Reconstruction of a type-B configuration monkey Sertoli cell: size, shape, and configurational and specialized cell-to-cell relationships

A model of a stage-V monkey Sertoli cell was reconstructed from electron micrographs taken of semiserial sections. The configuration (type-B) was one in which spermatids were positioned near the lumen, their heads occupying shallow cylindrical recesses at the apical portion of the Sertoli cell. The cell volume was calculated to be 4,100 micron3, the surface area 2,400.68 micron2, and the surface-to-volume ratio 0.58:1. The reconstructed cell extended from the basal lamina to the tubular lumen and was generally of the tall columnar type although its surface contour was highly irregular. The dimensions of the cell [centripetal (68.46 micron), circumferential (18.40 micron), and longitudinal (21.63 micron)] were determined and cell surfaces designated. Relative and absolute surface areas of the reconstructed cell which faced other Sertoli cells, germ cells, basal lamina, and tubular lumen were calculated. Junctions and surface specializations were enumerated, catalogued, and depicted on diagrams of the cell surface. Where appropriate, type-A rat and type-B monkey Sertoli cells were compared and discussed. Morphometry was utilized to analyze the relative surface areas of germ cells adjoining the reconstructed cell to determine the percentage of their surface facing cellular and acellular elements, and these data were compared to data obtained for the rat.     

Spermatogenesis in goats with and without scrotum bipartition

The objective of the present research was to quantify the seminiferous epithelium cells, spermatogenesis efficiency and characterize the ultrastrucure of Sertoli cells in goats. Eighteen goats were used and divided into three groups: Group I - goats without bipartition of the scrotum; Group II - animals with bipartition of the scrotum in up to 50% of the testicular length; Group III - goats with bipartition of the scrotum in more than 50% of the testicular length. The goat testes in Group III had a greater number of primary spermatocytes (25.37 ± 4.55 cells per cross sections), spermatids (112 ± 15.12 cells per cross sections), and Sertoli cells (9.46 ± 1.74 cells per cross sections) than the animals in Groups I and II (P<0.05). The spermatogenic mitotic, meiotic, and general efficiency were greater in animals in Group III (1.25 ± 0.28; 5.12 ± 1.63; 6.44 ± 1.96) when compared to those in Groups I and II. Sheet-like processes originated from the Sertoli cell body as simple and smooth structures which involved almost all the surface of germ cells. Slender cord-like processes originated from Sertoli cells and also from the sheet-like processes. The relative frequency of the cycle stages showed differences among the groups of goats studied, and the highest frequency was in Stage 3 (20.68% for goats in Group I, 21.15% for those in Group II, and 16.89% for the animals in Group III). In conclusion, goats with bipartition of the scrotum have a greater number of germ and Sertoli cells per cross section of seminiferous tubule, that indicated a greater sperm production when compared to the other groups, and the ultrastructure of the Sertoli cell process did not present any relationship with bipartition of the scrotum.     

Effect of the microtubule disrupting agents,colchicine and vinblastine,on seminiferous tubule structure in the rat

Injections of colchicine or vinblastine were given intratesticularly and rats sacrificed 6 and 12 hr later. Colchicine and vinblastine produced identical morphological patterns of response in the seminiferous tubules resulting in arrest of germcell mitoses and meioses and a rapid depletion of the microtubules normally found within the Sertoli cell. Sloughing of cells into the lumen of seminiferous tubules was the most prominent feature noted. Germ cells and portions of the apical Sertoli cells were frequently sloughed together where they remained in close association. Usually germ cells and associated Sertoli cell fragments were cleaved from the wall of the seminiferous tubule at a level between dissimilar generations of germ cells, e.g. between spermatocytes and spermatids. This selective sloughing probably occurred as the result of the support normally provided by intercellular bridges which link clones of like germ cell types. Sequential steps in the process leading to sloughing of Sertoli-germ cell associations could be inferred from observations made in plastic 1 μm sections. Cell sloughing at 12 hr post-injection was generally more extensive. It was frequently noted that germ cells and the apical portions of Sertoli cells had been extruded to the level of the most adluminal tight junctions forming the blood-testis barrier. It was concluded that disruption of Sertoli microtubules was responsible for sloughing of Sertoli fragments and associated germ cells, and that the cytoskeletal support of the Sertoli cell was, at least in part, dependent upon the integrity of Sertoli microtubules. The Sertoli cell could not round-up after loss of its cytoskeletal support, due to the numerous attachment devices known to link it with various apically positioned germ cells. Thus, the cell was severed at some point along its delicate apical processes, as the consequence of forces produced by the ‘rounding-up’ process. Long-term sacrifice after vinblastine or colchicine treatment allowed the Sertoli cells to regain microtubules and long processes but not their typical configuration. Spermatogenesis remained severely impaired.     

beta-Nerve growth factor participates in an auto/paracrine pathway of regulation of the meiotic differentiation of rat spermatocytes

NGF appears to be involved in spermatogenesis. However, mice lacking NGF or TrkA genes do not survive more than a few days whereas p75(NTR) knockout mice are viable and fertile. Therefore, we addressed the effect of betaNGF on spermatogenesis by using the systems of rat germ cell culture we established previously. betaNGF did not modify the number of Sertoli cells, pachytene spermatocytes, secondary spermatocytes nor the half-life of round spermatids, but increased the number of secondary meiotic metaphases and decreased the number of round spermatids formed in vitro. These effects of betaNGF were reversible and maximal at about 4 x 10(-11) M. Conversely, K252a, a Trk-specific kinase inhibitor, enhanced the number of round spermatids above that of control cultures. The presence of betaNGF and its receptors TrkA and p75(NTR) was investigated in testis sections, in Sertoli cell and germ cell fractions, and in germ cell and Sertoli cell co-cultures. betaNGF was detected only in germ cells from pachytene spermatocytes of stages VII up to spermatids of stages IX-X. TrkA and p75(NTR) were detected in Sertoli cells and in these germ cells. Taken together, these results indicate that betaNGF should participate in an auto/paracrine pathway of regulation of the second meiotic division of rat spermatocytes in vivo.     

The microtubule plus end-binding protein EB1 is involved in Sertoli cell plasticity in testicular seminiferous tubules

Sertoli cells of testis belong to a unique type of polarized epithelial cells and are essential for spermatogenesis. They form the blood-testis barrier at the base of seminiferous tubule. Their numerous long, microtubule-rich processes extend inward and associate with developing germ cells to sustain germ cell growth and differentiation. How Sertoli cells develop and maintain their elaborate processes has been an intriguing question. Here we showed that, by microinjecting lentiviral preparations into mouse testes of 29 days postpartum, we were able to specifically label individual Sertoli cells with GFP, thus achieving a clear view of their natural configurations together with associated germ cells in situ. Moreover, compared to other microtubule plus end-tracking proteins such as CLIP-170 and p150(Glued), EB1 was highly expressed in Sertoli cells and located along microtubule bundles in Sertoli cell processes. Stable overexpression of a GFP-tagged dominant-negative EB1 mutant disrupted microtubule organizations in cultured Sertoli cells. Furthermore, its overexpression in testis Sertoli cells altered their shapes. Sertoli cells in situ became rod-like, with decreased basal and lateral cell processes. Seminiferous tubule circularity and germ cell number were also reduced. These data indicate a requirement of proper microtubule arrays for Sertoli cell plasticity and function in testis.     

Immunolocalization of cytochrome P450 aromatase in rat testis during postnatal development

Aromatization of androgens into estrogens in rat testis is catalyzed by the microsomal enzyme cytochrome P450 aromatase. In this work, aromatase cellular site was investigated in prepuberal, peripuberal and postpuberal testis, from 10-, 21- and 60-day-old rats respectively. Paraffin-embedded testis sections were processed for P450arom immunostaining using a rabbit polyclonal antiserum generated against purified human placental cytochrome P450 aromatase. Next, biotinylated anti-rabbit IgG was applied, followed by ABC/HRP/complex amplification with diaminobenzidine as chromogen. Prepuberal testis sections showed a strong immunoreactivity of aromatase in Sertoli cell cytoplasm while interstitial cells were immunonegative. In peripuberal testis sections, cytoplasmic immunoreaction was weak in Sertoli cells, but it was strong in spermatocytes and sporadic in Leydig cells. Postpuberal testis sections displayed a moderate aromatase immunoexpression in spermatocytes while a strong immunostaining was observed in round and elongated spermatids, as well as in Leydig cells. These results indicate a different age-dependence of aromatase localization in rat testicular cells during gonadal development. In particular, inside the seminiferous tubules, the aromatization site moves from Sertoli cells to late germ cells, suggesting a proliferative role of aromatase in prepuberal testis and its subsequent involvement in meiotic and post-meiotic germ cell maturation.     

Ameboid cells in spermatogenic cysts of caecilian testis

Sertoli cells constitute a permanent feature of the testis lobules in caecilians irrespective of the functional state of the testis. The developing germ cells are intimately associated with the Sertoli cells, which are adherent to the basal lamina, until spermiation. There are irregularly shaped cells in the cores of the testis lobules that interact with germ cells at the face opposite to their attachment with Sertoli cells. These irregularly shaped (ameboid) cells first appear in the lumen of the cysts containing primary spermatocytes and are continually present until spermiation. We did not observe any cytoplasmic continuity between a Sertoli cell and an ameboid cell. Both light microscopic and TEM observations reveal a phagocytic role for the ameboid cells: they scavenge the residual bodies shed by spermatozoa. Organization of the ameboid cells is grossly different from that of the spermatogenic and Sertoli cells. They appear to develop from the epithelium at the juncture of the collecting ductule with the testis lobule.     

Increased germ cell degeneration and reduced germ cell:Sertoli cell ratio in stallions with low sperm production

To determine the relationship between germ cell degeneration or germ cell:Sertoli cell ratio and daily sperm production, testes were obtained during the months of May to July (breeding season) and November to January (nonbreeding season) from adult (4 to 20-yr-old) stallions with either high (n = 15) or low (n = 15) sperm production. Serum was assayed for concentrations of LH, FSH and testosterone. Testes were assayed for testosterone content and for the number of elongated spermatids, after which parenchymal samples were prepared for histologic assessment. Using morphometric procedures, the types and numbers of spermatogonia, germ cells and Sertoli cells were determined. High sperm producing stallions had greater serum testosterone concentration, total intratesticular testosterone content, testicular parenchymal weight, seminiferous epithelial height, diameter of seminiferous tubules, numbers of A and B spermatogonia per testis, number of Sertoli cells per testis, and number of B spermatogonia, late primary spermatocytes, round spermatids and elongated spermatids per Sertoli cell than low sperm producing stallions (P < 0.05). The number of germ cells (total number of all spermatocytes and spermatids in Stage VIII tubules) accommodated by Sertoli cells was reduced in low sperm producing stallions (18.6 +/- 1.3 germ cells/Sertoli cell) compared with that of high sperm producing stallions (25.4 +/- 1.3 germ cells/Sertoli cell; P < 0.001). The conversion from (yield between) early to late primary spermatocytes and round to elongated spermatids was less efficient for the low sperm producing stallions (P < 0.05). Increased germ cell degeneration during early meiosis and spermiogenesis and reduced germ cell:Sertoli cell ratio was associated with low daily sperm production. These findings can be explained either by a compromised ability of the Sertoli cells to support germ cell division and/or maturation or the presence of defects in germ cells that predisposed them to degeneration.     

Stimulation of rat Sertoli cell secretory activity in vitro by germ cells and residual bodies

The direct influence of germ cells and residual bodies on Sertoli cell basal and FSH-stimulated secretion of androgen-binding protein (ABP) was studied using Sertoli cells, recovered from 20-day-old rats, cultured alone or cocultured with a crude germ cell preparation from adult rats or with pachytene spermatocytes, round spermatids or populations of residual bodies enriched by centrifugal elutriation. The effect of a rat liver epithelial cell line (LEC) on Sertoli cell function was also tested. Addition of a crude germ cell preparation increased basal and FSH-stimulated ABP secretion. Pachytene spermatocytes and residual bodies adhered to the Sertoli cell monolayer to a much greater extent than did round spermatids. Addition of pachytene spermatocytes markedly enhanced basal and FSH-stimulated ABP secretion over 12 days of culture. Round spermatids and residual bodies stimulated ABP secretion although to a lesser extent than did spermatocytes. Furthermore, the increase of FSH-stimulated ABP levels was not maintained after 4 or 8 days of culture. LEC also enhanced basal and FSH-induced ABP levels but the increase of FSH-induced ABP production was only observed until Day 8 of culture. The influence of LEC on Sertoli cell secretion could be mediated through the production of an extracellular matrix. It is concluded that germ cells, particularly pachytene spermatocytes, can directly stimulate Sertoli cell secretory activity in vitro.     

Morphometric studies on lipid inclusions in Sertoli cells during the spermatogenic cycle in the rat

Summary The volume and surface area of lipid inclusions often present in the cytoplasm of rat Sertoli cells was measured directly from semi-thin sections of perfusion-fixed testicular tissues using an image analyser linked to a light microscope. Sertoli cell nuclei were used as a reference for comparing any variations in the measured parameters of lipid inclusions during the rat spermatogenic cycle. Volume density of Sertoli cell lipid inclusions was assessed by morphometric analysis of Sertoli cells photographically reconstructed from electron micrographs. Maximum lipid content in Sertoli cells occurred during stages IX–XIV of the spermatogenic cycle, then declined at stages I–III and remained low from stages IV–VIII. The persistence and increase in number of many large Sertoli cell lipid inclusions beyond the stage where spermatid residual bodies are phagocytosed within the Sertoli cells (stage IX) suggests that the synthesis and lipolysis of Sertoli cell lipid inclusions represents an intrinsic functional cycle of the Sertoli cells. Stage-dependent variations in the lipid content of rat Sertoli cells offers morphological evidence that the metabolic duties of the Sertoli cells are synchronised with the spermatogenic cycle to provide local coordination of the proliferation and maturation of the germ cells.     

Concanavalin A-induced attachment of spermatogenic cells to Sertoli cells in vitro

Adhesive contacts between developing germ cells and Sertoli cells may play an important role in mammalian spermatogenesis. Adhesion between isolated spermatogenic cells (pachytene spermatocytes and round spermatids) and Sertoli cells was studied. The attachment of single mouse germ cells to mouse Sertoli cell layers was weak, but the rate of attachment was stimulated by Concanavalin A (conA; 5 μg/ml). ConA-induced attachment was largely stable during a subsequent incubation for 30 min in the presence of 20 mM α-methyl- -mannoside (an inhibitor of conA). The cellular specificity of the stable attachment of germ cells to Sertoli cells was inferred from the observations that a comparable inhibitor-resistant attachment could not be obtained between germ cells and kidney cells, and between mouse myeloma cells and Sertoli cells. Juxtaposition of male germ cells and Sertoli cells through conA bridges may lead to the subsequent formation of strong and specific cell-cell adhesive bonds.     

A novel perspective: the occluding zonule encircles the apex of the Sertoli cell as observed in birds

The modulation of Sertoli cell junctions was studied in the non-seasonal rooster (Gallus domesticus) and in the seasonally breeding mallard duck (Anas platyrynchos anatidae) using thin sectioning, a junction permeability tracer, and freeze-fracture replication. During the active spermatogenic phase, the junctions of the duck appeared similar to those of the rooster, thereby establishing the duck as an avian model of seasonal modulation of Sertoli cell junctions. As with mammalian seasonal breeders, during the active phase, occluding, gap, and adhering junctions formed a junctional complex all along the long axis of the Sertoli cell. Unlike in mammals, however, no 7-nm filaments were associated with the occluding junctions. An occluding zonule encircled the Sertoli cell apico-lateral membrane domain situated above the young germ cells, and constituted a barrier to the entry of lanthanum in the basal third of the seminiferous epithelium. Toward the basal side, forming focal junctions were located on the lateral Sertoli cell membrane domain facing the young germ cells. Toward the apical side, dismantling focal junctions were located on the apical Sertoli cell membrane domain facing the older germ cells. During the duck's testicular regression, 7-nm filaments were associated with an occluding junction. In freeze-fracture replicas, each junction was formed by a continuous junctional strand that encircled the apex of the cell. The strands composed a delicate narrow meshwork: an occluding zonule. The blood-testis barrier was localized near the apex of the epithelium. The seasonal reduction in the number of the strands and the changes in their orientation did not coincide with a change in the permeability of the occluding zonule to lanthanum. In addition, the cyclic disappearance of junction-associated filaments was not correlated with a change in the permeability of the junctions but with a change in the affinity of junctional particles for one or the other fracture face. It is proposed that the Sertoli cell plasma membrane domains situated apical and basal with respect to the occluding zonule be considered apical and lateral, respectively. The remaining domain facing the basement membrane would therefore be called basal. In the duck, the occluding zonule is not seasonally shifted from the base to the apex of the Sertoli cell. Instead, it remains stationed above the younger germ cells throughout the year.(ABSTRACT TRUNCATED AT 400 WORDS)     

Indirect Sertoli cell-mediated ablation of germ cells in mice expressing the inhibin-alpha promoter/herpes simplex virus thymidine kinase transgene

In the present study, we describe a novel mouse model for inducible germ cell ablation. The mice express herpes simplex virus thymidine kinase (HSV-TK) under the inhibin-alpha subunit promoter (Inhalpha). When adult transgenic (TG) mice were treated with famciclovir (FCV) for 4 wk, their spermatogenesis was totally abolished, with only Sertoli cells and few spermatids remaining in the seminiferous tubules. However, testicular steroidogenesis was not affected. Shorter treatment periods allowed us to follow up the progression of germ cell death: After 3 days, spermatogonia and preleptotene spermatocytes were no longer present. After a 1-wk treatment, spermatogonia, preleptotene, and zygotene spermatocytes were missing and the amount of pachytene spermatocytes was decreased. After a 2-wk treatment, round and elongating spermatids were present. During the third week, round spermatids were lost and, finally, after a 4-wk treatment, only Sertoli cells and few spermatids were present. Interestingly, the transgene is detected in Leydig and Sertoli cells but not in spermatogonia. This suggests that FCV is phosphorylated in Sertoli cells, and thereafter, leaks to neighboring spermatogonia, apparently through cell-cell junctions present, enabling trafficking of phosphorylated FCV. Because of the many mitotic divisions they pass through, the spermatogonia are very sensitive to toxins interfering with DNA replication, while nondividing Sertoli cells are protected. Using transillumination-assisted microdissection of the seminiferous tubules, the gene-expression patterns analyzed corresponded closely to the histologically observed progression of cell death. Thus, the model offers a new tool for studies on germ cell-Sertoli cell interactions by accurate alteration of the germ cell composition in seminiferous tubules.     

Ultrastructure of spermatogonia, spermatocytes, and sertoli cells in the testis of the crayfish, Procambarus paeninsulanus

The testes of the crayfish, Procambarus paeninsulanus, were prepared for light and transmission electron microscopy. During early stages of spermatogenesis, when the spermatogonia are dividing, processes from a single Sertoli cell extend between numerous spermatogonia. As the cells enter meiosis, many points of contact can be observed between the Sertoli cell processes and spermatocytes. These desmosome-gap junctions are maintained between the germ and Sertoli cells until the early spermatid stage.     

The numbers of Sertoli cells in mature Holstein bulls and their relationship to quantitative aspects of spermatogenesis

Testes from 37 Holstein bulls, 38-99 mo of age, were used to investigate the relationship of Sertoli cell number, Sertoli cell-germ cell ratios and other related factors to daily sperm production (DSP). DSP was assessed by enumeration of spermatids in testicular homogenates, whereas Sertoli cell and germ cell ratios were based on direct counts in 20 round Stage VIII seminiferous tubular cross sections per bull. Numbers of Sertoli cells were calculated as (total homogenization resistant spermatids:spermatid:Sertoli cell ratio)/0.394; the factor of 0.394 adjusted for the presence of homogenization resistant spermatids during only 39.4% of the spermatogenic cycle. Data were subjected to simple linear and second-order regression analyses. Positive linear relationships were observed between DSP and testicular parenchymal weight (p less than 0.005, R = +0.71), DSP per gram (p less than 0.005, R = +0.79), total Sertoli cells (p less than 0.005, R = +0.83), Sertoli cells per gram (p less than 0.01, R = +0.47) and the yield of Step 8 spermatids per Type A spermatogonium (p less than 0.05, R = +0.34). DSP was not related (p greater than 0.10) to the number of germ cells supported per Sertoli cell. Testicular parenchymal weight and DSP per gram were unrelated to each other (p greater than 0.10), but both were related (p less than 0.005) to the total Sertoli cell number (R = +0.61 and +0.62, respectively). Total number of Sertoli cells accounted for more of the variation in DSP between bulls (R2 = 68.2%) than did any other factor examined. It was suggested that total Sertoli cell number may be an important determinant of a bull's spermatogenic potential.     

Receptor-mediated endocytosis of testicular transferrin by germinal cells of the rat testis

Summary The present study examines events of the Sertoli cell iron delivery pathway following the secretion of diferric testicular transferrin (tTf) into the adluminal compartment of the rat seminiferous epithelium. The unidirectional secretion of tTf by Sertoli cells was verified, in vivo, and it was shown that this protein is internalized by adluminal germ cells. It was further determined by Scatchard analysis that this internalization was mediated by high affinity transferrin binding sites on the surface of round spermatids, numbering 1453/cell and displaying a K_d=0.6×10^-9 M. Northern blot analysis of RNA isolated from adluminal germ cells, namely spermatocytes, round spermatids and elongating spermatids, indicated that these cells expressed Tf receptor mRNA and ferritin mRNA in levels inversely related to their stage of maturation. Finally it was determined that following binding and internalization in round spermatids, Tf became associated with the endosomal compartment and was recycled back to the cell surface. This study illustrates the immediate fate of tTf once it is secreted by the Sertoli cell. Thus, diferric tTf binds of Tf receptor on the surface of adluminal germ cells, is internalized by receptor-mediated endocytosis and the apo Tf-Tf receptor complex is recycled back to the cell surface where apotTf is released into the adluminal fluid.     

Enzyme histochemical studies on the pathological changes in human Sertoli cells

Two forms of human Sertoli cell disorders were characterized enzyme histochemically from the testicular biopsy material of infertile and subfertile patients. Sertoli cell asthenia: a slight injury of the Sertoli cell with exfoliation of individual germ cells; marked by the rarefaction of reaction zones of thiamine pyrophosphatase (TPPase) and a decrease in lactate dehydrogenase (LDH). Sertoli cell insufficiency: severe Sertoli cell damage with the formation of a "puff" and a heavy exfoliation of germ cells (dislocation of Sertoli cell nucleus and cytoplasm along with the related germ cells into the lumen of seminiferous tubule); marked by a heterogeneous activity pattern of TPPase, the disappearance of LDH, maintenance of a slightly weakened activity of alkaline phosphatase, and an increase of acid phosphatase. In the case of Sertoli-cell-only syndrome, the high prismatic Sertoli cells showed strong acid phosphatase activity with scattered weak TPPase reaction, whereas the flat or cube-like Sertoli cells exhibited weak acid phosphatase activity with only one small round reaction zone of TPPase in each cell. In addition, the frequency of the occurrence of Sertoli cell asthenia, Sertoli cell insufficiency, and Sertoli-cell-only syndrome is reported, and its correlation with the andrological diseases discussed.     

Cytological and expression studies and quantitative analysis of the temporal and stage-specific effects of follicle-stimulating hormone and testosterone during cocultures of the normal human seminiferous epithelium

In vitro culturing of normal human seminiferous epithelium remains largely unexplored. To study normal human spermatogenesis in vitro, we used a micromethod for the purification and culture of Sertoli cells, spermatogonia A, spermatocytes, and early round spermatids. Cytological quantitative data for Sertoli and premeiotic germ cell cocultures isolated from normal testicular biopsies demonstrated that cells were able to proliferate (4%), complete meiosis (6.7%), and differentiate into late round (54%), elongating (49%), and elongated (17%) spermatids at similar in vivo time delays (up to 16 days) in response to FSH + testosterone stimulation. Cells maintained normal meiotic segregation, chromosome complements, and specific gene expression profiles. Follicle-stimulating hormone + testosterone stimulated spermatogonia proliferation and Sertoli cell survival. Follicle-stimulating hormone and especially FSH + testosterone increased diploid germ cell survival during the first week, whereas only FSH + testosterone was able to inhibit cell death during the second week of culture. Follicle-stimulating hormone and especially FSH + testosterone also stimulated meiosis resumption, although this was restricted to late pachytene and secondary spermatocytes. In contrast, spermiogenesis was only stimulated by FSH + testosterone. Expression studies showed that apoptosis was induced in the nucleus of diploid cells, and in nuclear and cytoplasmic compartments of spermatids, mainly triggered by the Fas pathway. Although junctional complexes between Sertoli and premeiotic germ cells were partially reacquired, the same did not apply to spermatids, suggesting that FSH potentiated by testosterone was unable to render Sertoli cells competent to bind round spermatids.     

Immunolocalization of inhibin and activin alpha and betaB subunits and expression of corresponding messenger RNAs in the human adult testis

Inhibin B is a testicular peptide hormone that regulates FSH secretion in a negative feedback loop. Inhibin B is a dimer of an alpha and a beta(B) subunit. In adult testes, the cellular site of production is still controversial, and it was hypothesized that germ cells contribute to inhibin B production. To determine which cell types in the testes may produce inhibin B, the immunohistochemical localization of the two subunits of inhibin B were examined in adult testicular biopsies with normal spermatogenesis, spermatogenic arrest, or Sertoli cell only (SCO) tubules. Moreover, using in situ hybridization with mRNA probes, the mRNA expression patterns of inhibin alpha and inhibin/activin beta(B) subunits have been investigated. In all testes, Sertoli cells and Leydig cells showed positive immunostaining for inhibin alpha subunit and expressed inhibin alpha subunit mRNA. Using inhibin beta(B) subunit immunoserum on testes with normal spermatogenesis and with spermatogenic arrest, intense labeling was located in germ cells from pachytene spermatocytes to round spermatids but not in Sertoli cells. Inhibin beta(B) subunit mRNA expression was intense in germ cells from spermatogonia to round spermatids and in Sertoli cells in these testes. In testes with SCO, high inhibin beta(B) subunit mRNA labeling density was observed in both Sertoli cells and Leydig cells, whereas beta(B) subunit immunostaining was negative for Sertoli cells and faintly positive for Leydig cells. These results agree with the recent opinion that inhibin B in adult men is possibly a joint product of Sertoli cells and germ cells.