Testicular involution following optic enucleation

Summary The testes of adult male Syrian hamsters underwent involution within six weeks after optic enucleation. The diameter of the seminiferous tubules was 39% less than controls. Sertoli cells, spermatogonia, and primary spermatocytes were still present, but all steps of spermatids were completely absent from the involuted testes. Lipid droplets filled the Sertoli cell cytoplasm and often encroached upon the nucleus. Sertoli cells had sparse mitochondria and smooth endoplasmic reticulum, but Golgi cisternae were abundant. Typical SertoliSertoli junctions attached contiguous Sertoli cells. With lanthanum tracers it was demonstrated that these junctions were impenetrable; therefore, the bloodtestis barrier was deemed intact. Irregularly shaped protrusions often arose from the peritubular tissue and extended inward toward the seminiferous epithelium, often displacing the cytoplasm of the Sertoli cells and spermatogonia. The core of these protrusions consisted of irregular extensions of myoid cell cytoplasm surrounded by the myoid cells' basal lamina. External to the myoid cell basal lamina were bundles of collagen filaments with the basal lamina of the seminiferous epithelium forming the outermost layer of these protrusions. The apices of the Sertoli cells gave rise to numerous leaf-like processes that extended into and obliterated the lumen of the tubules. The Sertoli cell basal cytoplasm often contained phagocytized degenerating germ cells that appeared to give rise to the lipid droplets that filled the Sertoli cell cytoplasm. Acid phosphatase rich lysosome-like organelles were seen fusing with the degenerating germ cells and lipid droplets. The degenerating germ cells also were shown to contain acid phosphatase activity.     

Improvement of spermatogenesis in adult cryptorchid rat testis by intratesticular infusion of lactate.

In order to test the hypothesis that a lack of energy could be a cause of germ cell death at high temperatures, cryptorchid rats testes were infused with lactate, delivered by osmotic pumps over 3-15 days. In cryptorchid testes, the spermatids and spermatocytes were lost between 3 and 8 days. In cryptorchid testes supplemented with lactate, elongated spermatids persisted in a few seminiferous tubules at Day 15. Elimination of round spermatids occurred progressively between 3 and 15 days, mostly at stage VIII. The loss of spermatocytes increased after 8 days, and 30% of seminiferous tubules still contained meiotic or meiotic plus spermiogenetic cells at Day 15. After 8 days, the chromatin of step 8 round spermatids was abnormal and nuclear elongation did not commence. The Sertoli cell cytoplasm that was retracted toward the basal compartment of the seminiferous epithelium could not hold the germ cells of the adluminal compartment. Therefore, attachment of germ cells to Sertoli cells and the supply of lactate seem necessary for the development of germ cells at high temperatures. The improvement in spermatogenesis in cryptorchid supplemented testes for several days is a new finding.     

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.     

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.     

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.     

Factors affecting spermatogenesis in the stallion

Spermatogenesis is a process of division and differentiation by which spermatozoa are produced in seminiferous tubules. Seminiferous tubules are composed of somatic cells (myoid cells and Sertoli cells) and germ cells (spermatogonia, spermatocytes, and spermatids). Activities of these three germ cells divide spermatogenesis into spermatocytogenesis, meiosis, and spermiogenesis, respectively. Spermatocytogenesis involves mitotic cell division to increase the yield of spermatogenesis and to produce stem cells and primary spermatocytes. Meiosis involves duplication and exchange of genetic material and two cell divisions that reduce the chromosome number to haploid and yield four spermatids. Spermiogenesis is the differentiation without division of spherical spermatids into mature spermatids which are released from the luminal free surface as spermatozoa. The spermatogenic cycle (12.2 days in the horse) is superimposed on the three major divisions of spermatogenesis which takes 57 days. Spermatogenesis and germ cell degeneration can be quantified from numbers of germ cells in various steps of development throughout spermatogenesis, and quantitative measures are related to number of spermatozoa in the ejaculate. Germ cell degeneration occurs throughout spermatogenesis; however, the greatest seasonal impact on horses occurs during spermatocytogenesis. Daily spermatozoan production is related to the amount of germ cell degeneration, pubertal development, season of the year, and aging. Number of Sertoli cells and amount of smooth endoplasmic reticulum of Leydig cells and Leydig cell number are related to spermatozoan production. Seminiferous epithelium is sensitive to elevated temperature, dietary deficiencies, androgenic drugs (anabolic steroids), metals (cadmium and lead), x-ray exposure, dioxin, alcohol, and infectious diseases. However, these different factors may elicit the same temporary or permanent response in that degenerating germ cells become more common, multinucleate giant germ cells form by coalescence of spermatocytes or spermatids, the ratio of germ cells to Sertoli cells is reduced, and spermatozoan production is adversely affected. In short, spermatogenesis involves both mitotic and meiotic cell divisions and an unsurpassed example of cell differentiation in the production of the spermatozoon. Several extrinsic factors can influence spermatogenesis to cause a similar degenerative response of the seminiferous epithelium and reduce fertility of stallions.     

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.     

Taenia crassiceps: A secretion-substance of low molecular weight leads to disruption and apoptosis of seminiferous epithelium cells in male mice

The present research was performed to isolate and study the effects of a low molecular weight (<1300 Da) parasite-associated substance, obtained from peritoneal fluids of female mice infected with Taenia crassiceps cysticerci, on seminiferous epithelium cells of male mice testis. The results showed an intense disruption of Sertoli cells and germ cells within the seminiferous tubules of experimental mice, along with the destruction of their gap junction (GJ). Significant generalized apoptosis of germ cells within seminiferous tubules was determined by TUNEL staining (P = 0.0159). In addition, a significant number of infiltrating macrophages were found in the luminal space of these seminiferous tubules (P < 0.0001). Finally, electron microscopy studies revealed structural and morphological abnormalities in the somatic cells (Sertoli and Leydig cells) and in the germ cells, primarily in the round and elongate spermatids.     

Seasonal spermatogenic cycle and morphology of germ cells in the viviparous lizard Mabuya brachypoda (Squamata,Scincidae)

We describe seasonal variations of the histology of the seminiferous tubules and efferent ducts of the tropical, viviparous skink, Mabuya brachypoda, throughout the year. The specimens were collected monthly, in Nacajuca, Tabasco state, Mexico. The results revealed strong annual variations in testicular volume, stages of the germ cells, and diameter and height of the epithelia of seminiferous tubules and efferent ducts. Recrudescence was detected from November to December, when initial mitotic activity of spermatogonia in the seminiferous tubules were observed, coinciding with the decrease of temperature, photoperiod and rainy season. From January to February, early spermatogenesis continued and early primary and secondary spermatocytes were developing within the seminiferous epithelium. From March through April, numerous spermatids in metamorphosis were observed. Spermiogenesis was completed from May through July, which coincided with an increase in temperature, photoperiod, and rainfall. Regression occurred from August through September when testicular volume and spermatogenic activity decreased. During this time, the seminiferous epithelium decreased in thickness, and germ cell recruitment ceased, only Sertoli cells and spermatogonia were present in the epithelium. Throughout testicular regression spermatocytes and spermatids disappeared and the presence of cellular debris, and scattered spermatozoa were observed in the lumen. The regressed testes presented the total suspension of spermatogenesis. During October, the seminiferous tubules contained only spermatogonia and Sertoli cells, and the size of the lumen was reduced, giving the appearance that it was occluded. In concert with testis development, the efferent ducts were packed with spermatozoa from May through August. The epididymis was devoid of spermatozoa by September. M. brachypoda exhibited a prenuptial pattern, in which spermatogenesis preceded the mating season. The seasonal cycle variations of spermatogenesis in M. brachypoda are the result of a single extended spermiation event, which is characteristic of reptilian species. J. Morphol. © 2012 Wiley Periodicals, Inc.     

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.     

Response of the seminiferous epithelium of the rat testis to withdrawal of androgen: evidence for direct effect upon intercellular spaces associated with Sertoli cell junctional complexes

The morphological response of the Sertoli cells to partial or complete withdrawal of testosterone was studied in adult rats following hypophysectomy or administration of ethane dimethanesulphonate (EDS), a toxicant known to destroy selectively the Leydig cells of the testis. To assess the role of germ cells in effecting changes to Sertoli cells following withdrawal of testosterone, germ cell-deficient rats with Sertoli-cell-only testes (SCO) were treated with EDS to remove the source of testosterone. At 6 days after hypophysectomy or 4,6 and 8 days after EDS treatment, stage VII and VIII seminiferous tubules showed degenerating germ cells and numerous basally-located vacuoles approximately 1–15 m in diameter. Ultrastructural analysis indicated that most of the vacuoles were multiple focal dilations of the intercellular space associated with Sertoli cell junctional complexes. In SCO rats, treatment with EDS resulted in a significant (P<0.05) increase in the formation of many vacuoles particularly in the base but also in the trunk of the Sertoli cells and again electron microscopic analysis showed multiple, localized expansions of the intercellular space associated with Sertoli cell junctional complexes. The appearance of intercellular spaces in SCO testes following androgen withdrawal cannot be attributed to shrinkage of degenerating germ cells since the seminiferous tubules did not contain germ cells. It is concluded that withdrawal of androgen induces early morphological alterations of the Sertoli cell junctional complexes in which the sites of membrane fusions representing tight junctions remain intact whereas the intercellular spaces exhibit major focal dilations. The results are discussed in relation to the fluid secretion by the seminiferous tubules which is regulated by the Sertoli cells.     

gamma-Tubulin overexpression in Sertoli cells in vivo. II: Retention of spermatids,residual bodies,and germ cell apoptosis

The degree of germ cell dependence on Sertoli cell-mediated activities has been a subject of considerable attention. Sertoli cell secretory pathways have been extensively studied both in an effort to understand their normal physiologic roles and as targets for pharmacologic and toxicant activity. To determine the degree to which normal spermatogenesis depends on key functions of the Sertoli cell microtubule network, adenoviral vectors that overexpress the microtubule nucleating protein, gamma-tubulin, were delivered to Sertoli cells in vivo. gamma-Tubulin overexpression disrupts the Sertoli cell microtubule network (as described in the companion article); leads to gross disorganization of the seminiferous epithelium, inducing retention of spermatids and residual bodies; and causes germ cell apoptosis. These data are consistent with earlier studies in which toxicants and pharmacologic agents were used to disrupt microtubule networks. These data confirm that Sertoli cell microtubule networks play an important role in maintaining the organization of the seminiferous epithelium and that in the absence of an intact Sertoli cell microtubule network, germ cell viability is impaired.     

Stage-specific effects of the fungicide carbendazim on Sertoli cell microtubules in rat testis

The aim of the present study is to provide a morphological explanation of carbendazim (CBZ)-induced sloughing of germ cells that occurs in a stage-specific manner. Therefore, very early alterations in the seminiferous tubule epithelium were examined histologically in the rat testis after oral administration of CBZ (400mg/kg). Gaps between the elongated and round spermatids, the first indication of germ cell sloughing (pre-sloughing), were observed in stage late VI-early VII seminiferous tubules at 90-min post-treatment. Tubulin immunoreaction in the Sertoli cells was reduced in intensity in tubules with pre-sloughing. However, electron microscopy demonstrated that there were some intact microtubules in these cells. At 120 min, sloughing was seen in stage late VI-early VII and XIII-XIV. Tubulin immunoreaction in the Sertoli cells was greatly decreased in intensity in tubules where cell sloughing was observed. Electron microscopy showed that there were few microtubules in the body region of these cells. Stages II-V and mid-VII-VIII were exempt from the sloughing effect at 180 min. These changes in microtubules were not observed in Sertoli cells that did not exhibit sloughing characteristics, regardless of the post-treatment intervals. The present results suggest that stage specificity of sloughing is due to the stage-specific susceptibility of Sertoli cell microtubules to CBZ.     

An ultrastructural study of the effect of a diabetogenic dose of alloxan on the secretory ameloblasts of the rat incisor

Sertoli cells of the ground squirrel (Spermophilus lateralis), a seasonal breeder, were examined by light and electron microscopy and their structure, particularly the organization of the cytoskeleton, was related to events that occur in the seminiferous epithelium during spermatogenesis. Among the events considered and described are the apical movement of elongate spermatids, withdrawal of residual cytoplasm from germ cells, transport of smooth endoplasmic reticulum (SER) between the base and apex of the Sertoli cells, and sperm release. These events are dramatically evident in this species because the seminiferous epithelium is thin, i.e., there are few germ cells, and both the germ cells and Sertoli cells are large. Sertoli cells of the ground squirrel have a remarkably well developed cytoskeleton. Microfilaments occur throughout the cell but are most evident in ectoplasmic specializations associated with junctions. Intermediate filaments occur around the nucleus, as a layer at the base of the cell, and adjacent to desmosome-like junctions with germ cells. Intermediate filaments, together with microtubules, are also abundant in regions of the cell involved with the transport of SER, in cytoplasm associated with elongate spermatids, and in processes that extend into the residual cytoplasm of germ cells. Our observations of ultrastructure are consistent with the hypothesis that Sertoli cell microtubules are involved with the movement of germ cells within the seminiferous epithelium, and further implicate these structures as possibly playing a role in the retraction of residual cytoplasm from germ cells and the intracellular transport of SER. The abundance and organization of intermediate filaments suggest that these cytoskeletal elements may also be involved with events that occur during spermatogenesis.     

Organ culture of human seminiferous tubules: A useful tool to study the role of nerve growth factor in the testis

Summary Seminiferous tubules from human testes were mechanically isolated, the cut edges were sealed, and the tubules were cultured in medium free of fetal calf serum (FCS). Degeneration of germ cells occurred during the culture period and was paralleled by a disruption of the seminiferous epithelium, a disturbance in morphology and function of Sertoli cells, and a thickening of the lamina propria. However, when tubules were cultured for 5 days in the presence of FCS, degeneration of the spermatogenic tissue was reduced. FCS increased the mitotic activity of germ cells, but did not maintain normal morphology and function of Sertoli cells and cellular elements of the lamina propria. The thickening of the tubular wall concurred with a change in phenotype of lamina-propria cells from myoid to fibroblastic. Addition of nerve growth factor (NGF) to the culture medium (i) maintained the myoid phenotype of lamina-propria cells, (ii) prevented thickening of the tubular wall, and (iii) stabilized Sertoli cell morphology and function. The effects of NGF appeared to depend on the trophic effects of FCS, since NGF alone had no influence on the maintenance of a regular morphology of the spermatogenic epithelium. The present results indicate a decisive role for NGF in stabilizing specific functions of seminiferous tubules.     

Fine structure of seminiferous tubules from prenatally irradiated rats

Summary The ultrastructure of the seminiferous tubules was studied in rats that had been subjected to whole body irradiation on the 19th day of gestation. The seminiferous tubules from 3 months-old irradiated animals are devoid of germ cells and contain only Sertoli cells. Compared with controls of the same age, the seminiferous tubule basal membrane is thickened and multilayered and several alterations are observed in the Sertoli cells. The most characteristic of these alterations are: (a) an abnormal number of nuclear heterochromatin clumps, (b) the presence of numerous cytoplasmic vacuoles and various sized lipid droplets, (c) elaborate interdigitations and junctions between adjacent cells, and (d) the presence of anomalous ectoplasmic specializations disposed perpendicularly to the Sertoli cell membrane.     

Identification of stage-specific proteins synthesized by rat seminiferous tubules

Experiments were conducted to determine how the cycle of the seminiferous epithelium influenced synthesis and secretion of proteins by seminiferous tubules. Tubular segments were treated with collagenase and then cultured with [35S]methionine. These myoid cell-depleted tubules isolated from different stages of the epithelial cycle exhibited, at Stages VI and XII, two distinct peaks of secretion of total radiolabeled proteins. Two-dimensional gel electrophoresis indicated that the patterns of secreted proteins from these two stages were remarkably different, while those from other stages were intermediate between those at the peaks. At least 15 proteins were secreted cyclically, many of them previously unrecognized products of the seminiferous epithelium. One product, designated Cyclic Protein-2 (CP-2), exhibited a pronounced cycle of secretion, its peak at Stage VI being 30-fold greater than at its nadir at Stages XII-XIV. Further investigation indicated that CP-2 did not appear to originate from myoid cells or dispersed germ cells but could be recovered from Sertoli cell-enriched cultures prepared from Stage VI tubules. Protein secretion by tubular segments was also characterized by immunoprecipitation with two polyspecific antisera directed against Sertoli cell products. Five secretory proteins were identified which had cycles different from one another and from CP-2. In contrast to secreted products, the synthesis of most cellular proteins by tubular segments remained relatively constant throughout the cycle. It is concluded: 1) segments of the seminiferous epithelium secrete proteins into the culture medium which are distinct from cellular proteins; 2) the synthesis of many of these proteins varies with the epithelial cycle; and 3) several of the secreted proteins are of Sertoli cell origin, including a newly identified protein, CP-2. This indicates that the morphology and the protein synthetic capacity of the seminiferous epithelium are coordinated over space and time.     

Observations on rat sertoli ectoplasmic (‘junctional’) specializations in their association with germ cells of the rat testis

The ectoplasmic (‘junctional’) specialization, a subsurface modification of the Sertoli cell that is often seen facing germ cells, was studied in relation to the development and maturation of these germ cells. This structure is composed of sub-surface bundles of filaments and more deeply placed endoplasmic reticulum. The data indicate that these subsurface modifications of Sertoli cells are reutilized in a cyclic fashion, being transferred from their position facing late spermatids to one opposing less mature germ cells. Ectoplasmic specializations appeared to function mechanically in grasping the heads of the spermatids which are undergoing the elongation and maturation phases of spermiogenesis rather than in actually attaching Sertoli cells to these germ cells. It is postulated that the ectoplasmic specialization imparts rigidity to that area of the Sertoli cell that surrounds the head region of the germ cell, forming a recess and a mantle by which the germ cell may be moved toward the base or toward the surface of the seminiferous epithelium. The observed linkage of microtubules to the cisternae of the complex provided a morphological basis for the changes in the cytoarchitecture of the Sertoli cell, which must accompany these movements.     

Relative volume of Sertoli cells in monkey seminiferous epithelium: a stereological analysis.

Techniques of quantitative stereology have been utilized to determine the relative volume occupied by the Sertoli cells and germ cells in two particular stages (I and VII) of the cycle of the seminiferous epithelium. Sertoli cell volume ranged from 24% in stage I of the cycle to 32% in stage VII. Early germ cells occupied 3.4% in stage I (spermatogonia) and 8.7% in stage VII (spermatogonia and preleptotene spermatocytes). Pachytene spermatocytes occupied 15% (Stage I) and 24% (stage VII) of the total volume of the seminiferous epithelium. In stage I the two generations of spermatids comprised 58% of the total epithelium by volume, whereas in stage VII, after spermiation, the acrosome phase spermatids occupied 35% of the total seminiferous epithelial volume.