Features of impaired seminiferous tubule differentiation are associated with germ cell neoplasia in adult men surgically treated in childhood because of cryptorchidism

Seminiferous tubule differentiation was related to the occurrence of germ cell neoplasia in 38 men, aged 17-47, treated surgically in childhood for cryptorchidism. Tissues from 46 testes obtained from biopsies taken as a neoplastic preventive procedure or whole testes removed because of GCT were evaluated quantitatively. Paraffin sections were treated with antibodies against placental like alkaline phosphatase (PLAP), a marker of germ cell neoplasia, and cytokeratin 18 (CK-18), a marker of immature Sertoli cells. Quality of spermatogenesis and number Leydig cells were assessed with a score count. Seminiferous tubules diameter, thickness of basal membrane and size of intertubular spaces were measured with image analysis software. In 17.4% of testes spermatogenesis was normal (9.9 points) (N) and neoplasia was not found there. In the other 38 specimens (83%) spermatogenesis was abnormal (A). When spermatogenesis was arrested or when germ cells were absent (3.7+/-1.8 points), neoplastic lesions were found in 13.1% of the specimens. In A group 5.1+/-7.1% of tubules contained immature Sertoli cells, while in N they were not found. Tubular diameter was significantly lower in A (161.5+/-31.8 microm) than in N (184.6+/-24.3 microm) and the percentage of seminiferous tubules with the thickening of tubular basal membrane was also greater in A. Intertubular spaces were significantly larger in A (49.9+/-18.6%) in comparison to N group (32.6+/-12.5%). Mean number of Leydig cells was similar in both groups. To conclude, in most of the formerly cryptorchid testes, despite surgical treatment, impaired seminiferous tubules differentiation is predominant. Germ cell neoplasia is present in testes with retarded seminiferous tubules differentiation. Retardation of seminiferous tubule differentiation consists of inhibited spermatogenesis, presence of tubules with immature Sertoli cells, decreased tubular diameter, increased thickness of basal membrane and enlarged intertubular spaces. Examination of testicular biopsy with respect to the state of seminiferous tubule differentiation may be helpful to predict the appearance of germ cell neoplasia in adult men with cryptorchidism in anamnesis. Orchiopexy of cryptorchid testes may not prevent the occurrence of features of testicular dysgenesis and the associated germ cell neoplasia.     

Characterization of nuclear pore distribution in freeze-fracture replicas of seminiferous tubules isolated by transillumination.

Transilluminated seminiferous tubules were staged and utilized to determine the distribution of nuclear pore complexes in seminiferous tubules of the rat. Segments of seminiferous tubules of adult albino rats were separated and identified (in stages VII-VIII, IX-XI, XII-XIV, and V-VI), and then processed by freeze-fracture. Type A spermatogonia, the only spermatogonia located in seminiferous segments possessing stages IX-XI and XII-XIV, are oval cells in contact with the basal lamina. They either exhibit a random distribution of nuclear pores or a slight degree of clumping. Type B spermatogonia, found in segments possessing stages V-VI, exhibit, instead, a noticeable pore clustering. The identification of intermediate spermatogonia was not undertaken in this study. Preleptotene spermatocytes are easily identified in freeze-fracture by their location in segments with stages VII-VIII, by their arrangement in numerous groups between the basal lamina and the pachytene spermatocytes, and by their comparatively small size. They exhibit noticeable pore clustering. Leptotene (segments containing stages IX-XI) and zygotene (XII-XIV) spermatocytes show a more homogeneous distribution of nuclear pores. Pachytene spermatocytes are identified by their large size, by consistent detachment from the basal lamina and by being rather numerous and found in all the stages explored. Diplotene spermatocytes have the largest nuclei of all germ cells. They are always detached from the basal lamina and found only in seminiferous segments containing stage XIII. Pachytenes display a regular geometric array of pore aggregation with striking clustering, whereas diplotene nuclear pores takes on a random distribution. Secondary spermatocytes, only present in stage XIV intermingled with metaphase-anaphase profiles, are characterized in replicas by a paucity of evenly distributed nuclear pores.     

In situ demonstration of both TUNEL-labeled germ cell and Sertoli cell in the cimetidine-treated rats

Cimetidine has caused dysfunction in the male reproductive system. In the rat testis, intratubular alterations and loss of peritubular tissue due to peritubular myoid cell death by apoptosis have been recently shown. Thus, the aim of this study is to evaluate which cells of the seminiferous epithelium have been affected and/or died by apoptosis after the treatment with cimetidine. For this purpose, an experimental group containing five male albino Wistar rats received intraperitoneal injections of cimetidine (50 mg/kg body weight) during 52 days. The testes were fixed with 4% buffered formaldehyde and were embedded in paraffin. For detection of DNA breaks (apoptosis) in the cells of the seminiferous epithelium, the testicular sections were treated by the TUNEL method (Apop-Tag Plus Peroxidase Kit). In the tubules affected by cimetidine, altered peritubular tissue, including the presence of TUNEL labeling in the myoid peritubular cells, were usually found. In these tubules, the seminiferous epithelium exhibited low density of germ cells and TUNEL-positive labeling in the germ cells of the basal compartment. The concomitant staining in both germ cells of the basal compartment and late spermatids suggest a sensitivity of these cells in the damaged tubules. Besides germ cells, TUNEL-positive Sertoli cells were also found in the injured seminiferous tubules. Thus, a relationship between dying germ cells and Sertoli cell damage and/or death must be considered in tubules where peritubular tissue has been affected by toxicants.     

Immunohistochemical study of serum albumin in normal and cadmium-treated mouse testis organs by "in vivo cryotechnique"

The in vivo injection of cadmium (Cd) was reported to induce blood-testis barrier disruption, and assumed to be an experimental model to examine junctional structures in seminiferous tubules. The purpose of this study is to investigate time-dependent changes of albumin permeability in the normal or Cd-treated mouse testis by our "in vivo cryotechnique" with immunohistochemistry, reflecting tight junctional (TJ) barriers of Sertoli cells. The albumin in the seminiferous tubules was firstly immobilized by the cryotechnique, in which normal blood circulation was always kept. The cryofixed testicular tissues were then processed for freeze-substitution, and embedded in the paraffin wax. Serial sections were immunostained by anti-mouse albumin antibody with peroxidase immunostaining, and also stained with hematoxylin-eosine (HE) for morphological observation. In normal seminiferous tubules, the immunoreaction products were localized around peritubular myoid cells and between Leydig cells, as well as in blood vessels. They were also localized as arch-like patterns around some spermatogonia in basal compartments of seminiferous tubules. Twenty-four and 48 hrs after Cd-treatment, some enlarged spaces and vesicular formations in the seminiferous epithelium were observed on the HE-stained sections. The albumin immunolocalization was detected not only in the basal compartments, but also in the adluminal compartments between Sertoli cells and germ cells. Thus, the structural disruptions of inter-Sertoli TJ barriers could be clearly demonstrated by the "in vivo cryotechnique".     

Temporal germ cell development strategy during spermatogenesis within the testis of the Ground Skink, Scincella lateralis (Sauria: Scincidae)

Ground Skink (Scincella lateralis) testes were examined histologically to determine the testicular organization and germ cell development strategy employed during spermatogenesis. Testicular tissues were collected from 19 ground skinks from Aiken County, South Carolina during the months of March-June, August, and October. The testes consisted of seminiferous tubules lined with germinal epithelia in which germ cells matured in close association with Sertoli cells. As germ cells matured, they migrated away from the basal lamina of the epithelia towards the lumina of the seminiferous tubules. The testes were spermatogenically active during the months of March, April, May, June, and October (largest seminiferous tubule diameters and epithelial heights), but entered a quiescent period in August (smallest seminiferous tubule diameter and epithelial height) where only spermatogonia type A and B and early spermatocytes were present in low numbers within the seminiferous epithelium. Although the testicular organization was similar to other amniotes, a temporal germ cell development strategy was employed during spermatogenesis within Ground Skinks, similar to that of anamniotes. Thus, this skink's germ cell development strategy, which also has been recently reported in all other major reptilian clades, may represent an evolutionary intermediate in terms of testicular organization between anamniotes and birds and mammals.     

Influence of hormonal imbalance on the integrity of seminiferous epithelium in the testes of adult rats chronically exposed to letrozole and rats exposed to soya isoflavones during the prenatal period,lactation, and up to sexual maturity

The structural integrity of the germ cells in the seminiferous epithelium and the correct process of spermatogenesis are made possible by proteins that participate in the formation of different types of junctions. This study was performed on samples of the testes of 4 groups (2 experimental and 2 corresponding control) of male Wistar rats. In the first experimental group, the adult rats received letrozole – a nonsteroidal inhibitor of cytochrome P450 aromatase (P450arom). The second experimental group was exposed to soya isoflavones during the prenatal period, lactation, and up to sexual maturity. The aim of this study was to examine the immunoexpression of β-catenin, N-cadherin, occludin, connexin43, annexin V, and advanced glycation end products (AGE) in the seminiferous epithelium of rat testes with chronic estrogen deficiency and of rats exposed to soya isoflavones. Series of sections of the testes were stained using PAS and silver impregnation. Moreover, immunohistochemistry tests were performed. A semi-quantitative determination of protein immunoexpression was performed using Image J. The number of annexin V positive Sertoli cells per tubule were counted manually. Comparisons between the experimental and corresponding control groups were performed using a non-parametric Mann-Whitney U test. The most common alterations were prematurely sloughed germ cells in the lumen of the seminiferous tubules and invaginations of the seminiferous tubules. We observed a lower number of annexin V positive Sertoli cells and a lower expression of N-cadherin and occludin in the seminiferous epithelium of both groups of rats with hormonal imbalances. Moreover, a higher expression of AGE, a lower expression of connexin 43 and a lower amount of reticular fibers in the basal lamina of seminiferous tubules was present in rats treated with letrozole and a higher expression of β-catenin was found in rats exposed to soya isoflavones. The hormonal imbalance between androgens and estrogens resulted in a decreased number of annexin V positive Sertoli cells. This may be associated with a failed clearance of apoptotic germ cells that leads to disturbances in the blood-testis-barrier (BTB) by affecting the expression of junctional proteins in the seminiferous epithelium. Moreover, a decreased level of estrogens was also associated with an increased expression of AGEs and with a changed composition of basal lamina in the seminiferous tubules of rats. These changes could lead to germ cell sloughing and invaginations of the seminiferous tubules.     

Immunohistochemical study of a membrane skeletal molecule, protein 4.1G, in mouse seminiferous tubules

Protein 4.1 families have recently been established as potential organizers of an adherens system. In the adult mouse testis, protein 4.1G (4.1G) localized as a line pattern in both basal and adluminal compartments of the seminiferous tubules, attaching regions of germ cells and Sertoli cells. By double staining for 4.1G and F-actin, their localizations were shown to be different, indicating that 4.1G was localized in a region other than the basal and apical ectoplasmic specializations, which formed the Sertoli–Sertoli cell junction and Sertoli–spermatid junction, respectively. By electron microscopy, immunoreactive products were seen exclusively on the cell membranes of Sertoli cells, attaching to the various differentiating germ cells. The immunolocalization of cadherin was identical to that of 4.1G, supporting the idea that 4.1G may be functionally interconnected with adhesion molecules. In an experimental mouse model of cadmium treatment, in which tight and adherens junctions of seminiferous tubules were disrupted, the 4.1G immunostaining in the seminiferous tubules was dramatically decreased. These results indicate that 4.1G may have a basic adhesive function between Sertoli cells and germ cells from the side of Sertoli cells.     

Involution of seminiferous tubules in aged hamsters: an ultrastructural, immunohistochemical and quantitative morphological study

In this study, we examined the age-related changes on morphometric parameters and ultrastructure of seminiferous tubules, and on the expression of extracellular matrix proteins in lamina propria of Syrian hamsters. A significant decrease in the percentage of normal tubules and an increase in the percentage of hypospermatogenic and arrested maturation tubules was observed with aging. Aged animals showed a decrease in tubular diameter, tubular lumen, seminiferous epithelium volume and total tubular volume. However, the total length of seminiferous tubules was significantly increased with aging. The most important ultrastructural changes with aging were the thickening of the lamina propria, the presence of diverse abnormalities in the spermiogenesis process, degeneration of germ cells, and vacuolization and flattening of Sertoli cells showing abundant lipofucsin droplets and residual bodies. Laminin immunoreactivity was found along the lamina propria of seminiferous tubules both in young and aged animals. Fibronectin immunoreactivity was found along the lamina propria and blood vessels. Both laminin and fibronectin total volume of immunostaining per testis was increased in aged hamsters. In conclusion, the age-related changes in seminiferous tubules of hamster include: a decrease in tubular width and an increase in tubular length; widening of the lamina propria caused by a more extensive connective matrix between the peritubular cells and the basal membrane; and a strong disarrangement of the seminiferous epithelium, including germ cell degeneration and important alterations in both spermiogenesis and Sertoli cell structure.     

Intratesticular distribution of testosterone in rats and the relationship to the concentrations of a peptide that stimulates testosterone secretion

Methods have been established and validated for quantitative assessment of the distribution of testosterone in the testis, by measurement of testosterone concentrations in whole testis, in isolated seminiferous tubules and in testicular interstitial fluid. These measurements were made in individual rats injected 2-40 h previously with saline (0.9% NaCl) or a potent antiserum to ovine LH. Testosterone concentrations in interstitial fluid and seminiferous tubules were closely correlated (r = +0.98; n = 60) and their relationship was log linear over a 200-fold range. However, although the concentrations of testosterone in interstitial fluid and seminiferous tubules decreased progressively with time after LH antiserum injection, this decrease was far more pronounced for interstitial fluid. In association with this change there was a significant increase in the amounts of a locally-produced factor in interstitial fluid which stimulates basal and hCG-stimulated testosterone production by isolated purified Leydig cells. This increase was reversed by injection of hCG but not by peripheral injection of a dose (20 mg) of testosterone propionate which restored normal intratesticular concentrations of testosterone. It is concluded that the tubular 'conservation' of testosterone, which occurs as interstitial fluid levels of this steroid decrease, may be a consequence of restricted diffusion of testosterone out of the tubules, but is also associated with increased amounts of a peptide stimulator of testosterone production.     

Testicular histological examination of spermatogenetic activity in captive gorillas (Gorilla gorilla)

To clarify the reproductive state of male gorillas, we performed histological examinations on the testicles of 10 male gorillas (Gorilla gorilla). The testicular samples were obtained by autopsy, and ordinal histological preparations were made for light microscopy. The poor spermatogenesis of this species was characterized by the following findings: First, spermatogenesis was evident in only four samples. Meiosis progressed in two samples, but they lacked spermatogenesis. In the remaining four specimens, seminiferous tubules hyalinized without any sign of spermatogenesis. Second, seminiferous epithelia were thin even in the males in which spermatogenesis was observed. Third, degenerated seminiferous tubules were found in all specimens. Fourth, abnormally large syncytial cells were found in the tubules. Six stages in the epithelial cycle of the seminiferous tubules were identified. Testosterone staining made it clear that there were many Leydig cells with spherical or fusiform nuclei in an abundance of interstitial tissue. The relevance of the testicular architecture of gorillas to the mating system is discussed.     

大鼠睾丸间质组织内的生殖细胞

在本实验中,光镜和电镜观察发现,在一例正常大鼠的局部睾丸的间质组织中,存在着不同发育时期的生殖细胞,同时还见支持细胞。上述各类细胞的超微结构同精细管内的无明显差别;但在位置上,它们却是分散于间质组织内,或者同间质细胞紧密相靠排列,或者分布于血管周围。本事实表明,在大鼠睾丸的间质组织中,可能也存在着生殖细胞赖以生存、发育和分化的环境条件。本文对这一现象的意义作了讨论。     

Expression of polysialic acid, alpha- and beta-cantenins in adult toad testis in hibernation stage and after gonadotrophin--releasing hormone (GnRH) treatment

The Polysialic Acid (PSA), glycosydic moiety of the Neural Cell Adhesion Molecule (N-CAM), and alpha- and beta-Catenins, which mediate interaction between Cadherins and cytoskeletal proteins, participate in cell adhesion phenomena in numerous organs and tissues. We have performed an immunohistochemical analysis, in hibernating toad testis and in GnRH-reactivated hibernating animals. In hibernating toads we could demonstrate PSA-immunoreactivity (PSA-IR) within the seminiferous tubules, in clusters of primary spermatocytes, spermatids and spermatozoa, in follicular and Sertoli cells. PSA-IR was seen in peritubular, Leydig and efferent duct cells. In GnRH-treated toads PSA-IR persists in primary spermatocyte groups. alpha-Catenin is localized in the basal laminae of seminiferous tubules and in Leydig cells of hibernating toads. This did not change after hormonal treatment. In hibernating toads, beta-Catenin was detected only in Leydig cells and within seminiferous tubules on basal spermatocystes and limiting spermatozoa clusters. In GnRH-treated toads, the beta-Catenin-IR was less intense in Leydig cells and vanished within seminiferous tubules.     

The effect of cryptorchidism on the quantitative histology, histochemistry and hydrolytic enzyme activity of the rat testis.

Cryptorchidism of the mature rat testis led to degeneration of the seminiferous tubules and changes in enzyme patterns and activities. Spermatogenic stages 1-4, containing pachytene primary spermatocytes in late meiotic prophase, and stage 5, containing recently formed round spermatids, were damaged by 48 h. Within 96 h stages showed a loss of germinal cells into the lumen and this was almost complete by 192 h. Acid phosphatase showed increased histochemical activity in the basal area of the seminiferous tubule up to 96 h of cryptorchidism, and at 192 h much of the activity was located in large lipidcontaining bodies within the remaining seminiferous epithelium. Total and free biochemical acid phosphatase decreased during cryptorchidism in parallel with cell loss; there were no significant changes in total cathepsin D activity but free enzyme activity was increased throughout the experimental period indicating increased lability of lysosomes in the Sertoli cell. Lactate dehydrogenase activity was mainly tubular but succinate dehydrogenase also showed interstitial activity. Lipoamide dehydrogenase (NADH) was found mainly in the interstitium. During cryptorchidism both lactate and succinate dehydrogenase activity decreased in the tubules parallel to the loss of germinal cells, whereas lipoamide dehydrogenase (NADH) activity increased in both interstitial and tubular areas. It is suggested that the initial lesion in the seminiferous epithelium, produced by cryptorchidism is in the Sertoli cell and that germ cell damage may result from reduced function of the Sertoli cell.     

Observations on living rat spermatogenic cells in different developmental stages.

In the seminiferous tubules of the rat, as in most mammalian species, the developing germ cells form associations with constant cell composition. These cellular associations or stages follow each other in a regular manner along the seminiferous tubules giving rise to seminiferous epithelial wave. When a freshly isolated unstained seminiferous tubulus of the rat is subjected to transillumination under a stereomicroscope, the different segments of the seminiferous epithelial wave absorb light in a characteristic manner permitting their recognition. Using this technique, small segments with accurately known cell composition can be isolated and studied in living state with phase-contrast microscopy. In several cases, the phase-contrast microscopy gives more information about the cell morphology than conventional histological methods. In this study all major developmental steps from early spermatogonia to mature spermatids have been described. The findings of the present study can be used as reference material in the evaluation and identification of the various cell types of the seminiferous tubules obtained, e.g. by the Staput fractionation method. In addition, the findings may be helpful in the evaluation of spermatogenic and Sertoli cells in culture conditions.     

Testosterone micromilieu in staged rat seminiferous tubules

Endogenous testosterone concentrations in rat seminiferous tubules were measured in relation to different stages of the cycle of the seminiferous epithelium. For this purpose, the seminiferous tubules were mechanically separated from the interstitial tissue on a cooled (1 degree C) petri dish under a stereomicroscope without added medium. After recognition of the stages of the cycle by transillumination, the specimens were rapidly transferred by dry forceps into test tubes for testosterone radioimmunoassay. The results of the dry dissection method were compared with measurements on tubules that were kept after separation in phosphate buffered saline (PBS, pH 7.4), in order to reveal the possible leakage of testosterone from the tubules. The maximal concentration of testosterone per unit length of seminiferous tubule was found in stages VII and VIII of the cycle (288 +/- 60 fmol/cm, mean +/- SEM, n = 12), and the minimal in stages IX-XII (219 +/- 57 fmol/cm, P less than 0.01). If the levels were correlated with unit volumes of the seminiferous tubules, identical concentrations of testosterone (521-542 fmol/mm3, approx. 500 nmol/l) were found in the different stages of the cycle. Despite the similarity of testosterone concentrations in the different parts of the seminiferous tubules the local concentrations of biologically active (i.e. free) testosterone may be modulated by extracellular and intracellular androgen binding components.     

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     

Comparative ability of rat seminiferous tubules, interstitium, and whole testes to utilize cholesterol-1,5-3H as a substrate for testosterone synthesis and the intratesticular distribution of cholesterol side-chain cleavage enzyme.

Homogenates of rat seminiferous tubules, interstitium and intact testis tissues were assessed for their ability to convert cholesterol -1,2-3H to testosterone in vitro. While 3H-testosterone synthesis was observed in incubates of interstitial and whole testis homogenates, no synthesis was detectable in homogenates of seminiferous tubules. To determine whether cholesterol side-chain cleavage enzyme (CSCCE) was deficient or absent in tubules, mitochondria from tubules, interstitium and whole testes were analyzed for CSCCE activity by measuring conversion of cholesterol -26-14C to 14C-isocaproate (+pregnenolone). Interstitial mitochondrial preparations from each of six testes were found to be approximately 200 times more active in CSCCE than the corresponding tubule mitochondria, and 1600-1800 times more active on a specific activity basis. Although caution is required in extrapolation of in vitro data to the in vivo state, these findings suggest rat seminiferous tubules may be incapable of de novo testosterone biosynthesis and that this lack of synthetic ability may be due to a deficiency of CSCCE.     

Immunohistochemical study of protein 4.1B in the normal and W/W(v) mouse seminiferous epithelium.

Cell-cell adhesion is crucial not only for mechanical adhesion but also for tissue morphogenesis. Protein 4.1B, a member of the protein 4.1 family named from an erythrocyte membrane protein, is a potential organizer of an adherens system. In adult mouse seminiferous tubules, protein 4.1B localized in the basal compartment, especially in the attaching region of spermatogonia and Sertoli cells. Protein 4.1B localization and appearance were not different in each spermatogenic stage. Developmentally, protein 4.1B was not detected at postnatal day 3 (P3), was diffusely localized at P15, and was found in the basal compartment during the third week. By double staining for protein 4.1B and F-actin, their localizations were shown to be different, indicating that protein 4.1B was localized in a region lower than the basal ectoplasmic specialization that formed the Sertoli-Sertoli junction. By electron microscopy, immunoreactive products were seen mainly on the membranes of Sertoli cells. In the W/W(v) mutant mouse, the seminiferous epithelium had few germ cells. Protein 4.1B and beta-catenin were not detected, although the basal ectoplasmic specialization was retained. These results indicate that protein 4.1B may be related to the adhesion between Sertoli cells and germ cells, especially the spermatogonium.     

Postnatal development of the connexion between tubulus seminiferus and tubulus rectus in the bovine testis

Summary Histology and ultrastructure of the connexion of seminiferous and straight testicular tubules were studied in 58 bovine testes of 29 animals ranging from 4 to 52 weeks of postnatal development. In the 4th and 8th week seminiferous tubules are solid. Their non-germinal supporting cells possess spherical nuclei in a basal location and a great amount of granular endoplasmic reticulum. The straight tubules have a narrow lumen and a stratified epithelium rich in intercellular canaliculi. Between 20 and 25 weeks the seminiferous tubules acquire a lumen and develop a terminal segment, the tip of which (terminal plug) protrudes into the cup-shaped modification of the adjacent straight tubule. At 30 weeks the structural differentiation between seminiferous tubule proper and its terminal segment has proceeded: in the former spermatocytes and spermatids make their first appearance, and the supporting cells have transformed to Sertoli cells. In the latter the morphology of the supporting cell preserves a more primitive state. Starting from the 16th week and proceeding through the 30th week and further, the epithelium of the tubulus rectus close to the connexion with the seminiferous tubule becomes monolayered by rearrangement of its cells and advances along the basal lamina into the area of the seminiferous tubule. Those cells of the seminiferous tubule that are cut off from the basal lamina by invading rectus cells degenerate. Between 40 and 52 weeks the adult situation is principally achieved. The terminal segment of the seminiferous tubule is tripartite consisting of transitional region, intermediate portion, and terminal plug. The terminal segment is surrounded by a vascular plexus. The straight testicular tubule adjacent to the terminal segment is modified into a cup region encompassing the terminal plug, followed by a narrow stalk region, which is lined by simple columnar epithelium. Mononuclear free cells are a constant feature of the tubulus rectus epithelium in all stages of postnatal development.Supported by grant Wr 7/6-6 from the Deutsche Forschungsge-meinschaft