Dynamics of testicular germ cell proliferation in normal mice and transgenic mice overexpressing rat androgen-binding protein: a flow cytometric evaluation

Differential effect of visfatin inhibition on the testicular androgen and estrogen receptors expression in early pubertal mice

BACKGROUND

It is now well known that visfatin is expressed in the testis and ovary of various animals. Visfatin is known to regulate gonadal functions such as steroidogenesis, proliferation, and apoptosis in the ovary and testis of mice. Recently, we have shown that visfatin has an inhibitory role in the infantile mice testis. It has also been shown that visfatin stimulates testicular steroidogenesis in adult rats. However, the role of visfatin during puberty has not been investigated in relation to the above-mentioned process.

OBJECTIVE

The objective of the present study was to examine the effect of visfatin inhibition by FK866 from PND25 to PND35 (pre-pubertal to early pubertal) in male Swiss albino mice on steroidogenesis, proliferation, and apoptosis.

METHODS

Sixteen mice (25 days old) were divided into two groups, one group was given normal saline and the other group was administered with an inhibitor of visfatin (FK866) at the dose of 1.5 mg/kg by intraperitoneal injection for 10 days. Histopathological and immunohistochemical analysis, western blot analysis and hormonal assay were done.

RESULTS

Visfatin inhibition resulted in increased estrogen secretion, body weight, seminiferous tubule diameter, germinal epithelium height, and proliferation along with increased expression of BCl2, casapse3, ERs and aromatase expression in the mice testis. Visfatin inhibition down-regulated the testicular visfatin expression and also decreased abundance in the adipose tissues.

CONCLUSION

In conclusion, decreased AR expression and increased ERs expression by FK866, suggest that visfatin might have a stimulatory effect on AR signaling than ERs in the early pubertal stage of mice.

Preventing/Reversing Adverse Effects of Endocrine Disruption on Mouse Testes by Normalizing Tissue Resident VSELs

Reproductive health of men is declining in today's world due to increased developmental exposure to endocrine-disrupting chemicals (EDCs). We earlier reported that neonatal exposure to endocrine disruption resulted in reduced numbers of seminiferous tubules in Stage VIII, decreased sperm count, and infertility along with testicular tumors in 65% of diethylstilbestrol (DES) treated mice. Epigenetic changes due to EDCs, pushed the VSELs out of a quiescent state to enter cell cycle and undergo excessive self-renewal while transition of c-KIT- stem cells into c-KIT + germ cells was blocked due to altered MMR axis (Np95, Pcna, Dnmts), global hypomethylation (reduced expression of 5-methylcytosine) and loss of imprinting at Igf2-H19 and Dlk1-Meg3 loci. The present study was undertaken to firstly show similar defects in FACS sorted VSELs from DES treated testis and to further explore the reversal of these testicular pathologies by (i) oral administration of XAR (a nano-formulation of resveratrol) or (ii) inter-tubular transplantation of mesenchymal stromal cells (MSCs). Similar defects as reported earlier in the testes were evident, based on RNAseq data, on FACS sorted VSELs from DES treated mice. Both strategies were found effective, improved spermatogenesis, increased number of tubules in Stage VIII, normalized numbers of VSELs and c-KIT + cells, improved epigenetic status of VSELs to restore quiescent state, and reduced cancer incidence from 65% after DES to 13.33% and 20% after XAR treatment or MSCs transplantation respectively. Results provide a basis for initiating clinical studies and the study falls under the umbrella of United Nations Sustainable Development Goal 3 to ensure healthy lives and well-being for all of all ages.

Understanding the Underlying Molecular Mechanisms of Meiotic Arrest during In Vitro Spermatogenesis in Rat Prepubertal Testicular Tissue

In vitro spermatogenesis appears to be a promising approach to restore the fertility of childhood cancer survivors. The rat model has proven to be challenging, since germ cell maturation is arrested in organotypic cultures. Here, we report that, despite a meiotic entry, abnormal synaptonemal complexes were found in spermatocytes, and in vitro matured rat prepubertal testicular tissues displayed an immature phenotype. RNA-sequencing analyses highlighted up to 600 differentially expressed genes between in vitro and in vivo conditions, including genes involved in blood-testis barrier (BTB) formation and steroidogenesis. BTB integrity, the expression of two steroidogenic enzymes, and androgen receptors were indeed altered in vitro. Moreover, most of the top 10 predicted upstream regulators of deregulated genes were involved in inflammatory processes or immune cell recruitment. However, none of the three anti-inflammatory molecules tested in this study promoted meiotic progression. By analysing for the first time in vitro matured rat prepubertal testicular tissues at the molecular level, we uncovered the deregulation of several genes and revealed that defective BTB function, altered steroidogenic pathway, and probably inflammation, could be at the origin of meiotic arrest.

50 years of spermatogenesis: Sertoli cells and their interactions with germ cells

The complex morphology of the Sertoli cells and their interactions with germ cells has been a focus of investigators since they were first described by Enrico Sertoli. In the past 50 years, information on Sertoli cells has transcended morphology alone to become increasingly more focused on molecular questions. The goal of investigators has been to understand the role of the Sertoli cells in spermatogenesis and to apply that information to problems relating to male fertility. Sertoli cells are unique in that they are a nondividing cell population that is active for the reproductive lifetime of the animal and cyclically change morphology and gene expression. The numerous and distinctive junctional complexes and membrane specializations made by Sertoli cells provide a scaffold and environment for germ cell development. The increased focus of investigators on the molecular components and putative functions of testicular cells has resulted primarily from procedures that isolate specific cell types from the testicular milieu. Products of Sertoli cells that influence germ cell development and vice versa have been characterized from cultured cells and from the application of transgenic technologies. Germ cell transplantation has shown that the Sertoli cells respond to cues from germ cells with regard to developmental timing and has furthered a focus on spermatogenic stem cells and the stem cell niche. Very basic and universal features of spermatogenesis such as the cycle of the seminiferous epithelium and the spermatogenic wave are initiated by Sertoli cells and maintained by Sertoli-germ cell cooperation.

Testosterone Retention Mechanism in Sertoli Cells: A Biochemical Perspective

Mechanism(s) involved in regulating Intratesticular Testosterone levels (iT) have assumed importance in recent years, from the point of view of hormonal contraception. Contraceptives using Testosterone (T) in combination with Progestins (P), for more effective suppression of pituitary gonadotropins thereby iT, are not 100% effective in suppressing spermatogenesis in human males, likely due to pesrsistence of Intratesticular Dihydrotestosterone (iD) in poor-responders. Several lacunae pertaining to the mechanism of action of principal male hormone T during spermatogenesis remain to be resolved. Notably, the mechanism through which T brings about the stage-specific differentiation of germ cells lacking Androgen Receptors (AR). Testosterone is a highly anabolic steroid with a rapid tissue clearance rate. T is intratesticular substrate for synthesis of Dihydrotestosterone (DHT) and Estradiol (E2) involved in spermtaogenesis. Therefore, it is important to delineate the mechanism(s) for retention of iT, in order to understand regulation of its bioavailability in testis. In depth studies, pertaining to the role of androgen-binding protein(s) in sequestration, retention and bioavailability of T/DHT are required to understand male fertility regulation. The appropriate approach to overcome this lacuna would be development of mice lacking functional testicular Androgen-Binding Protein (ABPKO), but not deficient T/DHT, Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH), in order to understand its physiological functions. Insights gained about androgen retention mechanism(s) from the ABPKO murine model will be of immense help in improving the efficacy of male hormonal contraceptives and infertility management.

Curative GnRHa treatment has an unexpected repressive effect on Sertoli cell specific genes

Background

Follicle stimulating hormone and testosterone stimulate Sertoli cells to support germ cell function and differentiation. During mini-puberty, when gonadotropin (GnRH) stimulates increases in plasma luteinizing hormone (LH) and testosterone levels, gonocytes are transformed into Ad spermatogonia. In cryptorchidism, impaired gonadotropin secretion during mini-puberty results in insufficient LH and testosterone secretion, impaired gonocyte transition to Ad spermatogonia, and perturbed Sertoli cell proliferation. Treatment with a gonadotropin-releasing hormone agonist (GnRHa/Buserelin) induced gonocytes to differentiate into Ad spermatogonia and rescued fertility. The present study evaluated the impact of low LH secretion on Sertoli cell function by comparing differential gene expression data between testes with low LH that lacked Ad spermatogonia (Ad-) and testes that completed mini-puberty (Ad+). Furthermore, we analyzed changes in the transcription of selected Sertoli cell specific genes in response to GnRHa treatment.

Results

Ad- testes showed reduced expression of nine out of 40 selected Sertoli cell specific genes compared to Ad+ testes. GnRHa treatment repressed most of the Sertoli cell specific genes, including the inhibins, but it increased the expression of genes that regulate apoptosis (FASLG) and proliferation (GDNF).

Conclusions

Impaired-minipuberty with decreased LH and testosterone levels affected Ad and Sertoli cell development through positive and negative regulation of morphoregulatory and apoptotic genes. GnRHa treatment had a repressive effect on most Sertoli cell specific genes, which suggested that Sertoli cells underwent a cellular rearrangement. We propose that gonadotropin-dependent increases in FASLG and GDNF expression drove Sertoli cell proliferation and germ cell self-renewal and supported the transition of gonocytes to Ad spermatogonia, independent of inhibins.

The Magea gene cluster regulates male germ cell apoptosis without affecting the fertility in mice

While apoptosis is essential for male germ cell development, improper activation of apoptosis in the testis can affect spermatogenesis and cause reproduction defects. Members of the MAGE-A (melanoma antigen family A) gene family are frequently clustered in mammalian genomes and are exclusively expressed in the testes of normal animals but abnormally activated in a wide variety of cancers. We investigated the potential roles of these genes in spermatogenesis by generating a mouse model with a 210-kb genomic deletion encompassing six members of the Magea gene cluster (Magea1, Magea2, Magea3, Magea5, Magea6 and Magea8). Male mice carrying the deletion displayed smaller testes from 2 months old with a marked increase in apoptotic germ cells in the first wave of spermatogenesis. Furthermore, we found that Magea genes prevented stress-induced spermatogenic apoptosis after N-ethyl-N-nitrosourea (ENU) treatment during the adult stage. Mechanistically, deletion of the Magea gene cluster resulted in a dramatic increase in apoptotic germ cells, predominantly spermatocytes, with activation of p53 and induction of Bax in the testes. These observations demonstrate that the Magea genes are crucial in maintaining normal testicular size and protecting germ cells from excessive apoptosis under genotoxic stress.

Rictor Regulates Spermatogenesis by Controlling Sertoli Cell Cytoskeletal Organization and Cell Polarity in the Mouse Testis

Maintenance of cell polarity is essential for Sertoli cell and blood-testis barrier (BTB) function and spermatogenesis; however, the signaling mechanisms that regulate the integrity of the cytoskeleton and polarity of Sertoli cells are not fully understood. Here, we demonstrate that rapamycin-insensitive component of target of rapamycin (TOR) (Rictor), a core component of mechanistic TOR complex 2 (mTORC2), was expressed in the seminiferous epithelium during testicular development, and was down-regulated in a cadmium chloride-induced BTB damage model. We then conditionally deleted the Rictor gene in Sertoli cells and mutant mice exhibited azoospermia and were sterile as early as 3 months old. Further study revealed that Rictor may regulate actin organization via both mTORC2-dependent and mTORC2-independent mechanisms, in which the small GTPase, ras-related C3 botulinum toxin substrate 1, and phosphorylation of the actin filament regulatory protein, Paxillin, are involved, respectively. Loss of Rictor in Sertoli cells perturbed actin dynamics and caused microtubule disarrangement, both of which accumulatively disrupted Sertoli cell polarity and BTB integrity, accompanied by testicular developmental defects, spermiogenic arrest and excessive germ cell loss in mutant mice. Together, these findings establish the importance of Rictor/mTORC2 signaling in Sertoli cell function and spermatogenesis through the maintenance of Sertoli cell cytoskeletal dynamics, BTB integrity, and cell polarity.

Relaxin affects cell organization and early and late stages of spermatogenesis in a coculture of rat testicular cells

Relaxin and its receptor RXFP1 are co-expressed in Sertoli cells, and relaxin can stimulate proliferation of Sertoli cells. In this study, we investigated a role of relaxin in spermatogenesis, using a short-term culture of testicular cells of the rat that allowed differentiation of spermatogonia to spermatids. Sertoli, germ, and peritubular myoid cells were the predominant cell types in the culture. Sertoli and germ cells expressed RXFP1. Cultures were incubated without (control) or with 0.5% fetal bovine serum (FBS) or 100 ng/mL H2 relaxin (RLN) for 2 days. Cell organization, number, and differentiation were analyzed after 2 (D2), 5 (D5) or 8 (D8) days of culturing. Although the proportion of germ cells decayed from D2 to D5, the relative contribution of HC, 1C, 2C, and 4C germ cell populations remained constant in the control group during the whole culture. RLN did not affect the proportion of germ cell populations compared with control, but increased gene and/or protein expression of the undifferentiated and differentiated spermatogonia markers PLZF and c-KIT, and of the post-meiotic marker Odf2 in D5. RLN favored organization of cells in tubule-like structures, the arrangement of myoid cells around the tubules, arrangement of c-KIT-positive spermatogonia at the basal region of the tubules, and expression of the cell junction protein β-catenin close to the plasma membrane region. Knockdown of relaxin with small interfering RNA (siRNA) reduced expression of β-catenin at the cell junctions, and shifted its expression to the nucleus. We propose that relaxin may affect spermatogenesis by modulating spermatogonial self renewal and favoring cell contact.

Expression of histone H3 lysine 4 methylation and its demethylases in the developing mouse testis

Histone H3 lysine 4 methylation (H3K4me) is an epigenetic modification associated with gene activation and is dynamically regulated by histone methylases and demethylases. To date, the expression patterns of H3K4me and its demethylases in the developing testis remain unclear. The present study was designed to detect the expression of H3K4me1/2/3 and its demethylases LSD1, RBP2 and SMCX in 21-, 40- and 60-day-old mouse testes by using immunohistochemistry, quantitative real-time polymerase chain reaction (PCR) and Western blot. The immunohistochemical results demonstrated that the expression patterns of the same protein were similar in testes at different ages and that the positive staining cell types were mainly Leydig cells, type A and B spermatogonia, leptotene spermatocytes and spermatids for H3K4me1/2/3, Leydig cells, type A spermatogonia, zygotene and pachytene spermatocytes, spermatids, and Sertoli cells for LSD1 and type A and B spermatogonia for RBP2. Immunostaining for SMCX was not detected in testes. Quantitative real-time PCR and Western blot showed that the amounts of LSD1, RPB2 and SMCX mRNA and protein were age-dependent, were significantly reduced with increasing age and exhibited a negative correlation with the protein levels of H3K4me1/2/3. Thus, H3K4me, which is modified by its demethylases, probably plays a role in male spermatogenesis and testis development.

Histone acetylase inhibitor curcumin impairs mouse spermiogenesis-an in vitro study

In the previous study, we unraveled the unique “erasure strategy” during the mouse spermiogenesis. Chromatin associated proteins sequentially disassociated from the spermatid chromosome, which led to the termination of transcription in elongating spermatids. By this process, a relatively naïve paternal chromatin was generated, which might be essential for the zygotic development. We supposed the regulation of histone acetylation played an important role throughout this “erasure” process. In order to verify this hypothesis, we treated mouse spermatids in vitro by histone acetylase (HAT) inhibitor Curcumin. Our results showed an inhibiting effect of Curcumin on the growth of germ cell line in a dose-dependent manner. Accordingly, the apoptosis of primary haploid spermtids was increased by Curcumin treatment. As expected, the acetylated histone level was downregulated. Furthermore, we found the transcription in spermatids ceased in advance, the dynamics of chromatin associated factors was disturbed by Curcumin treatment. The regulation of histone acetylation should be one of the core reprogramming mechanisms during the spermiogenesis. The reproductive toxicity of Curcumin needs to be thoroughly investigated, which is crucial for its further clinical application.

Primordial germ cells (spermatogonial stem cells) of bullfrogs express sex hormone-binding globulin and steroid receptors during seasonal spermatogenesis

In vertebrate species, testosterone seems to inhibit spermatogonial differentiation and proliferation. However, this androgen can also be converted, via aromatase, into estrogen which stimulates spermatogonial differentiation and mitotic activity. During seasonal spermatogenesis of adult bullfrogs Lithobates catesbeianus, primordial germ cells (PGCs) show enhanced testosterone cytoplasm immunoexpression in winter; however, in summer, weak or no testosterone immunolabelling was observed. The aim of this study was to confirm if PGCs express stem cell markers - alkaline phosphatase (AP) activity and GFRα1 (glial-cell-line-derived neurotrophic factor) - and verify whether testosterone is maintained in these cells by androgen receptors (ARs) and/or sex hormone-binding globulin (SHBG) in winter. Furthermore, regarding the possibility that testosterone is converted into estrogen by PGCs in summer, the immunoexpression of estrogen receptor (ER)β was investigated. Bullfrog testes were collected in winter and in summer and were embedded in glycol methacrylate for morphological analyses or in paraffin for the histochemical detection of AP activity. GFRα1, AR, SHBG and ERβ expression were detected by Western blot and immunohistochemical analyses. The expression of AP activity and GFRα1 in the PGCs suggest that these cells are spermatogonial stem cells. In winter, the cytoplasmic immunoexpression of ARs and SHBG in the PGCs indicates that testosterone is maintained by these proteins in these cells. The cytoplasmic immunoexpression of ERβ, in summer, also points to an ER-mediated action of estrogen in PGCs. The results indicate a participation of testosterone and estrogen in the control of the primordial spermatogonia during the seasonal spermatogenesis of L. catesbeianus.

Targeted inactivation of nuclear interaction partner of ALK disrupts meiotic prophase

NIPA (nuclear interaction partner of ALK) is an F-box-like protein that monitors the timing of mitotic entry. Constitutively active NIPA delays mitotic entry by preventing accumulation of nuclear cyclin B1. Here, we have investigated the consequences of Nipa inactivation by using a conditional knockout strategy. Nipa-deficient animals are viable but show a lower birth rate and reduced body weight. Furthermore, Nipa-deficient males are sterile owing to a block of spermatogenesis during meiotic prophase. Whereas Nipa-/- mouse embryonic fibroblasts show no severe phenotype, Nipa-/- spermatocytes arrest during stage IV of the epithelial cycle with subsequent TUNEL-positive apoptosis resulting from improper synapsis, defects in the repair of DNA double-stranded breaks and synaptonemal complex formation. Moreover, we show nuclear accumulation of cyclin B1 with a subsequent premature increase in G2/M kinase activity in Nipa-/- spermatocytes. Together, these results reveal a novel role for NIPA in meiosis.

Diverse roles for sex hormone-binding globulin in reproduction

Sex hormone-binding globulin (SHBG) transports androgens and estrogens in blood and regulates their access to target tissues. Hepatic production of SHBG fluctuates throughout the life cycle and is influenced primarily by metabolic and hormonal factors. Genetic differences also contribute to interindividual variations in plasma SHBG levels. In addition to controlling the plasma distribution, metabolic clearance, and bioavailability of sex steroids, SHBG accumulates in the extravascular compartments of some tissues and in the cytoplasm of specific epithelial cells, where it exerts novel effects on androgen and estrogen action. In mammals, the gene-encoding SHBG is expressed primarily in the liver but also at low levels in other tissues, including the testis. In subprimate species, Shbg expression in Sertoli cells is under the control of follicle-stimulating hormone and produces the androgen-binding protein that influences androgen actions in the seminiferous tubules and epididymis. In humans, the SHBG gene is not expressed in Sertoli cells, but its expression in germ cells produces an SHBG isoform that accumulates in the acrosome. In fish, Shbg is produced by the liver but has a unique function in the gill as a portal for natural steroids and xenobiotics, including synthetic steroids. However, salmon have retained a second, poorly conserved Shbg gene that is expressed only in ovary, muscle, and gill and that likely exerts specialized functions in these tissues. The present review compares the production and functions of SHBG in different species and its diverse effects on reproduction.

Localization of ubiquitin specific protease 26 at blood-testis barrier and near Sertoli cell-germ cell interface in mouse testes

Ubiquitin Specific Protease 26 (USP26) is a little studied ubiquitin-specific protease that is expressed specifically in the testis. In humans, some USP26 polymorphisms have been reported to be associated with impaired male fertility. However, how USP26 affects male reproduction remains unclear. We generated an antibody that stained specifically cultured cells expressing an epitope-tagged USP26 and used it to elucidate the biological function of USP26. Immunostaining of mouse testis sections as well as dispersed germ cells showed the presence of USP26 at the blood-testis barrier, near the Sertoli cell-germ cell interface of post-step 7 spermatids, and coating the dorsal surface of sperm head. Further RT-PCR assays detected the expression of Usp26 in germ cells, but not in primary Sertoli cell lines. In addition, USP26 immunoprecipitated from testis lysates exhibited deubiquitinating activities. The localization of USP26 in the testis suggests a possible role in the movement of germ cells along the seminiferous epithelium.

Testis development, fertility, and survival in Ethanolamine kinase 2-deficient mice

Ethanolamine kinase 2 (Eki2) was previously isolated from a differential expression screen designed to identify candidate genes involved in testis development and differentiation. In mouse, Eki2 is specifically up-regulated in Sertoli cells of the developing testis at the time of sex determination. Based on this expression profile, Eki2 was considered a good candidate testis-determining gene. To investigate a possible role of Eki2 in testis development, we have generated a mouse with targeted disruption of the Eki2 gene by using an EGFP replacement strategy. No abnormalities were detected in the Eki2-deficient mice with regard to embryonic and adult testis morphology, differentiation, function, or fertility. Furthermore, no significant differences were observed in litter sizes, pup mortality rates, or distribution of the sexes among the offspring. Ethanolamine kinases are involved in the biosynthesis of phosphatidylethanolamine, a major membrane phospholipid. Expression analysis indicates that the absence of an apparent phenotype in the Eki2-deficient mice may be due to compensation by Eki2-family members or the activation of an alternative pathway to generate phosphatidylethanolamine. Expression of EGFP in this mouse model enabled the isolation of gonad cell populations, providing a useful resource from which to obtain relatively pure early steroidogenic cells for further studies.

DAZAP1, an hnRNP protein, is required for normal growth and spermatogenesis in mice

DAZAP1 (Deleted in Azoospermia Associated Protein 1) is a ubiquitous hnRNP protein that is expressed most abundantly in the testis. Its ability to shuttle between the nucleus and the cytoplasm and its exclusion from the transcriptionally inactive XY body in pachytene spermatocytes implicate it in mRNA transcription and transport. We generated Dazap1 mutant alleles to study the role of DAZAP1 in mouse development. Most mice homozygous for the null allele as well as a hypomorphic Fn allele died soon after birth. The few Dazap1(Fn/Fn) mice that survived could nonetheless live for more than a year. They appeared and behaved normally but were much smaller in size compared to their wild-type and heterozygous littermates. Both male and female Dazap1(Fn/Fn) mice were sterile. Males had small testes, and the seminiferous tubules were atrophic with increased numbers of apoptotic cells. The tubules contained many germ cells, including pachytene spermatocytes with visible XY-bodies and diplotene spermatocytes, but no post-meiotic cells. FACS analyses confirmed the absence of haploid germ cells, indicating spermatogenesis arrested right before the meiotic division. Female Dazap1(Fn/Fn) mice had small ovaries that contained normal-appearing follicles, yet their pregnancy produced no progeny due to failure in embryonic development. The phenotypes of Dazap1 mutant mice indicate that DAZAP1 is not only essential for spermatogenesis, but also required for the normal growth and development of mice.

Oligozoospermia with normal fertility in male mice lacking the androgen receptor in testis peritubular myoid cells

Androgens and the androgen receptor (AR) play important roles in the testes. Previously we have shown that male total AR knockout (T-AR-/y) mice revealed incomplete germ cell development and lowered serum testosterone levels, which resulted in azoospermia and infertility. However, the consequences of AR loss in particular types of testicular cells remain unclear. Using a Cre-loxP conditional knockout strategy, we generated a tissue-selective knockout mouse with the AR gene deleted in testis peritubular myoid cells (PM-AR-/y). Phenotype analyses showed that PM-AR-/y mice were indistinguishable from WT AR (AR+/y) mice with the exception of smaller testes size. PM-AR-/y mice have serum testosterone concentrations comparable with AR+/y mice. PM-AR-/y mice have oligozoospermia in the epididymis; however, fertility was normal. Although normal germ cell distribution ratio was found, total germ cell number decreased in PM-AR-/y mice. Further mechanistic studies demonstrated that PM-AR-/y mice have defects in the expression of Sertoli cells' functional marker genes such as tranferrin, epidermal fatty acid-binding protein, androgen-binding protein, and other junction genes including occludin, testin, nectin, zyxin, vinculin, laminingamma3, gelsolin, connection43, and N-cadherin. Furthermore, there were defects in peritubular myoid cell contractility-related genes such as endothelin-1, endothelin receptor A and B, adrenomedullin, adrenomedullin receptor, and vasopressin receptor 1a. Together, our PM-AR-/y mice provide in vivo evidence for the requirement of functional AR in peritubular myoid cells to maintain normal Sertoli cells function and peritubular myoid cell contractility, thus ensuring normal spermatogenesis and sperm output.

The androgen microenvironment of the human testis and hormonal control of spermatogenesis

It is well established for both rat and man that the total testosterone concentration within the testis is far higher than that in serum. We know for the rat that intratesticular testosterone can be reduced by 50-60% without an adverse effect on spermatogenesis but that the required intratesticular testosterone concentration is still 10-fold greater than serum testosterone concentration. This kind of information, if available for the human, could prove invaluable for understanding and treating select men with infertility and in the development of male hormonal contraceptives. Unfortunately, we know little about the androgen content of intratesticular fluid within the human testis and nothing about the relationship between intratesticular androgens and human spermatogenesis. Using a newly developed minimally invasive technique for repetitive testicular sampling, our recent studies of the human have demonstrated that, as in the rat, there is a gradient between the concentration of testosterone in serum and within the testis; intratesticular testosterone levels were found to be 100-fold higher than serum testosterone levels in normal men. Using liquid chromatography tandem mass spectroscopy, we have shown that intratesticular 5alpha-dihydrotestosterone (DHT) levels are only 2% that of testosterone and, thus, despite greater affinity for the androgen receptor, intratesticular DHT is not significant in normal men. In order to assess how much of the testosterone within the human testis is bioactive, we adapted a highly sensitive recombinant protein mammalian cell-based bioassay to measure androgen bioactivity. The androgen bioactivity in the normal human testis is roughly two-thirds that of the total testosterone measurable by radioimmunoassay, despite the fact that the concentrations of the major androgen-binding proteins (sex hormone-binding globulin- and androgen-binding protein) are insufficient to account for this difference. This finding suggests that androgens may bind to other, as-yet-unknown molecules in the human testis. How, or if, this relates to spermatogenesis in the rat, or to man-to-man differences in the response to hormonal contraceptives, is not clear. We do not yet know how much testosterone is required within the human testis to either maintain or restore quantitatively normal spermatogenesis because, as yet, experimental studies comparable to those performed in the rat have not been feasible for the human.

Estradiol affects androgen-binding protein expression and fertilizing ability of spermatozoa in adult male rats

The estrogenicity of certain environmental pollutants is being increasingly correlated to decline in sperm counts and fertility of the males. Qualitative effects, if any, of estrogen(s) on terminal differentiation of spermatids have been less reported. The present study suggests that exposure to estrogen(s) can also alter the status of condensed chromatin in testicular spermatozoa and reduce their fertilizing potential. A significant reduction was evident in the serum gonadotropins, testosterone, weights of reproductive organs, sperm counts and litters sired by male rats after 10 days of estradiol exposure to a dose of 0.1mg/kg/day. Estradiol treatment led to retardation of in vitro decondensation rates of sperm chromatin, reduction in the uptake of acridine orange dye by chromatin, reduction in susceptibility of chromatin to acid denaturation in vitro, reduced uptake of thiol reactive monobromobimane dye and reduced levels of immunoreactive protamine 1 in caput epididymal sperms. Concomitantly, testicular levels of immunoreactive protamine 1, transition proteins 1/2 and cyclic adenosyl response element modulator-tau (CREMtau) were significantly reduced whilst their mRNA levels were unaffected after estradiol treatment. A significant increase was observed in the testicular mRNA levels of androgen-binding protein (ABP) in estradiol treated sires. An inverse correlation was observed between ABP mRNA levels and uptake of acridine orange by estradiol treated caput sperm chromatin. The results suggest that estradiol-induced increase in ABP mRNA underlies the mechanism(s) involved in the reduction in levels of certain proteins involved in nuclear chromatin condensation during spermiogenesis.

Microarray analysis of androgen-regulated gene expression in testis: the use of the androgen-binding protein (ABP)-transgenic mouse as a model

BACKGROUND

Spermatogenesis is an androgen-dependent process, yet the molecular mechanisms of androgens' actions in testis are poorly understood. Transgenic mice overexpressing rat androgen-binding protein (ABP) in their testes have reduced levels of intratesticular androgens and, as a result, show a progressive impairment of spermatogenesis. We used this model to characterize changes in global gene expression in testis in response to reduced bioavailability of androgens.

METHODS

Total RNA was extracted from testes of 30-day old transgenic and wild-type control mice, converted to cRNA, labeled with biotin, and hybridized to oligonucleotide microarrays. Microarray results were confirmed by real-time reverse transcription polymerase chain reaction.

RESULTS

Three-hundred-eighty-one genes (3.05% of all transcripts represented on the chips) were up-regulated and 198 genes (1.59%) were down-regulated by at least a factor of 2 in the androgen-deficient animals compared to controls. Genes encoding membrane proteins, intracellular signaling molecules, enzymes, proteins participating in the immune response, and those involved in cytoskeleton organization were significantly overrepresented in the up-regulated group. Among the down-regulated transcripts, those coding for extracellular proteins were overrepresented most dramatically, followed by those related to proteolysis, cell adhesion, immune response, and growth factor, cytokine, and ion channel activities. Transcripts with the greatest potential impact on cellular activities included several transcription factors, intracellular signal transducers, secreted signaling molecules and enzymes, and various cell surface molecules. Major nodes in the up-regulated network were IL-6, AGT, MYC, and A2M, those in the down-regulated network were IL-2, -4, and -10, MAPK8, SOCS1, and CREB1.

CONCLUSION

Microarray analysis followed by gene ontology profiling and connectivity analysis identified several functional groups of genes and individual genes responding to sustained reduction of androgen levels in the mouse testis. These include genes whose products function as transcription factors, cell surface molecules including ion channels, extra- and intracellular signaling molecules, and secreted enzymes with the potential of regulating cell-to-cell attachment. The transcription factors CREB1 (down-regulated) and MYC (up-regulated) may mediate the most important initial phases of the testicular response to reduced levels of androgens. These results suggest specific avenues for further research that will lead to a better understanding of how androgens regulate spermatogenesis.

Spermatogenesis in testis primary cell cultures of the tilapia (Oreochromis niloticus)

Spermatogenesis in vertebrates is controlled by endocrine and paracrine factors and involves the communication between somatic and germ line cells. To elucidate some of the relevant factors in the complicated molecular control processes, we established an in vitro test system using primary cultures of tilapia (Oreochromis niloticus) testis cells. The cultures were enriched for germ line cells and Sertoli cells and largely depleted of spermatozoa. By staining the cells with propidium iodide and carboxyfluorescein succinimidyl ester (CFSE), different cell populations could be identified cytologically and, in addition, quantified by flow cytometry. Cells that had gone through one or more divisions could be identified unequivocally based on their CFSE staining intensity. In parallel cultures maintained for up to 16 days in the presence of 11-ketotestosterone (KT), insulin-like growth factor I (IGF), and/or human chorionic gonadotropin (hCG) the initiation of meiotic and mitotic divisions was monitored. Although KT was important for the initiation of meiosis, spermatogonial mitotic divisions between 10 days and 16 days of culture were promoted by IGF and/or hCG in the presence of KT. These results illustrate the potential of the established in vitro test system for the analysis of the molecular control mechanisms of spermatogenesis.

Estrogen Receptor β Expression and Apoptosis of Spermatocytes of Mice Overexpressing a Rat Androgen-Binding Protein Transgene1

Progression of the first meiotic division in male germ cells is regulated by a variety of factors, including androgens and possibly estrogens. When this regulation fails, meiosis is arrested and primary spermatocytes degenerate by apoptosis. Earlier studies showed that overexpression of rat androgen-binding protein (ABP) in the testis of transgenic mice results in a partial meiotic arrest and apoptosis of pachytene spermatocytes. In view of the recent localization of estrogen receptor beta (ERbeta) in primary spermatocytes and data suggesting the ability of ERbeta to repress cellular proliferation, we tested the hypothesis that variations in the testicular steroid microenvironment caused by excess ABP produce changes in ERbeta expression in this cellular type that could be associated to the meiotic arrest and, eventually, to the induction of germ cell apoptosis observed in the ABP transgenic mice. Increased levels of ERbeta mRNA and protein were demonstrated in the testis of rat ABP transgenic mice compared with nontransgenic littermates by reverse transcriptase-polymerase chain reaction (RT-PCR) experiments, Northern blotting, and Western Blotting. The major differences were found when isolated germ cells of transgenic and nontransgenic littermates were analyzed by RT-PCR. In keeping with this finding, ERbeta was strongly immunolabeled in pachytene spermatocytes of rat ABP transgenic mice and localized in tubular stages in which TUNEL labeling was maximal. Confocal microscopy analysis of a fluorescent TUNEL assay and ERbeta immunohistochemistry revealed that degenerating pachytene spermatocytes overexpressed ERbeta. The present results are consistent with the interpretation that ERbeta is associated with the events that regulate negatively the progression of meiosis or that lead to spermatocyte apoptosis.

Differential hormonal regulation of estrogen receptors ERalpha and ERbeta and androgen receptor expression in rat efferent ductules

Estrogen receptors, in addition to the androgen receptor (AR), are expressed at high levels in efferent ductules of the male reproductive tract and it is now well recognized that estrogen receptor (ER) alpha is required for the maintenance of normal structure and function of the ductules. However, little is known regarding the hormonal regulation of the receptors themselves in the male. In the present study, efferent ductule ligation and castration, followed by replacement with testosterone, dihydro-testosterone (DHT) or estradiol was used to investigate the relative importance of circulating and luminal sources of steroid for the modulation of ERalpha, ERbeta and AR in rat efferent ductules. Uni- or bilateral castration and ligation did not affect the expression of ERalpha and ERbeta, but bilateral castration caused down-regulation of AR. Replacement with DHT and testosterone alone or in combination with estradiol caused the recovery of AR expression to control levels. A slight recovery of AR was also observed after estrogen replacement. ERalpha expression was decreased to nearly undetectable levels after estrogen replacement. On the other hand, ERbeta did not show evident effects following any of the treatments, suggesting a constitutive expression of this receptor. This differential modulation of the steroid hormone receptors highlights the importance of maintaining a physiological androgen-estrogen balance to regulate the structure and function of efferent ductules in the male.

Dynamics of testicular germ cell apoptosis in normal mice and transgenic mice overexpressing rat androgen-binding protein

The number and type of testicular germ cells undergoing apoptosis in different age groups of mice (from 7 to 360 days of age) was determined and compared in age-matched wild type (WT) control and in a transgenic (TG) mice homozygous to rat androgen binding protein (ABP) using flow cytometry. Flow cytometric quantification revealed that the total number of germ cells undergoing apoptosis did not differ significantly in WT and TG mice up to Day 14. From Day 21 to Day 60, the number of germ cells undergoing apoptosis was consistently higher in TG than in WT mice. Starting from Day 90, the number of germ cells undergoing apoptosis in TG mice was lower than controls until Day 360. In 21-60 days old TG mice, spermatogonia, S-Phase cells, and primary spermatocytes are the cell types undergoing apoptosis at significantly greater numbers than those in WT mice. However, starting from day 60, the total number of spermatids undergoing apoptosis was significantly lower in TG mice than in age-matched WT controls. TdT-mediated dUTP-biotin nick end labeling (TUNEL) in testicular sections from TG mice of 21 and 30 days of age confirmed the presence of increased numbers of apoptotic germ cells compared to their age matched controls. These data indicate that the continuous presence of greater than physiological concentrations of ABP in the mouse testis has a biphasic effect on the frequency of apoptosis in germ cells. The initial pre-pubertal increase in testicular germ cell apoptosis may result from direct or indirect actions of ABP and is likely to determine the subsequent life-death balance of germ cell populations in TG mice, whereas the subsequent reduction may result from maturation depletion. A wave of apoptosis during the pre-pubertal period is required for normal spermatogenesis to develop, and our data indicate that this apoptotic wave may be regulated by ABP and/or androgens.