Continual maintenance of the blood-testis barrier during spermatogenesis: the intermediate compartment theory revisited

Tight junctions occur between the lateral processes of neighboring Sertoli cells that divide the seminiferous epithelium into two compartments: basal and adluminal compartments. These tight junctions constitute the blood-testis barrier (BTB). The established theory that the BTB must open when spermatocytes translocate from the basal compartment to the adluminal compartment is marked by one contradiction, that is, normal spermatogenesis occurs in the testis because the BTB is expected to constantly seclude the adluminal compartment from the basal compartment in order to protect haploid germ cells from the autoimmune system. Subsequently, another concept was proposed in which two BTBs divide the seminiferous epithelium into three compartments: basal, intermediate and adluminal compartments. It has been suggested that the transition from the basal region to the adluminal region without the BTB open occurs through the agency of a short-lived intermediate compartment embodying some primary spermatocytes. In contrast, the results of recent findings in the molecular architecture of the BTB suggest that the BTB in the seminiferous epithelium must "open". In this paper, I re-examine the BTBs of boar and experimental cryptorchid mouse testes by transmission electron microscope (TEM). TEM analysis showed that an atypical basal compartment existed in the thin seminiferous epithelium of 14-day post-cryptorchid mice testes. In developmental boar testes, ectoplasmic specialization (ES) of the seminiferous epithelium showed dynamic behavior. The intermediate compartment was clearly observed between the basal and adluminal compartments of the mature boar seminiferous epithelium. ESs were observed between Sertoli cells and spermatids at all developmental stages, including early, late and mature. Furthermore, ESs were situated on the apical surface of the seminiferous epithelium. From these results, I propose that the BTB is continually maintained during spermatogenesis and suggest a model of ES circulation in the seminiferous epithelium.     

Vitamin A Deprivation Affects the Progression of the Spermatogenic Wave and Initial Formation of the Blood-testis Barrier,Resulting in Irreversible Testicular Degeneration in Mice

The blood testis-barrier (BTB) is essential for maintaining homeostasis in the seminiferous epithelium. Although many studies have reported that vitamin A (VA) is required for the maintenance of spermatogenesis, the relationships between the BTB, spermatogenesis and VA have not been elucidated. In this study, we analyzed BTB assembly and spermatogenesis in the testes of mice fed the VA-deficient (VAD) diet from the prepubertal period to adulthood. During the prepubertal period, no changes were observed in the initiation and progression of the first spermatogenic wave in mice fed the VAD diet. However, the numbers of preleptotene/leptotene spermatocytes derived from the second spermatogenic wave onwards were decreased, and initial BTB formation was also delayed, as evidenced by the decreased expression of mRNAs encoding BTB components and VA signaling molecules. From 60 days postpartum, mice fed the VAD diet exhibited apoptosis of germ cells, arrest of meiosis, disruption of the BTB, and dramatically decreased testis size. Furthermore, vacuolization and calcification were observed in the seminiferous epithelium of adult mice fed the VAD diet. Re-initiation of spermatogenesis by VA replenishment in adult mice fed the VAD diet rescued BTB assembly after when the second spermatogenic wave initiated from the arrested spermatogonia reached the preleptotene/leptotene spermatocytes. These results suggested that BTB integrity was regulated by VA metabolism with meiotic progression and that the impermeable BTB was required for persistent spermatogenesis rather than meiotic initiation. In conclusion, consumption of the VAD diet led to critical defects in spermatogenesis progression and altered the dynamics of BTB assembly.     

Postnatal testicular development and actin appearance in the seminiferous epithelium of the Habu,Trimeresurus flavoviridis

The postnatal testicular development and actin distribution in the seminiferous epithelium were examined by light microscopy, using the testes of the Habu (Trimeresurus flavoviridis; snake) from 0-year-old to 3-year-old. At 0-year-old (about 1 month after birth), the testis was quite small in size, and the seminiferous epithelium was composed of only Sertoli cells and large spermatogonia. Actin immunoreactivity was observed in the peritubular myoid cells, but could not be detected in the seminiferous epithelium. At 1-year-old (about 10 months after birth), the testicular size increased to a great degree. In the seminiferous epithelium, spermatocytes newly appeared. Actin could still not be detected in the seminiferous epithelium. At 2-year-old (about 1 year and 10 months after birth), the testes continued to develop in size. In the seminiferous epithelium, elongate spermatids and round spermatids were frequently seen, in addition to Sertoli cells, spermatogonia and spermatocytes. Thus, active spermatogenesis was clearly recognized at this age. Moreover, the actin distribution in the seminiferous epithelium was observed at the site between Sertoli cells and spermatids, as well as that at adult stage. The immunoreactivity of actin in the peritubular myoid cells gradually increased from 0-year-old to 2-year-old. Conclusively, it seems likely that spermatogenesis in the Habu initiates at 2-year-old, accompanying with the appearance of actin in the seminiferous epithelium.     

Expression of connexin 43 protein in testes, epididymides and prostates of stallions

REASONS FOR PERFORMING STUDY: Connexin 43 (Cx43) is a ubiquitously distributed gap junction protein in testes and other reproductive tissues. Adjacent cells share ions and small metabolites through intercellular channels, which are present in gap junctions. Previously, Cx43 has not been reported in testes, epididymides and prostates either in healthy stallions or cryptorchid horses. OBJECTIVES: To demonstrate the expression pattern of Cx43 in the reproductive tissues of stallions and examine whether naturally occurring bilateral cryptorchidism has any influence on distribution and expression of Cx43. METHODS: The expression and the presence of Cx43 protein were detected by means of immunohistochemistry and Western blot analysis using a polyclonal rabbit anti-Cx43 antibody. RESULTS: In stallions, gap junctions appeared as structures localised to cell-cell contacts between adjacent cells. In testes, Cx43 expression was detected in the interstitial tissue and seminiferous tubules, between Leydig and Sertoli, as well as Sertoli and germ cells. In epididymides, Cx43 was localised between epithelial cells, whereas in prostates, between secretory cells of the glandular epithelium. In the cryptorchid, a clear reduction of Cx43 signal was observed in all reproductive tissues. CONCLUSIONS: Coupling of Leydig cells via gap junctions may suggest that steroidogenic function of the testis is under the influence of these intercellular channels. Within seminiferous tubules, the expression was found to be stage-specific, pointing to its role in coordinating spermatogenesis. Differential distribution of Cx43 protein in the reproductive tract of normal and cryptorchid stallions indicates that expression is clearly dependent on the physiological status of the horse. POTENTIAL RELEVANCE: Detection of Cx43 expression in equine testicular, epididymal, and prostatic cells is important for a better understanding of the role of intercellular membrane channels in direct cell communication within the reproductive tract of stallions.     

Cell-cycle-dependent Colonization of Mouse Spermatogonial Stem Cells After Transplantation into Seminiferous Tubules

Spermatogonial stem cells (SSCs) migrate to the niche upon introduction into the seminiferous tubules of the testis of infertile animals. However, only 5–10% of the transplanted cells colonize recipient testes. In this study, we analyzed the impact of cell cycle on spermatogonial transplantation. We used fluorescent ubiquitination-based cell cycle indicator transgenic mice to examine the influence of cell cycle on SSC activity of mouse germline stem (GS) cells, a population of cultured spermatogonia enriched for SSCs. GS cells in the G1 phase are more efficient than those in the S/G2-M phase in colonizing the seminiferous tubules of adult mice. Cells in the G1 phase not only showed higher expression levels of GFRA1, a component of the GDNF self-renewal factor receptor, but also adhered more efficiently to laminin-coated plates. Furthermore, this cell cycle-dependency was not observed when cells were transplanted into immature pup recipients, which do not have the blood-testis barrier (BTB) between Sertoli cells, suggesting that cells in the G1 phase may passage through the BTB more readily than cells in the S/G2-M phase. Thus cell cycle status is an important factor in regulating SSC migration to the niche.     

Vimentin expression in testes of Arabian stallions

Reasons for performing study: Specific patterns of cytoskeletal filaments reflect a functional state of the cell. In testicular cells intermediate filaments (IFs) are of the vimentin type. Since it is known that Sertoli cells regulate the spermatogenic function in the male gonad, it became important to propose a system that could quantify the state of seminiferous tubular quality. To date, a Johnsen score system has never been used to equine testes. Objectives: To demonstrate the expression pattern of vimentin in testes of mature Arabian stallions and correlate its distribution with grade of seminiferous tubule impairment as indicated by a Johnsen score. Methods: For histological examination by the Johnsen method, routine haematoxylin‐eosin staining was used. Vimentin expression and its presence in testicular sections and testicular homogenates were detected by immunohistochemistry and western blot, respectively. Both analyses were performed qualitatively and quantitatively and further validated by ANOVA tests. Results: Distinct morphology of seminiferous tubules was found in testes harvested from 3 stallions. Vimentin in IFs was immunolocalised to the cytoplasm of Sertoli, Leydig and peritubular‐myoid cells. The intensity and pattern of the IFs staining was different in individual seminiferous tubules suggesting a correlation between vimentin expression and the severity of tubule degeneration. Qualitative results by immunohistochemistry and western blot were confirmed by further quantitative analyses. Conclusions: In equine testes, differential expression of vimentin was found to be correlated with the impairment of seminiferous tubules indicated by a decrease in Johnsen score. Potential relevance: The Johnsen score system may be a useful method to facilitate the identification of tubular alterations in the stallion testes. Combined histological and immunohistochemical approach may provide a detailed phenotypic classification of stallions with decreased fertility.     

Distribution of actin filaments in the seminiferous epithelium of the Habu,Trimeresurus flavoviridis

The distribution of actin filaments was examined in the seminiferous epithelium of the Habu (Trimeresurus flavoviridis; snake), by transmission electron microscopy and fluorescence histochemistry. By transmission electron microscopy, actin filaments were clearly found only at the site between Sertoli cell and spermatid without a lattice‐like structure. Fluorescence histochemistry showed a weak labelling of actin filaments in the seminiferous epithelium, whereas these findings seem to be common among reptiles, they are different from those in mammals. Additionally, the bundles of actin filaments adjacent to the plasma membrane of Sertoli cells, appeared in other reptiles, were not observed in the Habu.     

Seasonal Changes in the Immunolocalization of Cytoskeletal Proteins and Laminin in the Testis of the Black‐Backed Jackal (Canis mesomelas)

Manipulation of the reproductive activity of jackals is dependent on a thorough understanding of the reproductive biology of this species. This study describes seasonal morphological changes in the adult testis of the black‐backed jackal in relation to the immunoexpression of the basement membrane marker, laminin and the cytoskeletal proteins, cytokeratin, smooth muscle actin and vimentin. Laminin was immunolocalized in basement membranes surrounding seminiferous tubules, as well as in basement membranes associated with Leydig, peritubular myoid and vascular smooth muscle cells. Scalloped basement membranes enclosed seminiferous tubules in regressing testes. The seminiferous epithelium and interstitial tissue in all animals studied were cytokeratin immunonegative. Smooth muscle actin was demonstrated in vascular smooth muscle cells, as well as in peritubular myoid cells encircling seminiferous tubules. Vimentin immunoreactivity was exhibited in the cytoplasm of Sertoli cells, Leydig cells, vascular endothelial cells, vascular smooth muscle cells and fibrocytes. Vimentin immunostaining in Sertoli, Leydig and peritubular myoid cells varied depending on the functional state of the testis. The results of the study have shown that dramatic seasonal histological changes occur in the testes of the jackal. In addition, the use of immunohistochemistry accentuates these morphological changes.     

羊驼睾丸细胞凋亡及凋亡相关蛋白的定位

本研究旨在观察羊驼睾丸的出生后发育和精子发生过程中的细胞凋亡及凋亡相关蛋白Bcl2和Caspase3 的定位.取材新生、12月龄和24月龄羊驼的睾丸,用TUNEL法检测睾丸发育和精子发生过程的细胞凋亡,用免疫组织化学技术检测凋亡相关蛋白Bcl2和Caspase3在羊驼出生后发育和精子发生过程中的定位.结果显示在新生羊驼睾丸未检测到TUNEL阳性细胞,Caspase3和Bcl2表达于间质细胞,提示在新生期凋亡蛋白参与间质细胞凋亡的调节,为曲精小管的发育提供空间;12月龄羊驼睾丸TUNEL阳性细胞定位于曲精小管中央部分,Caspase3 和Bcl2定位于间质细胞和曲精小管中央生殖细胞,提示在青春期(12月龄)羊驼睾丸,细胞凋亡和凋亡相关蛋白参与曲精小管管腔形成的调节;24月龄羊驼睾丸TUNEL阳性细胞定位于精原细胞、精母细胞和精子细胞,Caspase3 和Bcl2定位于间质细胞和各个发育阶段的生精细胞,Caspase3阳性细胞在精原细胞最高,向精母细胞和精子细胞逐渐减少,Bcl2在精原细胞弱阳性表达,在血睾屏障以内的曲精小管近腔室部分呈弥散性强阳性表达,提示在性成熟(24月龄)羊驼睾丸精子发生过程中,细胞凋亡主要发生于精原细胞和早期精母细胞,Bcl2可能抑制精母细胞之后生殖细胞的凋亡.结果提示在羊驼睾丸出生后发育和精子发生过程中存在细胞凋亡现象;凋亡蛋白Caspase3和Bcl2参与羊驼睾丸发育和精子发生过程中细胞凋亡的调节.     

Changes in the tubular compartment of the testis of Gallus domesticus during development

1.?The aim of the present study was to analyze histological and stereological changes in the tubular compartment in Gallus domesticus testes, as well as the variations in the number and size of their cells, from the start of morphological differentiation of the gonads (8-d chick-embryo) until the adult reproductive stage (28 weeks old).

2.?In embryonic chick testes, the total volume occupied by the interstitial tissue is greater than that occupied by the tubular compartment, but in the post-hatched chick the total volume of tubular compartment exceeds that of the interstitial tissue.

3.?From day 1 until 28 weeks of age, the seminiferous tubules increased in total volume, diameter, and epithelial height, which was directly related to the increase in the number of Sertoli and germ cells and the size of Sertoli cells.

4.?In the testes of one-day- and 6-week-old chicks, Sertoli cells were the most abundant cell type in the seminiferous tubules due to hyperplasia, but in 28-week-old birds the germ cells were the most abundant cell type. Hypertrophy rather than hyperplasia of Sertoli cells appears to be responsible for the increase in the total volume of seminiferous tubules.

5.?There are marked age-dependent changes in the tubular compartment of chick testes that help to understand the histological and stereological events occurring during normal development.     

Testicular degeneration and necrosis induced by dietary cobalt

Dietary cobalt (265 ppm Co) induced polycythemia and consistent degenerative and necrotic lesions in the seminiferous tubules of rats. Cyanosis and engorgement of testicular vasculature on day 35 and thereafter was followed on day 70 by degenerative and necrotic changes in the germinal epithelium and Sertoli cells. Spermatogonia, primary spermatocytes and round spermatids were markedly affected, while elongated spermatids, spermatozoa, and sertoli cells were more resistant. Damaged tubules, often present side by side with normal tubules, contained multinucleated giant cells composed of degenerated and necrotic spermatocytes and/or spermatids, sloughed germinal and Sertoli cells, and calcified necrotic debris. Necrotic tubules were frequently collapsed and devoid of epithelium except for occasional spermatogonia and surviving Sertoli cells. Lesions were not observed in the Leydig cells, cauda epididymis or seminal vesicles.     

Leydig cell hyperplasia in an ENU-induced mutant mouse with germ cell depletion

Repro22 is an N-ethyl-N-nitrosourea (ENU)-induced mutation in mice showing depletion of both male and female germ cells. In the present study, we investigated the male phenotypes of the mutant mouse at the adult stage. The repro22/repro22 homozygous mice showed reduced body weights as well as markedly reduced testis weights. Histological examination of the testes at 4 and 10 months of age showed no germ cells in the seminiferous tubules of the affected testis while a number of Sertoli cells were observed in the tubules. In addition to the germ cell depletion, the testes of the affected mouse contained expanded intertubular spaces that were filled by Leydig cell-like interstitial cells. These interstitial cells were confirmed to be Leydig cells by immunohistochmical staining using anti-3beta-HSD antibody. The estimated number of Leydig cells in the affected testes at 10 months of age increased approximately 2 fold compared with those of normal testes. Furthermore, the plasma testosterone levels of the affected mice at 10 months of age were significantly higher than those of the normal mice. These findings indicated that the repro22/repro22 mouse developed hyperplasia of Leydig cells that was presumably caused by the absence of germ cells in the seminiferous tubules.     

Expression of Connexin 43 in the Porcine Foetal Gonads During Development

This study was designed to reveal connexin 43 (Cx43) mRNA and protein expression in porcine foetal gonads using RT‐PCR, immunohistochemistry and Western blot analysis. Expression of Cx43 was investigated in porcine foetal ovaries and testes on days 50, 70 and 90 post coitum (p.c.). RT‐PCR results indicated that Cx43 mRNA was expressed in both foetal ovaries and testes at all gestational ages examined. Cx43 protein was found in the foetal ovary but its distribution varied across ovarian compartments and changed during development. In foetal ovaries, Cx43 was localized between the interstitial cells surrounding egg nests on all investigated days of prenatal period. Moreover, Cx43 expression was observed between germ cells on day 50 p.c. as well as between pre‐granulosa and granulosa cells of primordial and primary follicles on days 70 and 90 p.c. In the foetal testes, Cx43 protein was detected between neighbouring Leydig cells on all examined days of prenatal period and between adjacent Sertoli cells exclusively on day 90 p.c. The presence of Cx43 protein in all investigated foetal gonads was confirmed by Western blot analysis. Cx43 protein detection between pre‐granulosa cells of primordial follicles suggests its role in regulation of the initial stages of follicle development. The Cx43 immunoexpression between neighbouring Leydig and between Sertoli cells indicates its involvement in controlling their functions. We propose that Cx43‐mediated gap junctional communication is involved in the regulation of porcine foetal gonadal development.     

Reduced mitotic activity and increased apoptosis of fetal sertoli cells in rat hypogonadic (hgn/hgn) testes

Sterility in male hypogonadic (hgn/hgn) rats results from congenital testicular dysplasia caused by a single recessive gene hgn on rat chromosome 10. We recently identified an insertion mutation in the Spag5/astrin gene of hgn/hgn rats that may cause defective proliferation of immature Sertoli cells in the postnatal hgn/hgn testis. Since the pathological alterations were present in the testes at birth, we examined the involvement of defective mitosis and apoptotic cell death in embryonic development of hgn/hgn testes. Testicular hypoplasia was apparent at embryonic day (ED) 18.5. Immunostaining of hgn/hgn testes at ED 21.5 with antibody to GATA-4, which is specific for fetal Sertoli cells in the seminiferous cords, showed that the significant decrease in the number of fetal Sertoli cells was accompanied by a two fold increase in their mitotic index and abnormal mitosis and apoptosis. Prior to this, we observed a decrease in the number of BrdU-labeled cells, an increase in the number of TUNEL-positive apoptotic cells, and presence of MIS-positive apoptotic cells in hgn/hgn testes on ED 17.5 and 18.5. These results suggest that the Spag5 mutation may cause a reduction in mitotic activity and an increase in apoptosis of fetal Sertoli cells in hgn/hgn testes.     

The Expression of Epidermal Growth Factor (EGF) and its Receptor (EGFR) During Post‐Natal Testes Development in the Yak

Growth factors play critical role in cell proliferation, regulate tissue differentiation and modulate organogenesis. Several growth factors have been identified in the testes of various mammalian species in last few years. In present investigation, the objective was to determine the expression of epidermal growth factor (EGF) and the epidermal growth factor receptor (EGFR) in yak testicular tissue by relative quantitative real time polymerase chain reaction (RT‐PCR), Western blot (WB) and immunohistochemistry (IHC) from mRNA and protein levels. The testicular tissues were collected from male yak at 6 and 24 months old. Results of RT‐PCR and WB showed that the expression quantity of EGF and EGFR at 24 months of age was higher than at 6 months, and the increase rate of EGFR on mRNA and protein levels was higher than the increase rate EGF during post‐natal testes development. Positive staining for EGF and EGFR was very low and mainly localized to Leydig cells testes at 6 months of age with immunohistochemistry, and seminiferous tubules were not observed. At 24 month of age, both the EGF and EGFR could be detected in Leydig cells, peritubular myoid cells, sertoli cells and germ cells of the yak testes. However, EGF and EGFR were localized to preferential adluminal compartment and basal compartment in the seminiferous tubules, respectively. In conclusion, the findings in present studies suggest that EGF and EGFR as important paracrine and/or autocrine regulators in yak testes development and spermatogenesis.     

Immunohistochemical study of osteopontin in boar testis

The expression of osteopontin (OPN) in boar testis was studied. Western blot analysis detected 66- and 32-kDa OPN immunopositive bands in the testes of adult boars. In postnatal piglets, the 66-kDa OPN band was detected in the testes, but not the 32-kDa band. In the newborn testis, OPN immunostaining was seen in gonocytes and in some supporting cells in the seminiferous tubules, as well as in interstitial Leydig cells. In the adult boar testis, OPN immunoreactivity was detected in seminiferous tubules with varying intensities. Intense OPN immunostaining was seen in the residual bodies and acrosomes in the spermatids while, occasionally, OPN immunostaining was seen in spermatogonia and various stage of spermatocytes but in few Sertoli cells in the seminiferous tubules. In addition, Leydig cells in adult boars were weakly immunostained with OPN. These findings suggest that OPN is detected in the majority of germ cells and is involved in spermatogenesis in boar testis.     

Effects of transport stress on pathological injury and main heat shock protein expression in the respiratory system of goats

The aim of the present study was to investigate the pathological injury and the expression of heat shock proteins in the caprine lung, trachea and bronchus under transport stress. 12 healthy male goats were selected and randomly divided into three groups. The control group (non-transported group), 2 hr transport-treated group and 6 hr transport-treated group. Morphological changes as well as the expression of heat shock proteins (HSPs, mainly HSP27, HSP70 and HSP90) in three parts of the respiratory tract were examined. Our results showed swollen mucosa and congestive blood vessels in mucous layer and submucosa, inflammatory cell infiltration as well as degeneration and necrosis of mucosal epithelial cells in trachea and bronchus of the transport-treated groups. The epithelial cells were degenerated, and the exfoliated cells and debris could be seen in the alveolar cavity. The results of immunohistochemistry showed that HSP27 and HSP70 were strongly expressed in tracheal and bronchial epithelium, glandular epithelium, vascular endothelium and bronchiole epithelium. And the amount of positive inflammatory cells was increased in transport-treated groups. Western blot results indicated that the expression of all three proteins had no obvious difference among the three groups in bronchi (p > .05). In trachea, there was no significant difference in the expression of heat shock proteins among the three groups except that the expression of HSP70 which was obviously higher in the two transported groups than the control group (p < .05). The expression level of HSP70 in the 2 hr transport-treated group was significantly higher than the 6 hr group (p < .05) and control groups (p < .05). However, there was no significant difference in the expression level of HSP27 and HSP90 in three groups (p > .05). In conclusion, our data showed that transport stress could damage the caprine respiratory system.     

Testicular superoxide dismutase activity, heat shock protein 70 concentration and blood plasma inhibin-alpha concentration of dogs with a Sertoli cell tumor in a unilateral cryptorchid testis

The proportions of Sertoli cell tumor (SCT), seminoma and Leydig cell tumor in 50 dogs with unilateral testicular tumors were 52%, 36% and 12%, respectively. The rate of occurrence of SCT in the cryptorchid testis was very high (71%). The testicular superoxide dismutase (SOD) activity, testicular heat shock protein (HSP) 70 concentration and peripheral blood plasma inhibin (INH)-alpha concentration of 10 dogs with a unilateral cryptorchid testis and no testicular tumors, 10 dogs with SCT in a unilateral cryptorchid testis and 10 normal dogs, all aged 5-15 years, were measured in order to identify high risk factors for the occurrence of SCT in the canine cryptorchid testis. The mean SOD activity in cryptorchid testes and SCTs was significantly lower and higher, respectively, than in normal testes (both P<0.01). The mean HSP 70 concentration in both cryptorchid testes and SCTs was significantly higher than in normal testes (both P<0.01). The mean plasma INH-alpha concentration of the cryptorchid and SCT dogs was significantly lower and higher, respectively, than in normal dogs (P<0.05 and 0.01, respectively). The low SOD activity in the cryptorchid testis, low blood plasma INH-alpha concentration of the cryptorchid dogs and high HSP 70 concentration in the SCTs may be related to the occurrence of SCT and tumor cell proliferation in canine cryptorchid testes.     

Testicular Structure and Seminal Pathway in the Yellowtail Tetra Astyanax altiparanae (Characiforms: Characidae)

This study aimed to describe testicular and its main ducts structure in the yellowtail tetra Astyanax altiparanae, contributing to the knowledge of the region in which semen is produced, storage and released, focusing mainly on the dynamic of germinal epithelium and Sertoli cells during germ cell maturation. Ten sexually mature male A. altiparanae had their testes processed according to the routine protocols to optical microscopy. Moreover, spermatic ducts and tubular compartment of the testes of three specimens were perfused with vinyl resin for gross anatomy and scanning electron microscopy. Astyanax altiparanae testes are paired organs, separated for most of their extension, joining posteriorly in a spermatic duct formed by a squamous simple epithelium. Seminiferous compartment presents anastomosing tubular type organisation, and spermatogonia spread along its extent. Spermatogenesis is of cystic type, and there is no main testicular duct. Spermatogenesis develops in ‘waves’, from posterior to anterior part of the gonad. Thus, while sperm is storage posteriorly, spermatogenesis keeps maturing germ cells anteriorly, making the germinal epithelium very dynamic, holding Sertoli cells that change their function as a cystic envelope to produce secretions of the seminal fluid and store sperm. Such kind of development is thought to be responsible by the high prolificacy of this species.