Spergen-1 might be an adhesive molecule associated with mitochondria in the middle piece of spermatozoa

Spergen-1, a recently identified molecule specifically expressed in haploid spermatids in testis, is a small protein of 154 amino acids with a mitochondria-targeting signal at the N terminus. To examine the localization of spergen-1 protein in germ cells, we performed immunocytochemistry with the anti-spergen-1 antibody on frozen sections of rat testis and purified spermatozoa. Immunolabeling for spergen-1 was detected in mitochondria of elongating spermatids and of the middle pieces of matured spermatozoa. Immunoelectron microscopy revealed that spergen-1 was localized to the surface of mitochondria in the middle piece of spermatozoa. To investigate the properties of spergen-1, COS-7 cells were transfected with vectors encoding various spergen-1 mutants. The transfection experiments showed that spergen-1 expressed in the cells tended to agglutinate mitochondria and assemble them into aggregations and that the C-terminal region of spergen-1 as well as the N-terminal mitochondrial targeting signal was requisite for induction of mitochondrial aggregation. These results suggest that spergen-1, a mitochondria-associated molecule in spermatozoa, has a property to induce mitochondrial aggregation at least in cultured cells. We hypothesize that spergen-1 might function as an adhesive molecule to assemble mitochondria into the mitochondrial sheath around the outer dense fibers during spermiogenesis.     

Development of the acrosome and alignment,elongation and entrenchment of spermatids in procarbazine-treated rats

Intraperitoneally administered procarbazine caused, among other features previously reported (Russell et al., 1983), specific defects in the acrosome of cap phase spermatids of the rat seminiferous epithelium. The effect of procarbazine was to fragment and eventually cause resorption of the acrosomes of a small number of steps 5–9 spermatids. Although the acrosome was lost, dose union of the leaflets of the nuclear envelope underlying the acrosomal sac was maintained as was the marginal fossa and acrosomal zonule. Spermatids at steps 8 and 9 of development, which had lost their acrosomes, showed nuclei which were eccentric within the cell—a feature which normally occurs at these steps of spermiogenesis in acrosome intact cells. Even without an acrosomal sac, the plasma membrane of these cells (in stage VIII) became orientated to the region of the nuclear membrane which would have underlaid the acrosome. Although abundant, Sertoli ectoplasmic specialization did not become aligned with the spermatid head. The spermatid failed to become orientated within the seminiferous epithelium and failed to enter the crypts within the Sertoli cell as usually occurs during the elongation process. Thus, the presence of an acrosome is not likely related to the formation of an eccentric nucleus or the alignment of the surface of the nucleus which would normally underlay the acrosome with the cell's plasma membrane (internal alignment). The presence of an acrosome may be related to the alignment of the spermatid head with the ectoplasmic specialization, which in turn may influence the orientation and positioning of the late spermatids within the seminiferous epithelium (external alignment) and their position within recesses of the Sertoli cell. This study also suggests a role for the manchette in the process of elongation of the spermatid.     

Sperm development in the teleost Oryzias latipes

Summary In Oryzias latipes the processes of spermatogenesis and spermiogenesis occur within testicular or germinal cysts which are delimited by a single layer of lobule boundary cells. These cells, in addition to comprising the structural component of the cyst wall, ingest residual bodies cast off by developing spermatids. Therefore, they are deemed to be the homologue of mammalian Sertoli cells. The germ cells within a cyst develop synchronously owing to the presence of intercellular bridges connecting adjacent cells. Since bridges also connect spermatogonia, it seems probable that all of the germ cells within a cyst may form a single syncytium and do not exist as individual cells until the completion of spermiogenesis when the residual bodies are cast off. Significant differences between spermiogenesis in O. latipes and in the related poeciliid teleosts are discussed.     

Ultrastructural features of spermatozoa and their phylogenetic application in Zaprionus (Diptera,Drosophilidae)

The genus Zaprionus consists of approximately 60 species of drosophilids that are native to the Afrotropical region. The phylogenetic position of Zaprionus within the Drosophilidae family is still unresolved. In the present study, ultrastructural features of spermatozoa of 6 species of Zaprionus as well as the species Drosophila willistoni and Scaptodrosophila latifasciaeformis were analyzed. The ultrastructure revealed that the species have the same flagellar ultrastructure. Two mitochondrial derivatives, one larger than the other, close to the axoneme were present, primarily in D. willistoni (subgenus Sophophora). Except for Z. davidi and Z. tuberculatus, the analyzed species had paracrystalline material in both mitochondrial derivatives. Moreover, the testes showed 64 spermatozoa per bundle in all of the species. In the cluster analysis, 6 Zaprionus species were grouped closely, but there were some incongruent positions in the cladogram. The results indicated that sperm ultrastructure is an important tool for elucidating the phylogeny and taxonomy of insects.     

Fine structure of spermiogenesis with special reference to the spermatid morulae of the freshwater mussel Prisodon alatus (Bivalvia,Unionoidea)

Within the testicular cysts of the mussel Prisodon alatus are numerous somatic host cells described as Sertoli cells (SC), each containing a variable number of young spermatid morulae. Among them, several free spermatid morulae, spermatids, and spermatozoa were observed. Each free spermatid morula is surrounded by an external membrane. The early spermatids enclosed within the morulae have dense and homogeneous chromatin, and the cytoplasm occupies little space around the nucleus. Later, during spermiogenesis, the SC show lysis and disrupt to liberate the spermatid morulae. The membrane of the free morula is then disrupted, releasing the young spermatids. The SC disappear just after the appearance in the testis of a large number of free young spermatids. The nucleus of each free spermatid becomes gradually smaller and denser by the appearance of a granular pattern of condensed chromatin. During the maturation phase of the spermatids, the cytoplasm becomes more voluminous, and mitochondria and centrioles are more evident. Then, flagellogenesis occurs, and the nucleus gradually condenses into thicker strands. In the mature sperm, the apical zone has a disc-shaped acrosomal vesicle and the midpiece contains five mitochondria and two centrioles located at the same level. The flagellum has the common 9+2 microtubular pattern. The results are discussed with particular reference to Sertoli cells and clusters of spermatid morulae with those of species of closely related taxa in the bivalves. J. Morphol. 238:63–70, 1998. © 1998 Wiley-Liss, Inc.     

Fine structure of the germinating cells during the spermiogenesis of Arion rufus (Mollusca,Pulmonate Gastropoda)

Changes in spermatozoan ultrastructure have been studied during spermiogenesis of the slug Arion rufus (Gastropoda, Pulmonata, Stylommatophora). The ovotestis was investigated during the male stage, definite by the presence of spermatozoa. Some peculiar characteristics are shown by early spermatids: Around the nucleus, the nuclear envelope presents two thick layers located on opposite sides, the apical and basal plates, that will determine the antero-posterior axis of the spermatid. The chromatin, first dispersed throughout the nucleoplasm gives later on thick filaments which become attached over the inner surface of these plates. The chromatin filaments are then arranged parallel to the antero-posterior axis as the nucleus elongates. The position of the plates determines the antero-posterior axis of the spermatid. In the mature spermatozoa, the chromatin is more condensed and the nucleus presents an helical organization. The acrosome and flagellum are respectively attached externally to the center of the apical and basal plates. The acrosome consists of a membrane-bound vesicle and forms a column of homogeneous material. In the middle piece, the mitochondria have been transformed into a mitochondrial derivate by the way of a complicated metamorphosis. The axoneme is surrounded by three mitochondrial helices but only one of them contains glycogene granules. © 1996 Wiley-Liss, Inc.