A scanning electron microscopic study of germ cell maturation in the reproductive tract of the male soupfin shark (Galeorhinus galeus)

Germ cell maturation in the reproductive tract of the soupfin shark (Galeorhinus galeus) was studied using scanning electron microscopy (SEM). The SEM showed changes in Sertoli cytoplasm volume during spermatogenic development. In immature spermatocysts in the germinal zone, spermatogonia were embedded in Sertoli cytoplasm. In spermatogonial spermatocysts, Sertoli cells were adluminally located in the spermatocyst, with spermatogonia enveloped in the basal portions of the cytoplasm. During the round spermatid stage, Sertoli cytoplasm was very scanty. Spermatid elongation was accompanied by a progressive increase in the volume of Sertoli cytoplasm, notably around the spermatid heads. In the mature spermatocyst, bundles of spermatozoa are totally enveloped by Sertoli cytoplasm. Spermatozoa occurred randomly in the epididymis. However, in the ampulla ductus deferentis, spermatozoa reaggregated and were embedded in a mucoid substance to form highly ordered spherical bundles. In the sperm bundle, the spermatozoa heads were arranged such that the helical turns of adjacent spermatozoa were precisely aligned, and all the heads in the bundle formed a distinct apex. This study demonstrates the utility of exploring the relationship between germ cells and Sertoli cells in an evolutionarily ancient vertebrate, such as the shark.     

Sperm morphology in the black coral Cirrhipathes sp. (Anthozoa, Antipatharia)

Abstract. Male polyps of the antipatharian Cirrhipathes sp., collected along the coral reef of Siladen Island (Sulawesi, Indonesia), were studied in order to gain an insight into the reproductive biology. Spermatocysts (maximum size 120 μm) are located within the primary gametogenic mesenteries and are separated by mesenteric cell cytoplasmic extensions. Sperm, maturing along radial rows, have a fairly round shape and contain a series of electron-dense vesicles in the apical nuclear region. A single mitochondrion flanks the nucleus. A peculiar cup-like electron-dense body, edged with regularly spaced electron-dense granules, is interposed between the nucleus and the tail, and delimits a central region that includes two centrioles. Cross-sections of the cup-like body reveal that the distal centriole has a pericentriolar system, consisting of nine arms arranged in a radial pattern. Each arm branches into three processes that are connected to the electron-dense granules. Indirect evidence of spawning is derived from the accumulation of sperm in the gastric cavity. This process takes place through the lysis of the cells bordering the mesenteries. Intact cells of this bordering layer appear to be involved in the phagocytosis of non-expelled gametes.     

Testicular degeneration during spermatogenesis in the blue shark,Prionace glauca: Nonconformity with expression as seen in the diametric testes of other carcharhinids

The elasmobranch testis consists of spherical spermatocysts, each housing a single germ cell stage and its own clone of Sertoli cells. Because of the simple diametrical arrangement of cysts in maturational order, the testes of Squalus acanthias, Scyliorhinus canicula, and Prionace glauca are classified as the diametric shark testis type. The aim of this study was to document histologically the spermatocyst composition in the blue shark stage‐by‐stage and to establish whether the diametric testis type confers any uniformity regarding the expression of spermatogenesis in all sharks with this testis type. Analysis of the testes of blue sharks breeding in summer revealed extensive cyst degeneration of various forms and degrees, cyst shrinkage, and cyst disorganization with or without evidence of cell death, initially at the spermatogonia—spermatocyte transition but predominantly in spermatocyte and spermatid cysts. Animals could be grouped into two categories based on the major degenerative phenomena observed, namely those with extensive multinucleate cell (MNC) formation, and those with pronounced vacuolation in cysts. A major finding was the significant (P < 0.001) predominance of MNC formation and vacuolation in late‐stage spermatogonial cysts in the respective categories of sharks. Spermatocyte cysts showed varying degrees of germ cell depletion, with or without evidence of degeneration. Normal‐looking, but clearly subnormal‐sized primary and secondary spermatocyte cysts with no evidence of degeneration were significantly the dominant spermatocyte cyst types in both categories. It is proposed that these subnormal‐sized spermatocyte cysts could proceed into spermiogenesis. Because neighboring spermatid cysts lacked ordered bundling of spermatid heads (disorganized), a morphology significantly correlated with the vacuolation category of sharks, these results suggest that further progression into spermiogenesis was halted in such cysts. Thus, testicular degeneration in the diametric testis type is species specific in quantity and quality. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.