps 13-14 of spermiogenesis, CE9 was obse rved to accumulate in relatively large amounts on the whole tail coinc ident with its apparent loss from the Golgi complex, CE9 was observed to then undergo further compartmentalization to the posterior-tail dom ain sometime between steps 13-14 of spermiogenesis and spermiation. Ou r results suggest that CE9 is synthesized and enters the secretory pat hway throughout much of spermatogenesis, but that the site of accumula tion of CE9 varies considerably as a function of development. With res pect to the biogenesis of the posterior-tail plasma membrane domain, o ur results suggest that CE9 is targeted from the Golgi complex to the plasma membrane of the whole tail during mid to late spermiogenesis an d then redistributes laterally into the posterior-tail domain coincide nt with the caudal migration of the annulus late in spermiogenesis. Th is proposed pathway has a number of important implications for the log istical capabilities of the mammalian spermatid. (C) 1995 Academic Pre ss, Inc.