Spermatogenesis in the prosimian Galago Senegalensis : spermatogenic cycle timing, poly (A)+RNA localization, and spermiogenesis



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Spermatogenesis in the bush baby. Galago senegalensis, (Prosimi) was examined in cross sections of PAS-stained seminiferous tubules. Twelve stages with 15 distinct spermiogenic steps were identified in the spermatogenic cycle. The duration of the cycle as determined by 4 hr and 10 day 4 hr incorporation studies using tritiated thymidine, was 9.75days. The 15 spermiogenic steps were grouped into four phases, the Golgi phase (steps 1, 2), cap phase (steps 3-7), acrosome phase (steps 8-11), and maturation phase (steps 12-15), according to Clermont and Leblond's periodic acid Schiff-hematoxylin technique. The fine structure of representative spermatids of each step was examined and described. Nuclear condensation becomes pronounced late in step 7 and the acrosome becomes curved ventrally in steps 13-15. Distinctive 4 nm bundles of Sertoli cell microfilaments surrounded the head and neck region during steps 12-14, prior to spermiation which occurred at step 15. A prominent feature of step 14 and 15 spermatids is the membranous complex which is derived from the Golgi remnants, smooth endoplasmic reticulum, and other membranous elements of the residual cytoplasm. A microtubular complex was observed at the anterior limit of the principle piece of the tail as early as step 9. Except for the ventral curvature of the acrosome, and extreme development of a membrane complex in the neck region, the pattern and details of spermatogenesis closely resembled that described for higher primates. The temporal and spacial distribution of poly(A)+RNA during the spermatogenic cycle was analyzed by in situ hybridization of testes sections with (3H)-poly(U). The location of (3H)-poly(U):poly(A) complexes was detected by autoradiography at the light level and confirmed ultrastructurally. Alterations in the density and cellular distribution of grains were found to accompany the progressive differentiation of spermatids from the spermatogonia! cells in the seminiferous tubules. In spermatogonia, grain density is initially elevated in the nucleus (stages I-III), followed by a substantial increase in the cytoplasm (stages IV-VI). Later during spermatogonial development (stages VII-XII) nuclear and cytoplasmic grain density markedly decreased. In spermatocytes, although grain density above the nucleus becomes maximal during the leptotene-zygotene transition (stages VII-XI), no concommitant increase in cytoplasmic labeling was observed. The spermatids exhibited a progressive decrease in nuclear and cytoplasmic grain density (stages I-IX), until the pre- spermiation period (stages X-XII) when labeling was again elevated. Electron microscopic localization of poly(A)+RNA indicated a random distribution of grains in the nucleoplasm and cytoplasm. The data show three periods of poly(A)+RNA accumulation during the spermatogenic cycle; in the primary spermatogonial cells, during the leptotene-zygotene interphase in spermatocytes, and during the pre-spermiation period of spermatids. The first two periods correspond to intervals of intense DNA and RNA synthesis in other mammalian testes. The increased labeling in spermatids during the pre-spermiation period may indicate synthetic activity necessary for final spermatid maturation.