Cytology of the human seminiferous epithelium

The appearances in cytologic specimens of the principal cell types in the normal human seminiferous epithelium are described and illustrated. Sertoli cells, which are larger than spermatogenic cells, are characterized by a slightly basophilic, ill-defined cytoplasm of triangular, elongated or columnar shape; the cytoplasm may be vacuolated and may contain spermatozoa. The nuclei of Sertoli cells are round, with a uniformly finely granulated chromatin and a single nucleolus. Spermatogenic cells are round or oval and show scanty cytoplasm with deeper basophilia and well-defined cytoplasmic borders. Multinucleation is common in spermatogenic cells. The Sertoli cells constitute a very homogeneous cell population as compared to the spermatogenic cells, which show several distinct cell types (spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoa) whose nuclear structures depend on the stage of meiosis. Both cell types may occur as naked nuclei. Some problems of cell classification are discussed.     

The lamina propria of the bovine seminiferous tubule

Summary The boundary tissue of bovine testicular seminiferous tubules exhibits remarkable regional differences at the level of the seminiferous tubule proper, as compared with its terminal segment. The basal lamina of the seminiferous tubule proper is multilayered and possesses knob-like protrusions. At the level of the terminal segment the basal lamina is highly specialized; in the region of the terminal plug candelabrum-like projections of the tubular basal lamina invade the bases of the modified supporting cells up to a depth of 3.5 m. The adjoining surface of these supporting cells is densely studded with hemidesmosomes. The elongated peritubular cells are arranged in 3–5 concentric layers around the tubulus seminiferus proper but form a loose association at the level of the terminal segment. Where the terminal segment joins the testicular straight tubule, peritubular cells may assemble to constitute a contractile spiral. Elastic tissue is situated mainly subjacent to the tubular basal lamina and to a lesser degree between the peritubular cell layers. A peritubular space lined by endothelium-like cells may surround the seminiferous tubule proper and also the transitional zone of the terminal segment.Supported by a grant from the Deutsche Forschungsgemeinschaft     

Organization and morphogenesis of the human seminiferous epithelium

Summary The various types of human primary spermatocytes were classified by means of morphological and morphometrical studies. Based on this classification, the topographic arrangement of the spermatocyte populations in the longitudinal course of seminiferous tubules was determined. This analysis revealed human spermatogenesis be to subjected to a complex local plan of organization, which is based upon the geometry of spirals.The centers of gravity of spermatocyte populations of subsequent degrees of differentiation are arranged on he lices that are contracted conically to the lumen of the seminiferous tubule. On these helices the centers of gravity of the populations diverge continuously 173.8°+/-32.4°. Populations of the same degrees of development are arranged on helices with constant diameters. On these helices the centers of gravity of the populations diverge continuously 142.6°+/-14.2°.The present results lead to new aspects of the kinetics and morphogenesis of the seminiferous epithelium, which can be integrated into a comprehensive biological concept.     

The cycle of the seminiferous epithelium in Landrace boars

The present study describes the morphological features of the eight stages of the seminiferous epithelium in Landrace boars according to the tubular morphology method, as well as their relative frequency, length, and duration. In Landrace boars the pre-meiotic stages occupied the 31.9 +/- 19.9% of the spermatogenic cycle and had a total length of 1788.8 +/- 1153.0 microm and a duration of 2.78 days; they were mainly characterised by the presence of leptotene and pachytene spermatocytes and round spermatids. Meiotic stages, with a relative frequency of 16.4 +/- 6.8%, a length of 787.1 +/- 603.1 microm and a duration of 1.41 days, contained spermatocytes in advanced meiosis I and/or in meiosis II and elongating spermatids grouped in bundles. Post-meiotic stages occupied the 50.6 +/- 20.4% of the spermatogenic cycle and had a length of 2096.8 +/- 1175.0 microm and a duration of 4.37 days; the most important event of these stages was the spermiation, which included the complete remodelling of sperm head and tail and the releasing of spermatozoa into the lumen, as well as the formation of residual bodies. From data obtained we concluded that both germ cell associations of the stages maintain constant among Landrace boars, and that the relative frequency, length and duration of the stages were directly dependent of the cytological transformations on the seminiferous tubules.     

hCG-induced maturation of the seminiferous epithelium in hypogonadotropic men

The effect of long-term hCG administration on sperm output was evaluated in a study in 3 hypogonadal patients with a selective deficiency of gonadotrophins (LH and FSH). The diagnosis of complete hypogonadotropic hypogonadism was based on clinical and hormonal findings as well as testicular histology. Pubertal maturation took place gradually during hCG therapy. 2 out 3 patients, who were azoospermic before treatment, had spermatozoa in their ejaculate after 12 and 24 months of therapy respectively. These effects on spermatogenesis were reversed after hCG withdrawal for 4 months and the patients again became azoospermic. This azoospermia was not reversed by testosterone (T) replacement therapy, or by addition of HMG to T. In vitro, the crude hCG preparation stimulated cAMP accumulation in rat Sertoli cell cultures indicating that this hCG preparation possesses an 'FSH-like' action. The present findings indicate that hCG therapy alone can induce and maintain spermatogenesis in some patients with complete hypogonadotropic hypogonadism.     

Short-time effects of taxol on the seminiferous epithelium of the rat

Summary The effect of taxol, an inhibitor of microtubule degradation, on the seminiferous epithelium was studied. Taxol arrested spermatogenesis at metaphase in both mitotic and meiotic germ cell division. Microtubules were seen to accumulate, especially in the cytoplasm of the spermatogonia, and also in the early spermatids and Sertoli cells. No microtubule accumulation was observed in germ cells during meiotic prophase. Formation of the flagellum was affected in developing spermatids. Peculiar lamellar structures, probably derived from degenerating mitochondria, were seen in the cytoplasm of late spermatids and Sertoli cells.The results are compared with the effects of other mitotic inhibitors such as colchicine and vinca alcaloids.     

Development of the seminiferous tubules after neonatal hemicastration in the boar

Development of the prepubertal seminiferous tubules of the right testis was characterized morphometrically every 14 days from 10 to 122 days of age in intact boars (I) and boars hemicastrated (HC) on Day 10 of life from two herds (Trial 1 and Trial 2). Comparisons were made between the remaining testis of Group HC boars and one testis in Group I boars. By 38 days of age seminiferous tubule length in Group HC boars was double (P less than 0.0001) that in Group I boars. Seminiferous tubule length did not differ between trials within treatments. The diameter of the seminiferous tubule was similar in Group HC and I boars but was greater (P less than 0.05) in Trial-1 than Trial-2 boars from Day 80 to 122 of life. Relative mass (mass of tissue/body mass) of Sertoli cells became 2-fold greater (P less than 0.0001), in Group HC than in one testis of Group I boars by 38 days of age and this difference was maintained throughout the experimental period. The relative mass of Sertoli cells was greater (P less than 0.05) in Trial-1 than Trial-2 boars within each treatment between 80 and 122 days of age. The relative mass of gonocytes was similar for all groups and treatments of boars. By 122 days of age the relative mass of spermatogenic cells was greater (P less than 0.05) in Group HC than in one testis of Group I boars and greater (P less than 0.01) in Trial-1 than Trial-2 boars within each treatment. Onset of spermatogenesis was first observed at 80 and 94 days of age in boars in Groups HC and I, respectively. Development of seminiferous tubule lumen was first observed at 94 and 108 days of age in boars in Groups HC and I respectively. Seminiferous tubule lumen, taken as a measure of fluid secretion of the Sertoli cells, occupied a greater (P less than 0.01) portion of seminiferous tubule in Trial-1 than Trial-2 boars within each treatment at the end of the experimental period. It is concluded that neonatal hemicastration of boars rapidly caused a compensatory seminiferous tubule elongation apparently due to Sertoli cell proliferation and an earlier onset of spermatogenesis. However, the gonocytes do not proliferate until they transform into spermatogonia.     

Cellular architecture of the lamina propria of human seminiferous tubules

Summary The lamina propria of human seminiferous tubules is composed of 5 to 7 cellular layers separated by laminae of extracellular connective-tissue components. By means of immunocytochemical methods the different nature of the cellular layers could be defined for the first time. Based on the light-microscopic demonstration of both desmin-like and vimentin-like immunoreactivity in the inner 3 to 4 layers of the lamina propria, these cells can be identified as myofibroblasts. The outermost one or two cellular layers, on the contrary, only show a vimentin-like immunoreactivity indicating the pure fibroblastic nature of these cells. Therefore, the outermost cellular layers are suggested to be derivatives of the interstitium. In cases of disturbed spermatogenesis, the lamina propria is frequently considerably thickened by an increase in the extracellular matrix components between the cellular layers. Whereas the ultrastructural localization of laminin-, collagen type-IV- and fibronectin-like immunoreactivity remains unaffected in the thickened lamina propria, the desmin-like immunoreactive cells of the inner layers strongly decrease in number and staining intensity. Most probably, the myofibro-blasts lose their myoid characteristics to participate in the secretion of increased amounts of extracellular matrix components, which in turn presumably block the mediation of the lamina propria between the interstitium and the germinal epithelium. It is still unclear whether the thickened lamina propria provokes the disturbance of spermatogenesis or vice versa.     

Vitamin C and oxidative stress in the seminiferous epithelium

In this article, we focus on the fundamental role of vitamin C transporters for the normal delivery of vitamin C to germ cells in the adluminal compartment of seminiferous tubules. We argue that the redox status within spermatozoa or in semen is partly responsible for the etiology of infertility. In this context, antioxidant defence plays a critical role in male fertility. Vitamin C, a micronutrient required for a wide variety of metabolic functions, has long been associated with male reproduction. Two systems for vitamin C transport have been described in mammals. Facilitative hexose transporters (GLUTs), with 14 known isoforms to date, GLUT1-GLUT14, transport the oxidized form of vitamin C (dehydroascorbic acid) into the cells. Sodium ascorbic acid co-transporters (SVCTs), SVCT1 and SVCT2 transport the reduced form of vitamin C (ascorbic acid). Sertoli cells control germ cell proliferation and differentiation through cell-cell communication and form the blood-testis barrier. Because the blood-testis barrier limits direct access of molecules from the plasma into the adluminal compartment of the seminiferous tubule, one important question is the method by which germ cells obtain vitamin C. Some interesting results have thrown light on this matter. Expression of SVCT2 and some isoforms of GLUT transporters in the testis have previously been described. Our group has demonstrated that Sertoli cells express functionally active vitamin C transporters. Kinetic characteristics were described for both transport systems (SVCT and GLUT systems). Sertoli cells are able to transport both forms of vitamin C. These findings are extremely relevant, because Sertoli cells may control the amount of vitamin C in the adluminal compartment, as well as regulating the availability of this metabolite throughout spermatogenesis.     

Fine structure of the transitional zone of the rat seminiferous tubule

An electron microscopic study was made on the structure of the testicular transitional zone (TZ) in the adult rat. The TZ proper consists of modified Sertoli cellss, with only a few spermatogonia and macrophages, surrounding distally a very narrow lumen. The TZ Sertoli cells have nuclei with a somewhat coarser matrix and more peripheral heterochromatin than Sertoli cell nuclei of the nearby seminiferous tubules, and the electron density of the cytoplasm varies from cell to cell. Smooth endoplasmic reticulum is abundant, but usually there are also scattered ribosomal rosettes and an occasional profile of rough endoplasmic reticulum. Microtubules are very numerous in the columnar portion of the cell, and laminar structures seemingly joining the cell surfaces are sometimes seen. Lipid droplets and lysosmal structures are frequent cellular components in proximal TZ Sertoli cells. Empty intracellular vacuoles are abundant, sometimes arranged around areas of smooth endoplasmic reticulum. Occasionally, membrane-limited fine granules and vacuoles are seen within Sertoli cells and also in the TZ lumen, suggesting a possible secretory activity by these cells. The apical processes of the Sertoli cells form large vacuolar structures, and in the basal parts of the epithelium vacuoles with capillary-like appearance are frequently seen. Phagocytosis of germinal cells by the Sertoli cells occurs in the proximal region of the TZ. Round waste bodies in contact with the Sertoli cell apices protruding into the tubulus rectus, are also common. The tunica propria of the TZ is thickened and somewhat wrinkled, and in the proximal region the myoid cell layer loses its continuity and is replaced by fibroblasts. The epithelium of the tubulus rectus adjacent to the TZ consists of several overlapping epithelial cells. The typical junctional complexes between TZ Sertoli cells appear to be impermeable to the lanthanum tracer.     

The cycle of the seminiferous epithelium in the Australian Swamp buffalo

The relative frequencies of stages and substages of the Swamp buffalo seminiferous epithelium were determined using a morphological classification. Duration of one cycle of the seminiferous epithelium was determined from radiolabelling studies using tritiated thymidine. Mean (+/-SD) duration of the cyle of the seminiferous epithelium of five Swamp buffalo was 8.74 +/- 0.18 d. Mean (+/-SEM) relative frequencies of stages and substages of the seminiferous epithelial cycle in ten bulls were Stage 1a, 7.27 +/- 0.72; Stage 1b, 8.11 +/- 0.85; Stage 1c, 8.54 +/- 1.13; Stage 2a, 5.9 +/- 0.79; Stage 2b, 7.49 +/- 0.78; Stage 3a, 9.05 +/- 0.66; Stage 3b, 9.69 +/- 1.11; Stage 4a, 5.04 +/- 0.44; Stage 4b, 4.8 +/- 0.69; Stage 5, 1.86 +/- 0.23; Stage 6, 8.81 +/- 0.84; Stage 7, 10.64 +/- 1.2; Stage 8a, 6.87 +/- 0.96; and Stage 8b, 5.93 +/- 0.72.     

Elastic tissue in the limiting membrane of the human seminiferous tubule

The structure and distribution of elastic tissue were studied in the limiting membrane of the seminiferous tubule from normal human testis. The elastic and elastic-related fibers (oxytalan and elaunin) were recognized by their tinctorial and ultrastructural characteristics. The connective structures of the limiting membrane, including the fibrotubules and the amorphous material of the elastic system, were studied after tannic acid-glutaraldehyde fixation. Fibrotubules (oxytalan fibers) were observed in almost all intercellular spaces of the limiting membrane, closely related to the contractile cells; the elaunin fibers (patches of amorphous material surrounded by bundles of fibrotubules) were evident in the outermost layers. The function of this system of elastic tissue and myoid cells is discussed, considering the permeability membrane and the role of the myoid cells in the elastogenesis and contractility of the seminiferous tubule.