A light microscopic and morphometric analysis of the Sertoli cell during the spermatogenic cycle of the rat

Overview of single-cell RNA sequencing analysis and its application to spermatogenesis research

Background

Single-cell transcriptomics allows parallel analysis of multiple cell types in tissues. Because testes comprise somatic cells and germ cells at various stages of spermatogenesis, single-cell RNA sequencing is a powerful tool for investigating the complex process of spermatogenesis. However, single-cell RNA sequencing analysis needs extensive knowledge of experimental technologies and bioinformatics, making it difficult for many, particularly experimental biologists and clinicians, to use it.

Methods

Aiming to make single-cell RNA sequencing analysis familiar, this review article presents an overview of experimental and computational methods for single-cell RNA sequencing analysis with a history of transcriptomics. In addition, combining the PubMed search and manual curation, this review also provides a summary of recent novel insights into human and mouse spermatogenesis obtained using single-cell RNA sequencing analyses.

Main Findings

Single-cell RNA sequencing identified mesenchymal cells and type II innate lymphoid cells as novel testicular cell types in the adult mouse testes, as well as detailed subtypes of germ cells. This review outlines recent discoveries into germ cell development and subtypes, somatic cell development, and cell-cell interactions.

Conclusion

The findings on spermatogenesis obtained using single-cell RNA sequencing may contribute to a deeper understanding of spermatogenesis and provide new directions for male fertility therapy.

Decoding the Spermatogenesis Program: New Insights from Transcriptomic Analyses

Spermatogenesis is a complex differentiation process coordinated spatiotemporally across and along seminiferous tubules. Cellular heterogeneity has made it challenging to obtain stage-specific molecular profiles of germ and somatic cells using bulk transcriptomic analyses. This has limited our ability to understand regulation of spermatogenesis and to integrate knowledge from model organisms to humans. The recent advancement of single-cell RNA-sequencing (scRNA-seq) technologies provides insights into the cell type diversity and molecular signatures in the testis. Fine-grained cell atlases of the testis contain both known and novel cell types and define the functional states along the germ cell developmental trajectory in many species. These atlases provide a reference system for integrated interspecies comparisons to discover mechanistic parallels and to enable future studies. Despite recent advances, we currently lack high-resolution data to probe germ cell-somatic cell interactions in the tissue environment, but the use of highly multiplexed spatial analysis technologies has begun to resolve this problem. Taken together, recent single-cell studies provide an improvedunderstanding of gametogenesis to examine underlying causes of infertility and enable the development of new therapeutic interventions.

Testicular dysgenesis syndrome and phthalate exposure: A review of literature

Endocrine disruptors are chemicals that interfere with the body's endocrine system and cause adverse effects in biological systems. Phthalates are a group of man-made chemicals which are mainly used as plasticizers and classified as endocrine disruptors. They are also used in cosmetic and personal care products as color or smell fixators. Moreover, phthalates are present in inks, adhesives, sealants, automobile parts, tools, toys, carpets, medical tubing and blood storage bags, and food packages. Pathological condition known as "testicular dysgenesis syndrome" (TDS) or "phthalate syndrome" is usually linked to phthalate exposure and is coined to describe the rise in alterations in reproductive health in men, such as reduced semen quality (decrease in sperm counts, sperm motility and increase in abnormal sperms), hypospadias, cryptorchidism, reduced anogenital distance and early-life testicular cancer. Phthalates are suggested to cause direct effect on gonadal and non-gonadal tissues, impair the differentiation and morphogenesis of seminiferous tubules and accessory sex organs and testicular cells (both Sertoli and Leydig cells), alter estradiol and/or testosterone levels, decrease insulin-like 3 (INSL3) peptide production, impair spermatogenesis and lead to epigenetic alterations, all of which may lead to TDS. This review will mainly focus on phthalates as causes of TDS and their mechanisms of action.

A Comprehensive Roadmap of Murine Spermatogenesis Defined by Single-Cell RNA-Seq

Spermatogenesis requires intricate interactions between the germline and somatic cells. Within a given cross section of a seminiferous tubule, multiple germ and somatic cell types co-occur. This cellular heterogeneity has made it difficult to profile distinct cell types at different stages of development. To address this challenge, we collected single-cell RNA sequencing data from ∼35,000 cells from the adult mouse testis and identified all known germ and somatic cells, as well as two unexpected somatic cell types. Our analysis revealed a continuous developmental trajectory of germ cells from spermatogonia to spermatids and identified candidate transcriptional regulators at several transition points during differentiation. Focused analyses delineated four subtypes of spermatogonia and nine subtypes of Sertoli cells; the latter linked to histologically defined developmental stages over the seminiferous epithelial cycle. Overall, this high-resolution cellular atlas represents a community resource and foundation of knowledge to study germ cell development and in vivo gametogenesis.

The Sertoli cell: one hundred fifty years of beauty and plasticity

It has been one and a half centuries since Enrico Sertoli published the seminal discovery of the testicular 'nurse cell', not only a key cell in the testis, but indeed one of the most amazing cells in the vertebrate body. In this review, we begin by examining the three phases of morphological research that have occurred in the study of Sertoli cells, because microscopic anatomy was essentially the only scientific discipline available for about the first 75 years after the discovery. Biochemistry and molecular biology then changed all of biological sciences, including our understanding of the functions of Sertoli cells. Immunology and stem cell biology were not even topics of science in 1865, but they have now become major issues in our appreciation of Sertoli cell's role in spermatogenesis. We end with the universal importance and plasticity of function by comparing Sertoli cells in fish, amphibians, and mammals. In these various classes of vertebrates, Sertoli cells have quite different modes of proliferation and epithelial maintenance, cystic vs. tubular formation, yet accomplish essentially the same function but in strikingly different ways.

Stage-specific gene expression is a fundamental characteristic of rat spermatogenic cells and Sertoli cells

Mammalian spermatogenesis is a complex biological process that occurs within a highly organized tissue, the seminiferous epithelium. The coordinated maturation of spermatogonia, spermatocytes, and spermatids suggests the existence of precise programs of gene expression in these cells and in their neighboring somatic Sertoli cells. The objective of this study was to identify the genes that execute these programs. Rat seminiferous tubules at stages I, II-III, IV-V, VI, VIIa,b, VIIc,d, VIII, IX-XI, XII, and XIII-XIV of the cycle were isolated by microdissection, whereas Sertoli cells, spermatogonia plus early spermatocytes, pachytene spermatocytes, and round spermatids were purified from enzymatically dispersed testes. Microarray analysis by using Rat Genome 230 2.0 arrays identified 16,971 probe sets that recognized testicular transcripts, and 398 of these were identified as testis-specific. Expression of 1,286 probe sets were found to differ at least 4-fold between two cell types and also across the stages of the cycle. Pathway and annotated cluster analyses of those probe sets predicted that entire biological pathways and processes are regulated cyclically in specific cells. Important among these are the cell cycle, DNA repair, and embryonic neuron development. Taken together, these data indicate that stage-regulated gene expression is a widespread and fundamental characteristic of spermatogenic cells and Sertoli cells.

Morphometric and ultrastructural analysis of stage-specific effects of Sertoli and spermatogenic cells seen after short-term testosterone treatment in young adult rat testes

The effects of testosterone treatment on spermatogenesis in the rat have been investigated by morphometric and structural analysis at the ultrastructural level in stages VII-IX. The aim has been to characterize the changes in Sertoli and spermatogenic cells to elucidate the mechanism of testosterone effects on spermatogenesis and to test the possibilities of developing male contraceptives. In stage VII, the morphometric parameters of volume and surface area in Sertoli cells (see abbreviations below): and the morphometric parameter of volume in the spermatogenic cells such as V(VPG,T), V(VPC,T), V(VrPT,T) and V(VelPT,T) decreased. In stage VIII, the respective values of Sertoli cells, VSN, and VSN/VSC decreased while SSJ increased, and the respective morphometric parameters in the spermatogenic cells, V(VPG,T), V(VPC,T), and V(VrPT,T) increased. In stage IX, in Sertoli cells VSC, VSN, VSN/VSC, and SSJ remained unchanged. In spermatogenic cells V(VPG,T), V(VPC,T), and V(VrPT,T) increased. Further, in all stages, a close apposition of mitochondria and rough endoplasmic reticulum in basolateral cytoplasm of Sertoli cells suggested active protein synthesis. In elongated spermatids in stage IX the microtubular manchette became disorganized. This disorganization and the unexpected shift after testosterone treatment from decrease in several morphometric parameters in stage VIII to increases in stage IX cannot be explained by alterations in testosterone (T), LH, FSH, and their respective receptors. Therefore, still unknown regulatory factors in spermatogenesis are apparently involved in the developmental interactions between Sertoli and spermatogenic cells.

Infection with Trypanosoma brucei potentiates the antifertility effect of gossypol, especially in the protein-malnourished male rat

Reproductive parameters were investigated in gossypol-treated male rats that had been infected experimentally with Trypanosoma brucei and then place on one of two diets of differing (low and normal) protein content. The endpoints assessed were reproductive organ weights, semen epididymal sperm counts, serum testosterone and histological, stereological and histomorphometric evaluation of the testis and accessory reproductive organs. Most of the parameters studied were lowest in the protein-malnourished, gossypol-treated, trypanosome-infected animals, when compared to those obtained from the corresponding animals that were only gossypol-treated or trypanosome-infected. Mean testicular size and the diameter and the total length of seminiferous tubules were especially reduced, indicating that the overall volume of the seminiferous epithelium in these animals was smaller. These findings suggest that reproductive capacity could be impaired in protein-malnourished, trypanosome-infected animals fed on gossypol-containing products, even when there are no obvious clinical signs of disease. This could translate into increased production costs in a farm enterprise. Screening for haemoparasitism would also seem to be worthwhile prior to evaluation and/or use of gossypol (or perhaps other potential contraceptives) in human subjects, especially in communities that are confronted with severe food shortages.

Efficiency of spermatogenesis

Spermatogenesis is a process of division and differentiation by which spermatozoa are produced in seminiferous tubules. A measure of efficiency of spermatogenesis is the estimated number of spermatozoa produced per day per gram of testicular parenchyma. This measure is not influenced by species differences in testicular size; however, it is influenced by species differences in the numerical density of germ cells and in the life spans of these cells. Seminiferous tubules are composed of somatic cells (myoid cells and Sertoli cells), and germ cells (spermatogonia, spermatocytes, and spermatids). Activity of these three germ cells divide spermatogenesis into spermatocytogenesis, meiosis, and spermiogenesis, respectively. Spermatocytegenesis 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 and yield four spermatids. Spermiogenesis is the differentiation of spherical spermatids into mature spermatids which are released at the luminal free surface as spermatozoa. The spermatogenic cycle is superimposed on the three major divisions of spermatogenesis. 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 impact occurs during spermatocytogenesis and meiosis. Efficiency of spermatogenesis is related to the amount of germ cell degeneration, pubertal development, season of the year, and aging of humans and animals. Number of Sertoli cells and amount of smooth endoplasmic reticulum of Leydig cells (but not Leydig cell number) are related to efficiency of spermatogenesis. In humans, efficiency of spermatogenesis is reflected in number of spermatogenic stages per cross-section and number of missing generations within each stage; however, the arrangement of stages along the tubular length does not reflect differences in the efficiency of spermatogenesis. In short, spermatogenesis involves both mitotic and meiotic cell divisions and an unsurpassed example of cell differentiation in the production of the spermatozoon, and daily sperm production per g parenchyma is a measure of its efficiency.

Building a testis

Specific cellular, subcellular and acellular components of the rat testis including the capsule, the peritubular tissue (tunica propria) and the lymphatic endothelium were analyzed using morphometric techniques at cellular and subcellular levels to yield volume and surface area data. These data were integrated with previously published data for other cellular components of the rat testis to provide information about the volumetric composition for virtually every component of this organ. For major cell types (Leydig, Sertoli, myoid cells and germ cells) the data are expressed to the subcellular level in terms of volume and, in some instances, surface area. Graphic portrayals of testis constituents are used for rapid visual understanding of testis structure. The data presented herein are useful in conjunction with biochemical data to describe physiological properties of cells and cell components and also for understanding how structure differs under experimental and in pathological situations.

Effect of seminiferous tubule size on hCG-induced regeneration of peritubular Leydig cells in hypophysectomized, EDS-treated rats

Following their selective destruction 3 weeks previously by administration of ethane dimethanesulphonate (EDS) the regenerative capacity of Leydig cells was assessed in relation to seminiferous tubule morphology in hypophysectomized adult rats administered 7 daily injections of 100 iu hCG. Total Leydig cell volume per testis in hCG-treated rats (30.2 +/- 3.2 microliters, mean +/- SEM) was significantly (p < 0.01) greater than in the testes of rats at 3 and 4 weeks after EDS-treatment (7.6 +/- 0.7 and 22.7 +/- 1.4 microliters, respectively). Regeneration of Leydig cells in hCG-treated rats significantly (p < 0.05) favoured peritubular locations (18.6 +/- 2.8 microliters/testis) compared to central or perivascular sites of origin (11.6 +/- 1.2 microliters/testis). Partial restoration of spermatogenesis occurred in hCG-treated rats (tubule diameters usually > 250 microns) and a significant inverse correlation was found between peritubular Leydig cell percentage, or total volume per testis, and the volumetric proportion of seminiferous tubules (r = -0.94, p < 0.001) or the seminiferous epithelium (r = -0.73 to -0.79, p < 0.05-0.01). No significant (p > 0.4-0.9) correlation existed between centrally-regenerated Leydig cells and these parameters. The results show that in response to hCG stimulation, Leydig cells are more likely to develop around smaller seminiferous tubules, suggesting that hCG alone cannot mimic the expected pattern of Leydig cell regeneration (central and peritubular origins) which occurs during normal sexual maturation or at 3-4 weeks after EDS treatment. It is concluded that other factors, possibly FSH, are required for typical Leydig cell development which in turn may be influenced by local cellular growth factors originating from either the seminiferous tubules or the adjacent intertubular tissue.

Sertoli cell nuclear changes in human testicular biopsies as revealed by three dimensional reconstruction

Serial semithin sections of human testicular biopsy material were used for three-dimensional reconstruction in order to obtain information about Sertoli cell nuclei in normal and pathologically altered seminiferous epithelia. The three dimensional reconstruction program is based on the triangulation of image point series. It includes a calculation modus for determining surfaces and an approximation formula for the estimation of volumes. Nuclei from the following specimens were reconstructed and for each the volume (v), surface (s), and a quotient (v/s), which is regarded as a marker for the degree of membrane infoldings, were calculated as follows: (1) For normal spermatogenesis (stage 1, 2, 3, 5; n = 18) v = 409.7 +/- 33.0 microns 3, s = 429.6 +/- 40.5 microns 2, v/s = 0.96 +/- 0.05.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of possible determinants and consequences of Leydig cell heterogeneity in man

Leydig cells in the human testis are highly heterogeneous, consisting of variably staining light and dark cells. The basis for this difference is unknown. The present study has assessed whether differing numbers or proportions of dark and light Leydig cells are related: (1) to the pronounced inter-individual variation in testosterone production by isolated Leydig cells, and (2) to differences in structural composition of the testis. Testes (paired weight 6.6-59.48 g) were obtained from 27 men aged 72.9 +/- 9.5 years (range 54-89 years) undergoing orchidectomy as primary treatment for prostatic cancer. Leydig cells were isolated by Percoll-purification and cultured for 20 h under basal and hCG-stimulated conditions. The proportion of light and dark Leydig cells isolated by this method was shown to reflect their proportions in situ, based on the morphometric analysis of fixed testicular tissue from the same men. Leydig cells isolated from all testes produced testosterone in vitro and responded to stimulation by hCG, though the amounts of testosterone produced varied widely between subjects. Because of the latter, samples were grouped into 'low' (n = 9), 'medium' (n = 11) and 'high' (n = 7) groups on the basis of their testosterone production. These groups did not differ in their age, testicular size or gross testicular morphology, though men in the 'high' group tended to have more total Leydig cells per testis. However, there was no overall correlation between testosterone production by isolated Leydig cells and the numbers of light or dark Leydig cells or their ratio or the total number of Leydig cells per testis. The relationship between the volume of light and dark Leydig cells and testicular composition was also assessed. The volume of both types of Leydig cells was strongly correlated (p < 0.001) with the volume of germ cells, but otherwise light and dark Leydig cells correlated positively with different structures. Thus, the volume of light Leydig cells correlated (p < 0.001) with the volume of blood vessels and of peritubular tissue whereas the volume of dark Leydig cells correlated (p < 0.01) with that of the tubular lumen. These differences could indicate differences in regulation and/or function of light and dark Leydig cells. However, the present data do not support the idea that light and dark Leydig cells may differ in their steroidogenic capacity.

Sertoli cell cycle: a re-examination of the structural changes during the cycle of the seminiferous epithelium of the rat

Seminiferous tubules in mammals are composed of cell associations that show a cyclic pattern of renewal and development. The cyclic nature of germ cell development suggests that the cells supporting the spermatogenic process, the Sertoli cells, might also differ structurally during the spermatogenic cycle in terms of the quantity of their constituents. In the present study, cyclic differences in volumes, and surface areas were determined using a sampling technique at the electron microscope level that proportionally samples the Sertoli cell within the seminiferous tubule. Among the many parameters studied, only the surface area of the cell, the volume of lipid, and the volume and surface area of the rough endoplasm reticulum were shown by statistical analysis to vary cyclically. Regarding rough endoplasm reticulum, the volume and surface area of this organelle peaked at mid-cycle and its low was recorded near the end of the cycle, exhibiting an approximate 15-fold difference between extremes. The rough endoplasm reticulum parameters generally correlated with known patterns of protein secretion within the tubule and with the secretion of specific proteins as well as the factors important in controlling protein secretion. Many Sertoli cell structural parameters suggested to be influenced cyclically in the rat in other studies could not be confirmed by the present study. Methodological differences in the present study and past studies are discussed as potential sources of error for these discrepancies.

Cathodoluminescence-emitting lipid droplets in rat testis: a study by analytical color fluorescence electron microscopy

Cathodoluminescence (CL) from lipid droplets (LDs) in the rat testis was examined by analytical color fluorescence electron microscopy. The results show that: (1) the CL at wavelengths of 320 nm (CL320) and 450 nm (CL450) is derived from cholesterol esters and a mixture of lipids including vitamin A esters, respectively; (2) CL320 in the LDs of Leydig cells sharply decreases on postnatal day 21, while CL320 and CL450 in the LDs of Sertoli cells begin to be detectable; (3) the CL450-emitting LDs in seminiferous tubules, whose distributional patterns display cyclic changes during the spermatogenic cycle, are involved in spermatogenesis; and (4) the intensity of CL as well as the distributional patterns of CL-emitting LDs in testicular cells change after hypophysectomy, vitamin-A deficiency, and treatment with ethylene dimethane sulfonate and testosterone propionate. This study demonstrates that analytical color fluorescence electron microscopy is a useful tool for in-vivo observation of some specific compounds which cannot be visualized by other methods.

Structural response of the hamster Sertoli cell to hypophysectomy: a correlative morphometric and endocrine study

Reproductively active hamsters were hypophysectomized and examined 6 or 20 days later in a combined morphometric and endocrine study of the Sertoli cell to determine 1) the morphological and endocrine effects of hypophysectomy of both short- and long-term duration, 2) if regression of Sertoli cells after hypophysectomy in a seasonal breeder resembles regression due to seasonal changes, and 3) if effects of hypophysectomy in a seasonal breeder are equivalent to the effects of hypophysectomy in a nonseasonal breeder. Six days after hypophysectomy, at a period when germ cell degeneration is first noted, there was a significant decrease in testis weight, interstitial space, tubule diameter and length, volume of seminiferous tubule, and tubular lumen. There were no significant changes in Sertoli cell nuclear and cytoplasmic volume although cell surface area was decreased significantly. Most organelles exhibited no significant change in volume or surface area except for secondary lysosomes which expectedly increased in volume as the result of phagocytosis of germinal cells. Thus at an early time period when functional changes in germ cells and Leydig cells are clearly evident (Russell et al. [1992] Endocrinology), the Sertoli cell shows minimal changes. Twenty days after hypophysectomy, the cell, nuclear and cytoplasmic volumes and surface area of the Sertoli cells, and volumes and surface areas of nearly all organelles were significantly decreased from values measured in normal and in short-term hypophysectomized hamsters. The exceptions were the total volumes of lipid which increased significantly and lysosomes which were similar to normal but significantly lower than short-term hypophysectomized animals. The long-term hypophysectomized hamster Sertoli cell, like that of the short-day hamster (Sinha Hikim et al. [1989b] Endocrinology, 125:1829-1843) is structurally regressed as a whole rather than exhibiting selective decreases in cellular and subcellular components. The size of the Sertoli cell in pituitary-intact, long- and short-term hypophysectomized animals showed positive and significant correlations with the volumes and surface areas of all its cytoplasmic organelles except the volume of lipid which showed a negative, significant correlation. Comparisons of long-term hypophysectomized hamsters (in long-day light exposure) and short-day exposed animals (Sinha Hikim et al. [1989b] (Endocrinology, 125:1829-1843) suggested that hypophysectomy, in general, resulted in similar, but slightly more severe regressive changes in the testis and germ cell population than those seen during seasonal regression.(ABSTRACT TRUNCATED AT 400 WORDS)

Testosterone and FSH have independent, synergistic and stage-dependent effects upon spermatogenesis in the rat testis

Adult rats were hypophysectomized and treated with ethane dimethanesulphonate (EDS) selectively to eliminate the Leydig cells in the testis. By removing the source of endogenous gonadotrophins and androgens, the subsequent effects on the seminiferous epithelium were studied after 20 days of treatment with vehicle, or FSH (2 x 50 micrograms/day) or a low dose of testosterone (0.6 mg testosterone esters every 3rd day) alone or in combination. Compared to vehicle-treated hypophysectomized rats with Leydig cells, testis weight in saline-treated hypophysectomized rats treated with EDS declined by 50%, spermatogenesis was disrupted severely and only 18% of the tubules contained spermatids, these being confined to stages I-VI of the spermatogenic cycle. Treatment with either FSH or testosterone esters alone significantly (P less than 0.01) increased testis weight compared to vehicle-treated hypophysectomized rats treated with EDS and 40% of tubules contained spermatids either at stages I-VI after FSH, or at all stages I-XIV after testosterone treatment. Treatment with FSH and testosterone esters together maintained testis weights approximately 20% above vehicle-treated hypophysectomized controls; over 70% of the seminiferous tubules contained spermatids and there was a marked stimulation of spermatogenesis at all stages of the spermatogenic cycle. The results suggest, that in the absence of the pituitary gland and the Leydig cells, FSH alone partially supports spermatogenesis up to the development of round spermatids whereas testosterone is capable of maintaining spermatid development at all 14 stages of the cycle. When FSH and testosterone were administered in combination, the effects upon spermatogenesis were far greater than the response expected if their individual effects were simply additive. It is therefore concluded that FSH may play a role in normal spermatogenesis and that this role is essentially that of augmenting the response of the testis to testosterone. The biochemical mechanisms via which this might occur are discussed and hypophysectomized rats treated with EDS used in the present studies should provide a useful approach for their identification.

Further observations of stage-specific effects seen after short-term hypophysectomy in the rat

Although hypophysectomy has been a popular tool to study the effects of hormone deprivation as well as concomitant or subsequent hormone supplementation, there is relatively little morphological information available on the structural manifestation of pituitary removal on the testis. In the report, changes, in addition to those previously reported after short-term (6 days) hypophysectomy in the rat (Russell and Clermont, 1977), are described. Membrane-bound vacuoles (primarily) appeared within the basal region of the Sertoli cell at approximately the level of Sertoli-Sertoli junctions. In stages VIII through XI elongating spermatids were abnormal and manifested manchette indentation of the nucleus, a variety of other abnormal head shapes, acrosomal breaks and enlargement of the subacrosomal space. These defects were interpreted as the effect of declining hormonal levels in stage VII on spermatids that had survived the stage VII hormone sensitivity known to occur with severe hormone depletion. Abnormalities in the flagellum involving the mitochondrial sheath and fibrous sheath were detected. Preleptotene spermatocytes degenerated and could be identified in the process of doing so near the base of the seminiferous epithelium. The contact of preleptotene spermatocytes with the basal lamina was also significantly reduced. The results show that both Sertoli cell and germ cell abnormalities were present although germ cell abnormalities could be a secondary consequence of lack of appropriate stimulation of the Sertoli cell. Degeneration of basal compartment germ cells shows that germ cells other than those located in the adluminal compartment are vulnerable to hormonal withdrawal. The question of how hormone effects are mediated in the testis at midcycle to produce these effects is discussed.

A comparative study in twelve mammalian species of volume densities, volumes, and numerical densities of selected testis components, emphasizing those related to the Sertoli cell

Morphometric studies were performed on 12 mammalian species (degu, dog, guinea pig, hamster, human, monkey, mouse, opossum, rabbit, rat, stallion, and woodchuck) to determine volume density percentage (Vv%), volume (V), and numerical density (Nv) of seminiferous tubule components, especially those related to the Sertoli cell, and to make species comparisons. For most species, measurements were taken both from stages where elongate spermatids were deeply embedded within the Sertoli cell and from stages near sperm release where elongate spermatids were in shallow crypts within the Sertoli cell. Montages, prepared from electron micrographs, were used to determine Vv% of Sertoli cell components in seminiferous tubules. Excluding the tubular lumen, the Sertoli cell occupied from a high of 43.1% (woodchuck) to a low of 14.0% (mouse) of the tubular epithelium. There was a strong negative correlation (r = -0.83; P less than 0.005) of volume occupancy of Sertoli cells with sperm production. Nuclear volume, as determined by serial reconstruction using serial thick sections, ranged from a high of 848.4 microns 3 (opossum) to a low of 273.8 microns 3 (degu). There was no correlation (r = 0.02) of nuclear volume with volume occupancy (Vv%) in the tubule. Sertoli cell volume was determined by point-counting morphometry at the electron-microscope level as the product of the nuclear size and points determined over the entire cell divided by points over the nucleus. Sertoli cell V ranged from 2,035.3 microns 3 (degu) to 7,011.6 microns 3 (opossum) and was highly correlated (r = 0.85; P less than 0.001) with nuclear size. However, there was no significant correlation between the Sertoli cell size (V) and volume occupancy (Vv%; r = 0.13) or sperm production (r = -0.21). Stereological estimates of the numerical density (Nv) of Sertoli cells ranged from a high of 101.9 x 10(6) (monkey) to a low of 24.9 x 10(6) (rabbit) cells per cm3 of testicular tissue. There was no correlation of numerical density of Sertoli cells with sperm production (r = 0.002). A negative correlation was, however, observed between the numerical density of the Sertoli cells and the Sertoli cell size (r = -0.79; P less than 0.002). Data from the present study are compared with those previously published. This is the first study to compare Sertoli cell morphological measurements using unbiased sampling techniques. Morphometric data are provided which will serve as a basis for other morphometric studies.

Possible role of elongated spermatids in control of stage-dependent changes in the diameter of the lumen of the rat seminiferous tubule

Adult male rats were treated with a single dose of 650 mg/kg methoxy acetic acid to deplete the seminiferous tubules specifically of pachytene and later spermatocytes. The effect of this treatment and the subsequent maturation-depletion of later germ cell types on the diameter of the seminiferous tubule and its lumen and the area of the seminiferous epithelium were studied in relation to the stages of the spermatogenic cycle. At 21 days after methoxy acetic acid treatment, the diameter of the tubule and the area of the epithelium were reduced below control values at all stages, consistent with the reduced number of early (stage VIII) or late (all other stages) spermatids. Unexpectedly, diameter of the lumen was also reduced at all stages other than VIII, and especially at stage VII. In controls, lumen diameter at stages VII and VIII was increased by approximately 50% compared with earlier and later stages. In rats treated 21 days previously with methoxy acetic acid no change occurred at stage VII (lacking elongated spermatids) while a normal increase did occur at stage VIII (lacking round but not elongated spermatids). At earlier times after methoxy acetic acid treatment when stage VII tubules were depleted of pachytene spermatocytes alone (3 days) or together with early spermatids (7 days), the diameter of the lumen was not significantly different from the control value. These data suggest that lumen diameter may be regulated by elongated spermatids, especially at stages VII and VIII.

An ultrastructural and morphometric analysis of the Sertoli cell during the spermatogenic cycle of the rat

The ultrastructure of Sertoli cells from selected stages of the spermatogenic cycle was assessed by morphometric analysis which showed significant changes in the morphological features of Sertoli cell cytoplasm at the commencement of the cycle (stage II) compared to the middle (stages VII-VIII) and the completion of the cycle (stages IX-XIV). Total volume and surface area of organelles (rough and smooth endoplasmic reticulum (ER), lysosomes, mitochondria and Golgi) exhibited stage-dependent and cyclic variations as did the total surface area of Sertoli cell plasma membrane. Polarization of cytoplasmic organelles to basal or columnar regions of the Sertoli cell, exhibited particularly by the Golgi, rough ER and lysosomes also showed marked cyclic fluctuations during the spermatogenic cycle. Rough and smooth ER exhibited the most dramatic stage-dependent changes in total volume and surface area the former being respectively largest and smallest in stages VII-VIII and XIII-XIV, the latter organelle presenting the reverse pattern in these two groups of stages. Similar stage-dependent alterations of lysosome volume and surface area were also noted, being maximal during stages XIII-XIV-II and reaching a nadir at stage VIII. Although the functional role of most Sertoli cell organelles and inclusions remain largely unknown, the present study suggests that the cyclic and stage-dependent variations in ultrastructure probably reflect major changes in Sertoli cell function necessary for the regulation of the spermatogenic cycle.