Sertoli Cell Membrane Research Articles

Identification of insulin receptors on rat Sertoli cells

The binding of insulin to rat Sertoli cells was investigated to establish if effects of insulin on Sertoli cells can be mediated via insulin receptors. Sertoli cells were isolated from the testes of 3-week-old rats, and preincubated for 3 days in the absence of hormones. Binding of 125I-porcine insulin to the Sertoli cells was 75–80% specific and this binding was time- and pH-dependent and reversible. Scatchard analysis of the binding data resulted in curvilinear plots with a high affinity binding of K d = 1.8 × 10 −9 M. Porcine and bovine insulin competed equally well for 125I-porcine insulin binding. Porcine proinsulin was 10–50 times less potent, corresponding to its lower biological activity. Insulin-like growth factor-I (IGF-I) was 30–40 times less potent, indicating low affinity binding of IGF-I to the insulin receptor. Lutropin which was used as a control gave no competition with the 125I-insulin binding. Affinity labelling of Sertoli cell membrane proteins with 125I-insulin using the cross-linking agent disuccinimidylsuberate revealed binding of insulin to (a) protein(s) of M r > 300000 or M r = 130000 after electrophoresis under non-reducing or reducing conditions, respectively. Affinity labelling with 125I-insulin was largely prevented by unlabelled insulin. It is concluded that the protein of M r 130000 may represent the α-subunit of the insulin receptor. The presence of insulin receptors as well as IGF-I receptors on cultured rat Sertoli cells may suggest that insulin and IGF-I have specific functions in regulating the maturation and activities of Sertoli cells during the initiation and maintenance of spermatogenesis.

Guanine triphosphate-binding site regulation by follicle-stimulating hormone and guanine diphosphate in membranes from immature rat Sertoli cells.

GTP binding to Sertoli cell membranes has been investigated using [3H]5'-guanylyl-beta gamma-imidodiphosphate [[3H]Gpp(NH)p], a nonhydrolyzable analog of GTP. Binding of [3H]Gpp(NH)p Gpp(NH)p to membranes prepared from Sertoli cells in serum-free culture was proportional to membrane protein concentration in the range of 5-50 micrograms. Competitive displacement studies using adenine (ATP, ADP, and AMP) and guanine nucleotides [GTP, GDP, GMP, and Gpp(NH)p] indicated that only GTP, its analog Gpp(NH)p, and GDP were effective ligands. The relative potencies were Gpp(NH)p much greater than GTP greater than GDP, as characterized by ED50 values of 0.8, 2.5, and 4 microM, respectively. Competitive inhibition by GTP, however, was similar to that by Gpp(NH)p in the presence of a nucleoside triphosphate-regenerating system, suggesting the involvement of an active GTPase. Equilibrium binding studies indicated a single high affinity site for GTP with a Ka of 3.3 +/- 0.2 X 10(7) M-1. This value was supported by other studies in which an association rate constant of 1.8 X 10(6) M-1 min-1 and a dissociation rate constant of 2.4 X 10(-2) min-1 were estimated. Maximal binding of [3H]Gpp(NH)p to Sertoli cell membranes ranged from 30-55 pmol/mg protein. FSH enhanced [3H]Gpp(NH)p binding by about 50% (P less than 0.05), reflecting an increase in the number of available binding sites rather than an effect on Ka. When GDP was preincubated with membranes in the absence of FSH, the number of available binding sites for [3H]Gpp(NH)p was decreased. This reduction in available binding sites by pretreatment with GDP could be reversed by adding FSH during the equilibrium binding analysis. These studies have demonstrated specific high affinity binding of Gpp(NH)p to Sertoli cell membranes with an affinity comparable to that required for activation of FSH-sensitive adenylate cyclase. Furthermore, a potent GTPase activity associated with the Sertoli cell membrane is responsible for rapid hydrolysis of GTP to GDP and may participate in inactivation of GTP-dependent adenylate cyclase activity. The role of FSH in the regulation of nucleoside binding appears to be in facilitating exchange of GTP for GDP by enhancing the release of bound GDP.

Receptor-mediated endocytosis of transferrin by Sertoli cells of the rat.

Binding of 125I-transferrin (125I-Tf) to the plasma membrane of Sertoli cells and its endocytosis were analyzed by means of light- and electron-microscope quantitative radioautography. Five minutes after 125I-Tf was injected into the interstitial space of the testis, a strong labeling of the basal aspect of the seminiferous epithelium was observed in light-microscope radioautographs. Injection of the same dose of 125I-Tf plus a 200-fold excess of cold transferrin resulted in a marked diminution of the radioautographic reaction, indicating that the initial strong labeling with radiolabeled transferrin was specific. These results were consistent with the localization of immunoreactive fluorescence of transferrin receptor at the base of the seminiferous epithelium. In electron-microscope radioautographs of tubules collected at 5 min after injection, the membrane of Sertoli cells facing the basement membrane was well labeled with 125I-Tf. At 15 and 30 min, the plasma membrane was less intensely labeled, but the silver grains were then seen overlying multivesicular bodies with an electron-lucent matrix, identified as endosomes. This population of endosomes was always seen at a short distance from the basal membrane of Sertoli cells. At 90 min, no more labeling of the plasma membrane, endosomes, or any other cytoplasmic component was observed. Isolated seminiferous tubules and Sertoli cells labeled with 125I-Tf at 4 degrees C were rinsed and reincubated in a label-free medium at 37 degrees C for various periods of time from 5 to 90 min. A radioactive protein precipitated by trichloroacetic acid, presumably intact transferrin, was released from the tubules into the incubating medium; when measured, it was found to increase rapidly from 5 to 45 min and stabilize thereafter. These results suggest that transferrin was internalized by receptor-mediated endocytosis, reached endosomes, and then was released to the extratubular space. When native ferritin (NF), a tracer for fluid-phase endocytosis, was infused within the lumen of seminiferous tubules and 125I-Tf was simultaneously injected into the interstitial space, both markers rapidly reached different populations of endosomes. Endosomes labeled with NF, scattered throughout the cytoplasm, evolved with time into dense multivesicular bodies and secondary lysosomes, whereas radiolabeled transferrin reached only the endosomes located in the basal cytoplasm of Sertoli cells. The latter thus appeared to be principally involved in the uptake and recycling of transferrin.

Cyclic endocytic activity and kinetics of lysosomes in Sertoli cells of the rat: a morphometric analysis.

Native ferritin was injected into the rete testis of rats, and seminiferous tubules infused with the tracer were collected 6 h later and prepared for electron microscopic analysis. As a result of internalization of the tracer by Sertoli cells, label was found within 12-66% of the secondary lysosomes, depending on the stage of the cycle of the seminiferous epithelium. The Zeiss MOP-3 instrument was used on selected electron microscope photographs to measure a number of morphometric parameters. Applying appropriate formulae and a computerized program, it was possible to determine the absolute numbers of labeled and unlabeled secondary lysosomes per Sertoli cell for each one of the 14 stages of the cycle. Knowing the duration of these stages, it was also possible to evaluate the turnover kinetics and life span of lysosomes for each stage of the cycle. The percentage of ferritin-labeled lysosomes, regarded as an index of the endocytic activity of Sertoli cells, remained low in stages II to VIII, increased abruptly during stage IX, stayed high during stages X to XIV, and decreased to a low level during stage I of the following cycle. Correspondingly, the turnover of secondary lysosomes was relatively slow and their life span relatively long during stages II through VIII, while the turnover of lysosomes was faster and their life span shorter during stages X through XIV-I of the cycle. During stage IX, there was a sharp drop in the number of lysosomes per Sertoli cell associated with a fast rate of disappearance and a remarkably short life span of less than 4 h for the lysosomes. These features, characteristic of stage IX, are explained by the rapid fusion of lysosomes with residual bodies, which are phagocytosed by Sertoli cells at this particular stage of the cycle. The accelerated endocytosis taking place during stages IX through XIV of the cycle may explain the reduction of the surface area of the adluminal plasma membrane of Sertoli cells as well as the reduction in volume of the tubular lumen observed during these stages. Thus, the demonstrated cyclic endocytic activity of Sertoli cells and several other cyclical events taking place within seminiferous tubules correlate well.

Sertoli cell membrane polypeptide composition is modulated by germ cells

The polypeptide composition of Sertoli cell enriched cultures (SCEC) and Sertoli cell only cultures (SCOC) obtained after germ cell removal was investigated. Cells were labelled with [ 35S]methionine and analyzed by one and/or two-dimensional gel electrophoresis. The one-dimensional electrophoretic analysis of SCEC and SCOC particulate fraction did not show any appreciable difference between the two profiles. The more detailed two-dimensional electrophoretic analysis showed the appearance in SCOC of three polypeptides undetectable in SCEC. The molecular weight of these molecules ranged between 44 and 48 kDa. The effect of FSH on the Sertoli cell membrane composition was also investigated. No qualitative differences were detected, although the hormone increased many molecular species including the polypeptides appearing in SCOC. On the basis of these results, the hypothesis that germ cells influence Sertoli cell metabolic parameters is discussed.

Guanylate cyclase in the testis ofEsox luciusL. at time of spermiation: Histochemical and biochemical evidence

Abstract Guanylate cyclase activity has been studied biochemically and cytochemically in the testis of Esox lucius at the time of spermiation. The results of biochemical assays indicate that the specific activity of the soluble form is about three times higher than that of the paniculate form and that Mn++ is required for maximal enzyme activity. The cytochemical results demonstrate that the reaction product of guanylate cyclase is localized primarily on the plasma membranes of Sertoli cells and also on myoid and endothelial cells. This distribution of cyclase activity may indicate that this enzyme modulates the transfer of metabolites and hormones from the blood and/or lumen to Sertoli cells and vice versa.

A permeability barrier in the testis of an insect Triatoma: A freeze-fracture and lanthanum tracer study

In vertebrates, the testicular permeability barrier has been the subject of numerous studies. Some recent observations also indicate the existence of such a barrier in some invertebrates, e.g. insects and worms. With the aim of determining whether the morphological features of the blood-testis barrier generally found in vertebrates can be extended to other animals, we studied the testis of the insect Triatoma infestans using electron-dense tracers and freeze-fracture techniques. This organ is divided into cysts timed in synchroneous maturation. The intercellular tracer (lanthanum hydroxide) freely penetrates the basal areas of the seminiferous epithelium surrounding spermatogonia and spermatocytes devoid of synaptonemal complexes (pre-leptotene and leptone). Zygotene spermatocytes indicate the establishment of the barrier. Freeze-fracture techniques exhibit the morphological correlate of the barrier consisting of 9–10 nm particle rows on the P faces of the Sertoli cell membranes. These rows are relatively loose showing an undulating disposition and correspond to the septate junctions found in thin sections. The percolation of intercellular tracers demonstrates that septate junctions between the basal membraneous areas of Sertoli cells possess the barrier properties.

Stimulation of rat Sertoli cell adenylate cyclase by germ cells in vitro.

The effect of germ cells or germ cell fractions on adenylate cyclase (AC) activity in membrane preparations from cultured rat Sertoli cells has been examined. Whole germ cells or 30,000 X g pellet or supernatant fractions of germ cells have the ability to stimulate Sertoli cell AC to levels comparable to those measured in follicle-stimulating hormone-stimulated Sertoli cell membranes. Treatment at 100 degrees C but not 60 degrees C for 1 min abolished the ability of germ cell preparations to stimulate Sertoli AC. Germ cell stimulation of Sertoli cell AC was not calcium dependent, was not blocked by propranolol, and was observed to be dose dependent.

The role of a Sertoli cell actin-myosin system in sperm bundle formation in the ratfish, Hydrolagus colliei (Chondrichthyes, Holocephali).

Sertoli cells in the ratfish entirely surround a clone of spermatids to form a spermatocyst. As spermiogenesis proceeds within the cyst cavity, the acrosome areas become apposed to the Sertoli cell plasma membrane lining the spermatocyst. The spermatids elongate and are gathered into an increasingly compact bundle oriented with acrosomal tips directed toward the Sertoli cell base. As all acrosome areas move closer together, Sertoli cell microfilaments oriented parallel to the long spermatid axis appear and increase in concentration. Actin and myosin were demonstrated in the microfilament area with fluorescent antibodies and NBD-Phallacidin. Simultaneously, endocytosis of Sertoli cell membrane between spermatid attachment sites removes the intervening membrane and allows the latter sites to approach each other. Sertoli cell endocytosis is spatially and temporally related to a unique projection at the basal rim of each acrosome. During midspermiogenesis, structured intercellular material appears between the Sertoli cell and the acrosomal region of each spermatid. Its periodicity is closely related to periodic arrangement of Sertoli cell actin and material within the spermatids. These attachment sites move together upon endocytosis, gathering a clone of spermatids into a closely packed bundle.

Identification of a Spectrin-like Protein in Sertoli Cells 1

Sertoli cells prepared from rats ages 15 and 25 days were shown to contain a spectrin-like protein. Indirect immunofluorescence with monospecific antimouse erythrocyte immunoglobulin G (IgG) and with monospecific antimouse brain spectrin IgG revealed specific staining in Sertoli cells. Both antibodies precipitated two spectrin-like peptides of 240,000 and 235,000 daltons from cells solubilized with octyl glucoside. Proteins from Sertoli cell membranes were separated by electrophoresis on polyacrylamide gels containing sodium dodecyl sulfate and electrophoretically transferred to nitrocellulose membrane. Incubation of nitrocellulose membrane with either of the two antibodies, followed by horseradish peroxidase conjugated to second antibody, revealed only the larger, or alpha, spectrin subunit (Western blots). Both antibodies were used to provide immunoautoradiographic identification of the spectrin-like protein. In this procedure, spectrin and Sertoli cell membranes were shown to compete with [125I]-labeled spectrin from mouse erythrocytes for binding to antimouse erythrocyte spectrin IgG. Finally, two-dimensional proteolytic mapping of the 240,000- and 235,000-dalton peptides demonstrated limited spot homology with rat erythrocyte spectrin. However, subcellular fractions from Sertoli cells all contained a spectrin-like protein showing high homology from fraction to fraction. It is concluded that Sertoli cells contain a spectrin-like protein that is seen in cell fractions prepared by centrifugation, i.e., mitochondria, microsomes, nuclei, cytoplasm, and plasma membranes. Although homology with spectrin from erythrocytes or brain is not seen in peptide maps, the alpha subunit shares antigenic determinants with spectrin from erythrocytes. The beta subunit is believed to be precipitated by antispectrin as the result of binding to the alpha subunit, since the beta subunit shows no detectable antigenic homology with that of spectrin.

Isolation and characterization of Sertoli cell plasma membranes and associated plasminogen activator activity.

Plasma membranes were isolated from the cultured Sertoli cells of 20-day-old rat testes by differential centrifugation and sucrose density fractionation. The distribution and purity of subcellular components was determined by marker enzyme analysis of gradient fractions. The plasma membrane fraction showed an enrichment in two plasma membrane marker enzymes, 5'-nucleotidase and ouabain-sensitive Na+/K+-ATPase-specific activities, of 9- and 23-fold, respectively. Forty-two percent and 52% of the total cellular 5'-nucleotidase and ouabain-sensitive Na+/K+-ATPase activities, respectively, were found in the membrane fraction. The protein yield of plasma membrane was approximately 6% of the total cellular protein. Two-dimensional polyacrylamide gel electrophoresis was used to compare [35S] methionine- and [3H] glucosamine-labeled membrane proteins. The incorporation of [35S] methionine and [3H] glucosamine was increased in several proteins when the cultured Sertoli cells were treated with follicle-stimulating hormone, insulin, retinol, and testosterone. Isolated Sertoli cell membranes contained a membrane-associated form of plasminogen activator. Analysis of this plasminogen activator demonstrated that the membrane-associated enzyme existed primarily as a single 38,000-40,000-Mr form.

Morphological evidence for calcium stores at Sertoli-Sertoli and Sertoli-spermatid interrelations

Potassium pyroantimonate technique has been employed to localize calcium ultrastructurally at Sertoli-Sertoli and Sertoli-spermatid junctional specializations. Identification of Ca ++ as the major cation precipitated was performed by EGTA sensitivity and X-ray microprobe analysis. Ca ++deposits have been demonstrated in the endoplasmic reticulum cisternae underlying junctional complexes and along the plasma membranes of both Sertoli and germ cells.

Regulation of hormone-responsive Sertoli cell adenylyl cyclase in a cell-free system

Homologous desensitization of either FSH- or isoproterenol-responsive adenylyl cyclases in Sertoli cell membranes can be achieved in a cell-free system. Incubation of membrane particles from cultured immature Sertoli cells with either FSH or isoproterenol resulted in a time- and concentration-dependent loss of subsequent adenylyl cyclase response to the homologous hormone. Half-maximal refractoriness was achieved within 20–30 min of incubation. The concentration of FSH required to obtain half-maximal loss of adenylyl cyclase response (400 ng/ml) was in the same order of magnitude as the apparent K m for FSH-stimulated adenylyl cyclase activity (300 ng/ml). Hormone-induced homologous desensitization was dependent on the presence of both ATP and Mg 2+. Increasing concentrations of ATP in the presence of FSH caused a concentration-dependent loss of subsequent response to the homologous hormone. Halfmaximal desensitization was achieved at an ATP concentration of 0.2 mM. Increasing concentrations of Mg 2+ in the presence of either FSH or isoproterenol caused desensitization for the homologous hormone. The concentration of Mg 2+ giving half-maximal effect was approximately 5 mM in excess of ATP and EDTA. However, higher concentrations of free Mg 2+, in the absence of hormone, caused desensitization of both FSH- and isoproterenol-sensitive adenylyl cyclase with half-maximal effect at approximately 30 mM. Hormone-specific desensitization was obtained in the presence of GTP. However, when GTP was substituted with the non-hydrolysable analogue GMPP(NH)P the hormonal activation remained constant throughout 90 min of incubation. The hormone-induced refractoriness was probably not due to cAMP, since all incubations were performed in the presence of an excess of cAMP (1 mM) to block phosphodiesterase (PDE) activity. However, the finding that both ATP and Mg 2+ were required for hormone-induced desensitization suggests that the process may be mediated via a cAMP-independent phosphorylation reaction. Furthermore, the hormone appears to accelerate desensitization of the adenylyl cyclase system by increasing its sensitivity to the actions of Mg 2+.

The Actions of Insulin-Like Growth Factors I and II on Cultured Sertoli Cells*

Cultured Sertoli cells prepared from young rats (13 days old) showed increased incorporation of [3H]thymidine into DNA, increased production of lactate, and increased incorporation of [3H]leucine into protein in response to micromolar concentrations of insulin and nanomolar concentrations of insulin-like growth factor II (IGF-II). The first of these responses was also seen with nanomolar concentrations of IGF-I. Receptor affinity labeling studies using Sertoli cell membranes and whole Sertoli cells showed that these cells possess abundant growth factor receptors of type I (mol wt, 350,000) that show high affinity for IGF-I, moderate affinity for IGF-II, and low affinity for insulin. Sertoli cell membranes also show abundant growth factor receptors of type II (mol wt, 230,000) that show high affinity for IGF-II, moderate affinity for IGF-I, and no detectable affinity for insulin. Moreover, the responses of the Sertoli cell to insulin were observed at concentrations of 100 nM or higher, whereas insulin receptors are known to be saturated by insulin at concentrations of 10 nM or less. It is, therefore, concluded that Sertoli cells possess receptors for IGF-I and that the responses observed to insulin may result from binding of these hormones to receptors for IGF-I.

Cytochemical study on the distribution of adenylate cyclase in guinea pig testis.

The distribution of adenylate cyclase in testis, by means of a specific substrate adenylyl-imidodiphosphate (AMP-PNP), has been determined. Membrane-associated reaction products, indicative of adenylate cyclase activity, are localized by a complete cytochemical medium (containing 10 mM NaF) at the level of the basal compartment of the seminiferous epithelium, on the basal surface of Sertoli cells, and on adjacent plasma membranes of Sertoli cells and spermatogonial cells. At the level of the adluminal compartment, reaction products were found on adjacent plasma membranes of Sertoli cells and early or elongated spermatids. Adenylate cyclase reaction products are detectable by a basal incubation medium (without 10 mM NaF) only in the adluminal compartment on the spermatid plasma membranes.

Immunocytochemical staining of isolated rat Sertoli cells for anti-FSH beta.

Sertoli cells are a primary target for the action of follicle-stimulating hormone (FSH) in the testis. The purpose of this investigation was to verify ultrastructurally that FSH binds to receptors on the plasma membrane of isolated rat Sertoli cells. A relatively pure aliquot of Sertoli cells was obtained by first dissociating testicular tissue from immature rats with collagenase and then centrifuging the suspension in Percoll density gradients. Pre-embedding staining with the peroxidase anti-peroxidase (PAP) complex technique using anti-FSH beta as the primary antiserum localized endogenous receptor-bound FSH on the plasma membrane of isolated Sertoli cells. Staining was considered to be specific since membranes of Sertoli cells derived from hypophysectomized rats were not stained when subjected to the same procedure. Cytoplasmic vesicles in Sertoli cells from experimental, control, and hypophysectomized groups also stained with PAP. Staining of these structures appeared to be specific since it was obliterated by preabsorption of anti-FSH beta with FSH. Preabsorption with luteinizing hormone (LH) did not affect the staining of cytoplasmic vesicles. The results of this investigation provide the first evidence for ultrastructural localization of specific binding sites for anti-FSH beta on the cell membrane of isolated Sertoli cells using an unlabeled antibody technique, and they further support the contention that Sertoli cells are a primary target for the action of FSH.

Changes of sertoli cell glycoproteins induced by removal of the associated germ cells

Sertoli cell glycoproteins were studied in culture where these cells were in contact with germ cells (Sertoli cell enriched cultures, SCEC) and in pure Sertoli cell cultures. Sertoli cell only cultures (SCOC) were prepared by a short treatment of SCEC with hypotonic solution or by culturing seminiferous epithelium fragments from prenatally irradiated rats. After metabolic labeling with [3H]fucose. [14C]N-acetylglucosamine or [3H]leucine, SCEC and SCOC particulate fractions (105 000 g pellet) were analyzed by one-dimensional slab gel electrophoresis and fluorography. The comparison of the electrophoretic patterns obtained, demonstrated that a glycoprotein of MW 48 000, undetectable in SCEC, was present in SCOC after labelling with both sugar precursors. The MW 48 000 glycoprotein was also present in the electrophoretic profile of particulate fraction from [3H]fucos-labelled Sertoli cell cultures from prenatally irradiated rat. Such difference was not observed after labelling with [3H]leucine; in this experimental condition a MW 48 000 band was present in the electrophoretic profile of polypeptides from SCEC as well from SCOC. The synthesis of this glycoprotein represented a specific and stable cell response, since it occurred only a few hours after germ cell removal, and it was still detectable 3 days later. FSH stimulation did not influence the synthesis of the MW 48 000 glycoprotein, whereas it increased the synthesis of high MW glycoproteins. The hypothesis is discussed that the appearance of a new glycoprotein when Sertoli cells have lost their contact with germ cells could represent a product of glycosylation of preexisting molecules and their possible location in the Sertoli cell membrane. The results presented here provide additional evidence that Sertoli cell functions may be dependent on the association with the germ cell.

Varicose axons bearing "synaptic" vesicles on the basal lamina of the human seminiferous tubules.

Normal (infant and adult) and pathological testes were examined by electron microscopy in order to study testicular innervation. Nerves composed of non-myelinated fibres were abundant in the tunica vasculosa of the tunica albuginea. These nerves penetrated into the testicular septa reaching the interstitial tissue. This showed numerous non-myelinated nerve fibres running among the Leydig cells and blood vessels. Single axons or small groups of them, partially surrounded by Schwann cells, approached: 1) the Leydig cells, 2) the interstitial blood vessels, and 3) the seminiferous tubules. Single naked axons were also observed primarily in the proximity of the seminiferous tubules. These axons showed varicosities containing both small and large "synaptic" vesicles. The latter were less numerous and contained a central dense core. Small vesicles were agranular. Some varicose axons ran across the myofibroblast layer of the tunica propria reaching the basal lamina of the seminiferous tubules at the level of the Sertoli cells but not at the level of the spermatogonia. The intercellular space between Sertoli cell and axon membrane was about 150-200 nm.

Comparative observations on spermiogenesis

Abstract To extend the study on bird spermiogenesis we have observed by electron microscopy the mature testis of the cuculiform Crotophaga am. During nucleus elongation the chromatin condenses in dense granules and the nucleoplasm is reducing. The Golgi apparatus starts the developing of the acrosomal vesicle. The elongating nucleus drives the acrosomal vesicle against the cell membrane. At the opposite side the flagellum arises from the distal centriole and comes out from the cell at a very early stage. While the cytoplasm is reducing, the mitochondria arrange themselves around the distal centriole and around the fore part of the axoneme. The elongating spermatid does not have a microtubular manchette or a microtubular bundle, as seen in other birds. It is entirely surrounded by a Sertoli cell, which shows many microtubules scattered in the cytoplasm. These microtubules are arranged parallel to the axis of elongating spermatids. Near the Sertoli cell membrane, surrounding the acrosome, is electron-dense ...

Fine structure of seminiferous tubules from prenatally irradiated rats.

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.