Infertility with defective spermatogenesis and hypotestosteronemia in male mice lacking the androgen receptor in Sertoli cells

Effects of aluminum exposure on serum sex hormones and androgen receptor expression in male rats

The effects of aluminum (Al) exposure on reproductive functions of male rats were investigated. Forty male Wistar rats (4 weeks old) weighing 75-95 g were randomly divided into four groups and orally exposed to 0 (control group GC), 64.18 (low-dose group GL), 128.36 (middle-dose group GM), and 256.72 (high-dose group GH) mg/kg aluminum trichloride in drinking water for 120 days. The levels of testosterone (T), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were determined by radioimmunoassay. The androgen receptor (AR) expressions in testes were detected respectively by immunohistochemistry and time quantitative PCR. Results showed that the levels of T and LH in GM and GH were lower than those in GC (P < 0.05), but there were no significant changes in FSH level in all Al-treated groups (P > 0.05). AR protein expressions in GM and GH were lower than those in GC (P < 0.05), and there was a dose-response relationship between Al-exposure doses and AR protein expressions. The levels of AR mRNA expressions were lower in all Al-treated groups than those of GC (P < 0.05). The results indicate that Al can cause endocrinal disorders and interfere with AR expression, which suppresses development and functional maintenance of the testes.

Notch signaling in Sertoli cells regulates cyclical gene expression of Hes1 but is dispensable for mouse spermatogenesis

Mammalian spermatogenesis is a highly regulated system dedicated to the continuous production of spermatozoa from spermatogonial stem cells, and the process largely depends on microenvironments created by Sertoli cells, unique somatic cells that reside within a seminiferous tubule. Spermatogenesis progresses with a cyclical program known as the "seminiferous epithelial cycle," which is accompanied with cyclical gene expression changes in Sertoli cells. However, it is unclear how the cyclicity in Sertoli cells is regulated. Here, we report that Notch signaling, which is known to play an important role for germ cell development in Drosophila and Caenorhabditis elegans, is cyclically activated in Sertoli cells and regulates stage-dependent gene expression of Hes1. To elucidate the regulatory mechanism of stage-dependent Hes1 expression and the role of Notch signaling in mouse spermatogenesis, we inactivated Notch signaling in Sertoli cells by deleting protein O-fucosyltransferase 1 (Pofut1), using the cre-loxP system, and found that stage-dependent Hes1 expression was dependent on the activation of Notch signaling. Unexpectedly, however, spermatogenesis proceeded normally. Our results thus indicate that Notch signaling regulates cyclical gene expression in Sertoli cells but is dispensable for mouse spermatogenesis. This highlights the evolutionary divergences in regulation of germ cell development.

Identification of testosterone-/androgen receptor-regulated genes in mouse Sertoli cells

Androgen and androgen receptor (AR) play important roles in male spermatogenesis and fertility, yet detailed androgen/AR signals in Sertoli cells remain unclear. To identify AR target genes in Sertoli cells, we analyzed the gene expression profiles of testis between mice lacking AR in Sertoli cells (S-AR(-/y)) and their littermate wild-type (WT) mice. Digital gene expression analysis identified 2276 genes downregulated and 2865 genes upregulated in the S-AR(-/y) mice testis compared to WT ones. To further nail down the difference within Sertoli cells, we first constructed Sertoli cell line TM4 with stably transfected AR (named as TM4/AR) and found androgens failed to transactivate AR in Sertoli TM4 and TM4/AR cells. Interestingly, additional transient transfection of AR-cDNA resulted in significant androgen responsiveness with TM4/AR cells showing 10 times more androgen sensitivity than TM4 cells. In the condition where maximal androgen response was demonstrated, we then analyzed gene expression and found the expression levels of 2313 genes were changed more than twofold by transient transfection of AR-cDNA in the presence of testosterone. Among these genes, 603 androgen-/AR-regulated genes, including 164 upregulated and 439 downregulated, were found in both S-AR(-/y) mice testis and TM4/AR cells. Using informatics analysis, the gene ontology was applied to analyze these androgen-/AR-regulated genes to predict the potential roles of androgen/AR in the process of spermatogenesis. Together, using gene analysis in both S-AR(-/y) mice testis and TM4/AR cells may help us to better understand the androgen/AR signals in Sertoli cells and their influences in spermatogenesis.

The development of an inducible androgen receptor knockout model in mouse to study the postmeiotic effects of androgens on germ cell development

A mouse model with a Sertoli cell (SC)-selective ablation of the androgen receptor (AR)-the SCARKO mouse-demonstrated that the effects of androgens on spermatogenesis depend on the presence of an active AR in SC. This model has been extremely valuable in the study of the effects of androgens on the initiation of spermatogenesis. However, due to the early (prenatal) inactivation of the AR SCARKO mice develop a complete block in meiosis, making it impossible to study the effects of androgens on postmeiotic steps of germ cell development. It would therefore be of interest to develop a model in which the AR can be ablated at any chosen time point. Here we used a mouse line ubiquitously expressing a tamoxifen (TM)-inducible Cre recombinase to develop an inducible AR knockout model (iARKO). It is shown that treatment with TM (3 mg/day) for five consecutive days efficiently inactivates the AR in testicular tissue and decreases the expression of known AR-target genes in SC (Rhox5, Spinlw1) without markedly affecting testicular cell composition one day after the final injection. TM treatment did, however, decrease serum gonadotropin levels and the expression of several Leydig cell genes (StAR, Cyp17a1, Insl3), resulting in decreased testosterone levels. Nevertheless, the intratesticular testosterone concentration still far exceeds the estimated concentrations required to saturate the AR. It may be concluded that the study of androgen-responsive postmeiotic genes in SC may be feasible using a TM-inducible AR knockout model provided that appropriate controls are included correcting for off-target effects of TM.

SOX9 and SF1 are involved in cyclic AMP-mediated upregulation of anti-Mullerian gene expression in the testicular prepubertal Sertoli cell line SMAT1

In Sertoli cells, anti-Müllerian hormone (AMH) expression is upregulated by FSH via cyclic AMP (cAMP), although no classical cAMP response elements exist in the AMH promoter. The response to cAMP involves NF-κB and AP2; however, targeted mutagenesis of their binding sites in the AMH promoter do not completely abolish the response. In this work we assessed whether SOX9, SF1, GATA4, and AP1 might represent alternative pathways involved in cAMP-mediated AMH upregulation, using real-time RT-PCR (qPCR), targeted mutagenesis, luciferase assays, and immunocytochemistry in the Sertoli cell line SMAT1. We also explored the signaling cascades potentially involved. In qPCR experiments, Amh, Sox9, Sf1, and Gata4 mRNA levels increased after SMAT1 cells were incubated with cAMP. Blocking PKA abolished the effect of cAMP on Sox9, Sf1, and Gata4 expression, inhibiting PI3K/PKB impaired the effect on Sf1 and Gata4, and reducing MEK1/2 and p38 MAPK activities curtailed Gata4 increase. SOX9 and SF1 translocated to the nucleus after incubation with cAMP. Mutations of the SOX9 or SF1 sites, but not of GAT4 or AP1 sites, precluded the response of a 3,063-bp AMH promoter to cAMP. In conclusion, in the Sertoli cell line SMAT1 cAMP upregulates SOX9, SF1, and GATA4 expression and induces SOX9 and SF1 nuclear translocation mainly through PKA, although other kinases may also participate. SOX9 and SF1 binding to the AMH promoter is essential to increase the activity of the AMH promoter in response to cAMP.

Effects of perinatal exposure to bisphenol A and di(2-ethylhexyl)-phthalate on gonadal development of male mice

PURPOSE

In this study, we investigated the effects of maternal transfer of bisphenol A (BPA) and di(2-ethylhexyl) phthalate (DEHP) during gestational and weaning periods on gonadal development of male offspring.

METHODS

Pregnant CD-1 mice were administered by gavages in corn oil with 0.1, 1, or 10 mg/kg/day of BPA and DEHP from gestational days (GD1-21) to the weaning period (postnatal days (PND) 1-21).

RESULTS

Our data indicated that the exposure significantly reduced the male-to-female sex ratio and the sizes of the gonads of male pups as recorded at PND15. The testes of the perinatally exposed male pups were developed less and the expression levels of testicular anti-mullerian hormone, androgen receptor, cyclin A, and StAR were significantly lesser than the control male pups. The less developed testes were accompanied with significant reductions in the expression levels of Gnrh and Fsh at the hypothalamic-pituitary levels. The negative effects were found to be persistent in the sexually mature pups at PND42.

CONCLUSION

Our data reveal that the maternal transfer of BPA and DEHP may impose negative influence on the development and functions of the reproductive system of male pups.

Maternal cypermethrin exposure during lactation impairs testicular development and spermatogenesis in male mouse offspring

Within the last decade, numerous epidemiological studies have demonstrated that endocrine disruptors are a possible cause for a decline in semen quality. Cypermethrin is a widely used pyrethroid insecticide, but little is known about its potentially adverse effects on male reproduction. In the present study, we investigated the effects of maternal cypermethrin exposure during lactation on testicular development and spermatogenesis in male offspring. Maternal mice were administered with cypermethrin (25 mg/kg) by gavage daily from postnatal day 0 (PND0) to PND21. Results showed that the weight of testes at PND21 was significantly decreased in pups whose mothers were exposed to cypermethrin during lactation. Maternal cypermethrin exposure during lactation markedly decreased the layers of spermatogenic cells, increased the inside diameter of seminiferous tubules, and disturbed the array of spermatogenic cells in testes of pups at PND21. In addition, maternal cypermethrin exposure during lactation markedly reduced mRNA and protein levels of testicular P450scc, a testosterone (T) synthetic enzyme. Correspondingly, the level of serum and testicular T at weaning was significantly decreased in pups whose mothers were exposed to cypermethrin during lactation. Although the expression of testicular T synthetic enzymes and serum and testicular T in adulthood had restored to control level, the decreased testicular weight and histological changes were irreversible. Importantly, the number of spermatozoa was significantly decreased in adult male offspring whose mothers were exposed to cypermethrin during lactation. In conclusion, maternal cypermethrin exposure during lactation permanently impairs testicular development and spermatogenesis in male offspring, whereas cypermethrin-induced endocrine disruption is reversible.

Testosterone administration to adult rats differentially modulates androgen and oestrogen receptor-α expression in reproductive organs and pituitary

Regulation of androgen receptor (AR) and oestrogen receptor α (ERα) expression has direct bearing on the physiology of male reproductive organs. With the help of three independent tools of immunohistochemistry, western blotting and RT-PCR, AR and ER α receptor expression was examined in the testis, epididymis, prostate, seminal vesicle and pituitary of adult rats following testosterone enanthate (TE, 3 mg/100 μl of olive oil/rat per week) intervention for 15 and 30 days. TE administration reduced AR immunoexpression which coincided well with the decline in the receptor protein and transcript levels. In contrast, ERα was found overexpressed in all the organs. While weights of testis and epididymis decreased significantly, those of prostate, seminal vesicle and pituitary demonstrated an upward trend. Spermatogenesis was adversely affected with decline in number of germ cells per tubule and increased prevalence of germ cell apoptosis. Increase in serum and decrease in intra-testicular levels of testosterone were found significant (P < 0.001) in both 15 and 30 days treatment groups. Serum follicle stimulating hormone declined significantly (P < 0.001) at the end of 30 days treatment. Taken together, the above findings indicate that the testosterone intervention differentially modulates, AR ERα expression, which is associated with hypospermatogenesis and increased germ cell apoptosis.

Sertoli cell-specific deletion of the androgen receptor compromises testicular immune privilege in mice

In the mammalian testis, meiotic and postmeiotic germ cell antigens are granted immune privilege. Both local immune suppression and specialized intercellular junctions between somatic Sertoli cells have been proposed to contribute to a highly restricted and effective blood-testis barrier (BTB) that helps maintain tolerance to germ cell antigens. Several studies have suggested that androgens play a role in immune suppression, although direct evidence for this is lacking. We previously reported that Sertoli cell-specific ablation of the androgen receptor (Ar) decreases expression of Cldn3, an androgen-regulated gene and component of Sertoli cell tight junctions, and increases the permeability of the BTB to biotin, a small-molecular-weight tracer. The physiological consequences of Sertoli cell-specific Ar (S-Ar) ablation on immune privilege are unknown. Here we show that in the testes of S-Ar mutant mice, the ultrastructure of Sertoli cell tight junctions is defective and testicular IgG levels are elevated. The interstitium of S-Ar mutant testes becomes populated with macrophages, neutrophils, plasma cells, and eosinophils, and serum samples of mutant mice contain antibodies against germ cell antigens. Together, these results suggest that Sertoli cell-specific deletion of the androgen receptor results in loss of testicular immune privilege. Suppressed levels of androgen signaling may be a contributing factor in idiopathic male infertility.

Gene expression alterations by conditional knockout of androgen receptor in adult Sertoli cells of Utp14b jsd/jsd (jsd) mice

Spermatogenesis is dependent primarily on testosterone action on the Sertoli cells, but the molecular mechanisms have not been identified. Attempts to identify testosterone-regulated target genes in Sertoli cells have used microarray analysis of gene expression in mice lacking the androgen receptor (AR) in Sertoli cells (SCARKO) and wild-type mice, but the analyses have been complicated both by alteration of germ cell composition of the testis when pubertal or adult mice were used and by differences in Sertoli-cell gene expression from the expression in adults when prepubertal mice were used. To overcome these limitations and identify AR-regulated genes in adult Sertoli cells, we compared gene expression in adult jsd (Utp14b jsd/jsd, juvenile spermatogonial depletion) mouse testes and with that in SCARKO-jsd mouse testes, since their cellular compositions are essentially identical, consisting of only type A spermatogonia and somatic cells. Microarray analysis identified 157 genes as downregulated and 197 genes as upregulated in the SCARKO-jsd mice compared to jsd mice. Some of the AR-regulated genes identified in the previous studies, including Rhox5, Drd4, and Fhod3, were also AR regulated in the jsd testes, but others, such as proteases and components of junctional complexes, were not AR regulated in our model. Surprisingly, a set of germ cell–specific genes preferentially expressed in differentiated spermatogonia and meiotic cells, including Meig1, Sycp3, and Ddx4, were all upregulated about 2-fold in SCARKO-jsd testes. AR-regulated genes in Sertoli cells must therefore be involved in the regulation of spermatogonial differentiation, although there was no significant differentiation to spermatocytes in SCARKO-jsd mice. Further gene ontogeny analysis revealed sets of genes whose changes in expression may be involved in the dislocation of Sertoli cell nuclei in SCARKO-jsd testes.

Defective survival of proliferating Sertoli cells and androgen receptor function in a mouse model of the ATR-X syndrome

X-linked ATR-X (alpha thalassemia, mental retardation, X-linked) syndrome in males is characterized by mental retardation, facial dysmorphism, alpha thalassemia and urogenital abnormalities, including small testes. It is unclear how mutations in the chromatin-remodeling protein ATRX cause these highly specific clinical features, since ATRX is widely expressed during organ development. To investigate the mechanisms underlying the testicular defects observed in ATR-X syndrome, we generated ScAtrxKO (Sertoli cell Atrx knockout) mice with Atrx specifically inactivated in the supporting cell lineage (Sertoli cells) of the mouse testis. ScAtrxKO mice developed small testes and discontinuous tubules, due to prolonged G2/M phase and apoptosis of proliferating Sertoli cells during fetal life. Apoptosis might be a consequence of the cell cycle defect. We also found that the onset of spermatogenesis was delayed in postnatal mice, with a range of spermatogenesis defects evident in adult ScAtrxKO mice. ATRX and the androgen receptor (AR) physically interact in the testis and in the Sertoli cell line TM4 and co-operatively activate the promoter of Rhox5, an important direct AR target. We also demonstrate that ATRX directly binds to the Rhox5 promoter in TM4 cells. Finally, gene expression of Rhox5 and of another AR-dependent gene, Spinlw1, was reduced in ScAtrxKO testes. These data suggest that ATRX can directly enhance the expression of androgen-dependent genes through physical interaction with AR. Recruitment of ATRX by DNA sequence-specific transcription factors could be a general mechanism by which ATRX achieves tissue-specific transcriptional regulation which could explain the highly specific clinical features of ATR-X syndrome when ATRX is mutated.

Nxf3 is expressed in Sertoli cells, but is dispensable for spermatogenesis

In eukaryotes, mRNA is actively exported to the cytoplasm by a family of nuclear RNA export factors (NXF). Four Nxf genes have been identified in the mouse: Nxf1, Nxf2, Nxf3, and Nxf7. Inactivation of Nxf2, a germ cell-specific gene, causes defects in spermatogenesis. Here we report that Nxf3 is expressed exclusively in Sertoli cells of the postnatal testis, in a developmentally regulated manner. Expression of Nxf3 coincides with the cessation of Sertoli cell proliferation and the beginning of their differentiation. Continued expression of Nxf3 in mature Sertoli cells of the adult is spermatogenesis stage-independent. Nxf3 is not essential for spermatogenesis, however, suggesting functional redundancy among Nxf family members. With its unique expression pattern in the testis, the promoter of Nxf3 can be used to drive postnatal Sertoli cell-specific expression of other proteins such as Cre recombinase.

Androgen receptor expression in the caput epididymal epithelium is essential for development of the initial segment and epididymal spermatozoa transit

The epididymis plays an essential role in male fertility, and disruption of epididymal function can lead to obstructive azoospermia. Formation and function of the epididymis is androgen-dependent. The androgen receptor (AR) is expressed in both the stromal and epithelial compartments of the epididymis, and androgen action mediated via stromal cells is vital for its normal development and function. However the impact of epithelial specific AR-dependent signaling in the epididymis remains underexplored. To address this, we used conditional gene-targeting in mice to selectively ablate AR from the caput epididymal epithelium, and characterized the resulting phenotype at multiple postnatal ages. Caput epithelium androgen receptor knock-out mice have normal serum testosterone concentrations at day (d) 21 and d100, but do not develop an epididymal initial segment. The remaining caput epithelium displays a significant decrease in epithelial cell height from d11 and lumen diameter from d21 and disruption of the smooth muscle layer of the caput epididymis at d100. From d21, caput epithelium androgen receptor knock-out mice accumulate cell debris, proteinaceous material, and, at later ages, spermatozoa in their efferent ducts, which prevents normal passage of spermatozoa from the testis into the cauda epididymis resulting in infertility when tested at d100. This efferent duct obstruction leads to fluid back-pressure and disruption of the seminiferous epithelium of the adult testis. We conclude that epithelial AR signaling is essential for postnatal development and function of the epididymal epithelium and that disruption of this signaling can contribute to obstructive azoospermia.

Role of ghrelin on testosterone secretion and the mRNA expression of androgen receptors in adult rat testis

The present study was designed to determine the effects of ghrelin on in vivo and in vitro secretion of testosterone (T) and the expression of androgen receptor (AR) mRNA in the adult rat testis. The distribution of growth hormone secretagogue receptors (GHS-R(1a)) in the testis was also investigated. GHS-R(1a) immunoreactivity presented mainly in Sertoli and Leydig cells, primary spermatocytes, and secondary spermatocytes. Adult rats that were intracerebroventricularly (i.c.v.) administrated different dosages (1 nmol and 3 nmol) of ghrelin could significantly inhibit the secretion of T. The experession of AR mRNA in the testis was also notably reduced with 3 nmol ghrelin. Additionaly, in vitro exposure of the Leydig cells to increasing concentrations of ghrelin resulted in no obvious changes of T secretion in the culture media and AR mRNA expression of Leydig cells. Overall, our data demonstrate that the i.c.v. injection of ghrelin plays a physiological role in T secretion and AR mRNA expression in the testis, further confirming the reproductive role of ghrelin.

Tissue-specific knockout of androgen receptor in mice

Androgen acting through the androgen receptor (AR) is known to be essential for male sexual differentiation and development. Using Cre-lox technology, we have generated the floxed AR mice, which have been bred with general or tissue-specific Cre expressing transgenic mice to knock out the AR gene in specific target cells. Our findings indicated that AR is required for sexual development and that loss of AR can have significant effects on many aspects of physiological functions and disease progression, such as immune function, metabolism, and tumorigenesis. Furthermore, our strategy can generate AR knockout (ARKO) in female mice, which allows researchers to study the AR function in the female. In brief, our floxed AR mouse model provides a powerful tool to study in vivo AR functions in selective tissues and cell types and has made possible several research breakthroughs in the field of endocrinology.

Regulation of Sertoli-germ cell adhesion and sperm release by FSH and nonclassical testosterone signaling

Testosterone and FSH act in synergy to produce the factors required to maximize the production of spermatozoa and male fertility. However, the molecular mechanisms by which these hormones support spermatogenesis are not well established. Recently, we identified a nonclassical mechanism of testosterone signaling in cultured rat Sertoli cells. We found that testosterone binding to the androgen receptor recruits and activates Src tyrosine kinase. Src then causes the activation of the epidermal growth factor receptor, which results in the phosphorylation and activation of the ERK MAPK and the cAMP response element-binding protein transcription factor. In this report, we find that FSH inhibits testosterone-mediated activation of ERK and the MAPK pathway in Sertoli cells via the protein kinase A-mediated inhibition of Raf kinase. In addition, FSH, as well as inhibitors of Src and ERK kinase activity, reduced germ cell attachment to Sertoli cells in culture. Using pathway-specific androgen receptor mutants we found that the nonclassical pathway is required for testosterone-mediated increases in germ cell attachment to Sertoli cells. Studies of seminiferous tubule explants determined that Src kinase, but not ERK kinase, activity is required for the release of sperm from seminiferous tubule explants. These findings suggest the nonclassical testosterone-signaling pathway acts via Src and ERK kinases to facilitate the adhesion of immature germ cells to Sertoli cells and through Src to permit the release of mature spermatozoa. In contrast, FSH acts to limit testosterone-mediated ERK kinase activity and germ cell attachment.

Selective ablation of the androgen receptor in mouse sertoli cells affects sertoli cell maturation, barrier formation and cytoskeletal development

The observation that mice with a selective ablation of the androgen receptor (AR) in Sertoli cells (SC) (SCARKO mice) display a complete block in meiosis supports the contention that SC play a pivotal role in the control of germ cell development by androgens. To delineate the physiological and molecular mechanism responsible for this control, we compared tubular development in pubertal SCARKO mice and littermate controls. Particular attention was paid to differences in SC maturation, SC barrier formation and cytoskeletal organization and to the molecular mediators potentially involved. Functional analysis of SC barrier development by hypertonic perfusion and lanthanum permeation techniques and immunohistochemical analysis of junction formation showed that SCARKO mice still attempt to produce a barrier separating basal and adluminal compartment but that barrier formation is delayed and defective. Defective barrier formation was accompanied by disturbances in SC nuclear maturation (immature shape, absence of prominent, tripartite nucleoli) and SC polarization (aberrant positioning of SC nuclei and cytoskeletal elements such as vimentin). Quantitative RT-PCR was used to study the transcript levels of genes potentially related to the described phenomena between day 8 and 35. Differences in the expression of SC genes known to play a role in junction formation could be shown from day 8 for Cldn11, from day 15 for Cldn3 and Espn, from day 20 for Cdh2 and Jam3 and from day 35 for ZO-1. Marked differences were also noted in the transcript levels of several genes that are also related to cell adhesion and cytoskeletal dynamics but that have not yet been studied in SC (Actn3, Ank3, Anxa9, Scin, Emb, Mpzl2). It is concluded that absence of a functional AR in SC impedes the remodeling of testicular tubules expected at the onset of spermatogenesis and interferes with the creation of the specific environment needed for germ cell development.

Androgen action via testicular arteriole smooth muscle cells is important for Leydig cell function, vasomotion and testicular fluid dynamics

Regulation of blood flow through the testicular microvasculature by vasomotion is thought to be important for normal testis function as it regulates interstitial fluid (IF) dynamics which is an important intra-testicular transport medium. Androgens control vasomotion, but how they exert these effects remains unclear. One possibility is by signalling via androgen receptors (AR) expressed in testicular arteriole smooth muscle cells. To investigate this and determine the overall importance of this mechanism in testis function, we generated a blood vessel smooth muscle cell-specific AR knockout mouse (SMARKO). Gross reproductive development was normal in SMARKO mice but testis weight was reduced in adulthood compared to control littermates; this reduction was not due to any changes in germ cell volume or to deficits in testosterone, LH or FSH concentrations and did not cause infertility. However, seminiferous tubule lumen volume was reduced in adult SMARKO males while interstitial volume was increased, perhaps indicating altered fluid dynamics; this was associated with compensated Leydig cell failure. Vasomotion was impaired in adult SMARKO males, though overall testis blood flow was normal and there was an increase in the overall blood vessel volume per testis in adult SMARKOs. In conclusion, these results indicate that ablating arteriole smooth muscle AR does not grossly alter spermatogenesis or affect male fertility but does subtly impair Leydig cell function and testicular fluid exchange, possibly by locally regulating microvascular blood flow within the testis.

Male germ cell apoptosis: regulation and biology

Cellular apoptosis appears to be a constant feature in the adult testis and during early development. This is essential because mammalian spermatogenesis is a complex process that requires precise homeostasis of different cell types. This review discusses the latest information available on male germ cell apoptosis induced by hormones, toxins and temperature in the context of the type of apoptotic pathway either the intrinsic or the extrinsic that may be used under a variety of stimuli. The review also discusses the importance of mechanisms pertaining to cellular apoptosis during testicular development, which is independent of exogenous stimuli. Since instances of germ cell carcinoma have increased over the past few decades, the current status of research on apoptotic pathways in teratocarcinoma cells is included. One other important aspect that is covered in this review is microRNA-mediated control of germ cell apoptosis, a field of research that is going to see intense activity in near future. Since knockout models of various kinds have been used to study many aspects of germ cell development, a comprehensive summary of literature on knockout mice used in reproduction studies is also provided.

Androgens and spermatogenesis: lessons from transgenic mouse models

Transgenic mouse models have contributed considerably to our understanding of the cellular and molecular mechanisms by which androgens control spermatogenesis. Cell-selective ablation of the androgen receptor (AR) in Sertoli cells (SC) results in a complete block in meiosis and unambiguously identifies the SC as the main cellular mediator of the effects of androgens on spermatogenesis. This conclusion is corroborated by similar knockouts in other potential testicular target cells. Mutations resulting in diminished expression of the AR or in alleles with increased length of the CAG repeat mimick specific human forms of disturbed fertility that are not accompanied by defects in male sexual development. Transcriptional profiling studies in mice with cell-selective and general knockouts of the AR, searching for androgen-regulated genes relevant to the control of spermatogenesis, have identified many candidate target genes. However, with the exception of Rhox5, the identified subsets of genes show little overlap. Genes related to tubular restructuring, cell junction dynamics, the cytoskeleton, solute transportation and vitamin A metabolism are prominently present. Further research will be needed to decide which of these genes are physiologically relevant and to identify genes that can be used as diagnostic tools or targets to modulate the effects of androgens in spermatogenesis.

Non-classical actions of testosterone and spermatogenesis

Testosterone is essential to maintain spermatogenesis and male fertility. In the absence of testosterone stimulation, spermatogenesis does not proceed beyond the meiosis stage. After withdrawal of testosterone, germ cells that have progressed beyond meiosis detach from supporting Sertoli cells and die, whereas mature sperm cannot be released from Sertoli cells resulting in infertility. The classical mechanism of testosterone action in which testosterone activates gene transcription by causing the androgen receptor to translocate to and bind specific DNA regulatory elements does not appear to fully explain testosterone regulation of spermatogenesis. This review discusses two non-classical testosterone signalling pathways in Sertoli cells and their potential effects on spermatogenesis. Specifically, testosterone-mediated activation of phospholipase C and calcium influx into Sertoli cells is described. Also, testosterone activation of Src, EGF receptor and ERK kinases as well as the activation of the CREB transcription factor and CREB-mediated transcription is reviewed. Regulation of germ cell adhesion to Sertoli cells and release of mature sperm from Sertoli cells by kinases regulated by the non-classical testosterone pathway is discussed. The evidence accumulated suggests that classical and non-classical testosterone signalling contribute to the maintenance of spermatogenesis and male fertility.

Transcription and post-transcriptional regulation of spermatogenesis

Spermatogenesis in mammals is achieved by multiple players that pursue a common goal of generating mature spermatozoa. The developmental processes acting on male germ cells that culminate in the production of the functional spermatozoa are regulated at both the transcription and post-transcriptional levels. This review addresses recent progress towards understanding such regulatory mechanisms and identifies future challenges to be addressed in this field. We focus on transcription factors, chromatin-associated factors and RNA-binding proteins necessary for spermatogenesis and/or sperm maturation. Understanding the molecular mechanisms that govern spermatogenesis has enormous implications for new contraceptive approaches and treatments for infertility.

Gene expression alterations by conditional knockout of androgen receptor in adult sertoli cells of Utp14b(jsd/jsd) (jsd) mice

Spermatogenesis is dependent primarily on testosterone action on the Sertoli cells, but the molecular mechanisms have not been identified. Attempts to identify testosterone-regulated target genes in Sertoli cells have used microarray analysis of gene expression in mice lacking the androgen receptor (AR) in Sertoli cells (SCARKO) and wild-type mice, but the analyses have been complicated both by alteration of germ cell composition of the testis when pubertal or adult mice were used and by differences in Sertoli-cell gene expression from the expression in adults when prepubertal mice were used. To overcome these limitations and identify AR-regulated genes in adult Sertoli cells, we compared gene expression in adult jsd (Utp14b(jsd/jsd), juvenile spermatogonial depletion) mouse testes and with that in SCARKO-jsd mouse testes, since their cellular compositions are essentially identical, consisting of only type A spermatogonia and somatic cells. Microarray analysis identified 157 genes as downregulated and 197 genes as upregulated in the SCARKO-jsd mice compared to jsd mice. Some of the AR-regulated genes identified in the previous studies, including Rhox5, Drd4, and Fhod3, were also AR regulated in the jsd testes, but others, such as proteases and components of junctional complexes, were not AR regulated in our model. Surprisingly, a set of germ cell-specific genes preferentially expressed in differentiated spermatogonia and meiotic cells, including Meig1, Sycp3, and Ddx4, were all upregulated about 2-fold in SCARKO-jsd testes. AR-regulated genes in Sertoli cells must therefore be involved in the regulation of spermatogonial differentiation, although there was no significant differentiation from spermatocytes in SCARKO-jsd mice. Further gene ontogeny analysis revealed sets of genes whose changes in expression may be involved in the dislocation of Sertoli cell nuclei in SCARKO-jsd testes.

Deletion of androgen receptor in the smooth muscle of the seminal vesicles impairs secretory function and alters its responsiveness to exogenous testosterone and estradiol

The seminal vesicles (SVs), like much of the male reproductive tract, depend on androgen-driven stromal-epithelial interactions for normal development, structure, and function. The primary function of the SVs is to synthesize proteins that contribute to the seminal plasma and this is androgen dependent. However, the cell-specific role for androgen action in adult SVs remains unclear. This study analyzed the SV in mice with targeted ablation of androgen receptors specifically in smooth muscle cells (PTM-ARKO) to determine in vivo whether it is androgen action in a subset of the SV stroma, the smooth muscle cells, that drives epithelial function and identity. These mice have significantly smaller SVs in adulthood with less smooth muscle and reduced epithelial cell height. Less epithelial cell proliferation was observed in adult PTM-ARKO SVs, compared with controls, and production of seminal proteins was reduced, indicating global impairment of epithelial cell function in PTM-ARKO SVs. None of these changes could be explained by altered serum testosterone or estradiol concentrations. We also demonstrate altered SV responsiveness to exogenous testosterone and estradiol in PTM-ARKO mice, indicating that smooth muscle androgen receptors may limit the SV epithelial proliferative response to exogenous estrogens. These results therefore demonstrate that the smooth muscle cells play a vital role in androgen-driven stromal-epithelial interactions in the SV, determining epithelial cell structure and function as well as limiting the SV epithelial proliferative response to exogenous estrogens.

A local autocrine axis in the testes that regulates spermatogenesis

Spermiation--the release of mature spermatozoa from Sertoli cells into the seminiferous tubule lumen--occurs by the disruption of an anchoring device known as the apical ectoplasmic specialization (apical ES). At the same time, the blood-testis barrier (BTB) undergoes extensive restructuring to facilitate the transit of preleptotene spermatocytes. While these two cellular events take place at opposite ends of the Sertoli cell epithelium, the events are in fact tightly coordinated, as any disruption in either process will lead to infertility. A local regulatory axis exists between the apical ES and the BTB in which biologically active laminin fragments produced at the apical ES by the action of matrix metalloproteinase 2 can regulate BTB restructuring directly or indirectly via the hemidesmosome. Equally important, polarity proteins play a crucial part in coordinating cellular events within this apical ES-BTB-hemidesmosome axis. Additionally, testosterone and cytokines work in concert to facilitate BTB restructuring, which enables the transit of spermatocytes while maintaining immunological barrier function. Herein, we will discuss this important autocrine-based cellular axis that parallels the hormonal-based hypothalamic-pituitary-testicular axis that regulates spermatogenesis. This local regulatory axis is the emerging target for male contraception.

Gonadotropin-regulated testicular RNA helicase (GRTH/DDX25) gene: cell-specific expression and transcriptional regulation by androgen in transgenic mouse testis

Gonadotropin-regulated testicular RNA helicase is a multifunctional enzyme present in both Leydig and germ cells that is essential for the progress of spermatogenesis. GRTH gene expression is transcriptionally upregulated by human chorionic gonadotropin (hCG) via second messenger (cAMP) and androgen in Leydig cells. The regulatory region(s) in the GRTH gene that is/are required for its cell-specific expression in the testis and hCG/androgen dependent expression were investigated in transgenic mice carrying sequential deletions of 5' flanking sequences of the GRTH gene. GFP-reporter gene expression directed by the GRTH 5' flanking sequences extending to -3.6 kb was specifically located in Leydig cells and the 205 bp minimal promoter domain was sufficient for this cell-specific expression. The 1 kb (5' to the ATG codon) transgene-directed expression was markedly increased by in vivo hCG treatment. Administration of the androgen receptor inhibitor Flutamide blocked the basal and hCG stimulated GFP expression in Leydig cells. We conclude that the expression of GRTH in testicular cells is differentially regulated by its 5' flanking sequence and that the 1 kb fragment of GRTH gene contains sequences for androgen regulation of its expression in Leydig cells.

Estradiol induction of spermatogenesis is mediated via an estrogen receptor-{alpha} mechanism involving neuroendocrine activation of follicle-stimulating hormone secretion

Both testosterone and its nonaromatizable metabolite dihydrotestosterone (DHT) induce spermatogenesis in gonadotropin-deficient hpg mice. Surprisingly, because aromatization is not required, estradiol (E2) also induces spermatogenesis and increases circulating FSH in hpg mice, but the mechanism remains unclear. We studied E2-induced spermatogenesis in hpg mice on an estrogen receptor (ER)-alpha (hpg/alphaERKO) or ERbeta (hpg/betaERKO) knockout or wild-type ER (hpg/WT) background treated with subdermal E2 or DHT implants for 6 wk. In hpg/WT and hpg/betaERKO, but not hpg/alphaERKO mice, E2 increased testis and epididymal weight, whereas DHT-induced increases were unaffected by ERalpha or ERbeta inactivation. E2 but not DHT treatment increased serum FSH (but not LH) in hpg/WT and hpg/betaERKO but not hpg/alphaERKO hpg mice. DHT or E2 alone increased (premeiotic) spermatogonia and (meiotic) spermatocytes without significant change in Sertoli cell numbers. DHT alone increased postmeiotic spermatids, regardless of ER presence, compared with variable ERalpha-dependent E2 postmeiotic responses. An ERalpha-mediated effect was confirmed by treating hpg mice for 6 wk by subdermal selective ER-alpha (16alpha-LE(2)) or ERbeta (8beta-VE(2)) agonist implants. ERalpha (but not ERbeta) agonist increased testis and epididymal weight, Sertoli cell, spermatogonia, meiotic, and postmeiotic germ cell numbers. Only ERalpha agonist markedly increased serum FSH, whereas either agonist induced small rises in serum LH. Administration of ERalpha agonist or E2 in the presence of functional ERalpha induced prominent gene expression of specific Sertoli (Eppin, Rhox5) and Leydig cell (Cyp11a1, Hsd3b1) markers. We conclude that E2-induced spermatogenesis in hpg mice involves an ERalpha-dependent neuroendocrine mechanism increasing blood FSH and Sertoli cell function.

Local signalling environments and human male infertility: what we can learn from mouse models

Infertility is one of the most prevalent public health problems facing young adult males in today's society. A clear, treatable cause of infertility cannot be determined in a large number of these patients, and a growing body of evidence suggests that infertility in many of these men may be due to genetic causes. Studies using mouse knockout technology have been integral for examination of normal spermatogenesis and to identify proteins essential for this process, which in turn are candidate genes for human male infertility. Successful spermatogenesis depends on a delicate balance of local signalling factors, and this review focuses on the genes that encode these factors. Normal functioning of all testicular cell types is essential for fertility and might also be crucial to prevent germ cell oncogenesis. Analysis of these signalling processes in spermatogenesis using mouse models has provided investigators with an invaluable tool to effectively translate basic science research to the research of human disease and infertility.

Direct action through the sertoli cells is essential for androgen stimulation of spermatogenesis

Androgens act to stimulate spermatogenesis through androgen receptors (ARs) on the Sertoli cells and peritubular myoid cells. Specific ablation of the AR in either cell type will cause a severe disruption of spermatogenesis. To determine whether androgens can stimulate spermatogenesis through direct action on the peritubular myoid cells alone or whether action on the Sertoli cells is essential, we crossed hypogonadal (hpg) mice that lack gonadotrophins and intratesticular androgen with mice lacking ARs either ubiquitously (ARKO) or specifically on the Sertoli cells (SCARKO). These hpg.ARKO and hpg.SCARKO mice were treated with testosterone (T) or dihydrotestosterone (DHT) for 7 d and testicular morphology and cell numbers assessed. Androgen treatment did not affect Sertoli cell numbers in any animal group. Both T and DHT increased numbers of spermatogonia and spermatocytes in hpg mice, but DHT has no effect on germ cell numbers in hpg.SCARKO and hpg.ARKO mice. T increased germ cell numbers in hpg.SCARKO and hpg.ARKO mice, but this was associated with stimulation of FSH release. Results show that androgen stimulation of spermatogenesis requires direct androgen action on the Sertoli cells.

The Rhox genes

Homeobox genes encode transcription factors that have crucial roles in embryogenesis. A recently discovered set of homeobox genes--the Rhox genes--are expressed during both embryogenesis and in adult reproductive tissues. The 33 known mouse Rhox genes are clustered together in a single region on the X chromosome, while likely descendents of the primodial Rhox cluster, Arx and Esx1, have moved to other positions on the X chromosome. Here, we summarize what is known about the regulation and function of Rhox cluster and Rhox-related genes during embryogenesis and gametogenesis. The founding member of the Rhox gene cluster--Rhox5 (previously known as Pem)--has been studied in the most depth and thus is the focus of this review. We also discuss the unusually rapid evolution of the Rhox gene cluster.

Alterations in the steroid hormone receptor co-chaperone FKBPL are associated with male infertility: a case-control study

BACKGROUND

Male infertility is a common cause of reproductive failure in humans. In mice, targeted deletions of the genes coding for FKBP6 or FKBP52, members of the FK506 binding protein family, can result in male infertility. In the case of FKBP52, this reflects an important role in potentiating Androgen Receptor (AR) signalling in the prostate and accessory glands, but not the testis. In infertile men, no mutations of FKBP52 or FKBP6 have been found so far, but the gene for FKBP-like (FKBPL) maps to chromosome 6p21.3, an area linked to azoospermia in a group of Japanese patients.

METHODS

To determine whether mutations in FKBPL could contribute to the azoospermic phenotype, we examined expression in mouse and human tissues by RNA array blot, RT-PCR and immunohistochemistry and sequenced the complete gene from two azoospermic patient cohorts and matching control groups. FKBPL-AR interaction was assayed using reporter constructs in vitro.

RESULTS

FKBPL is strongly expressed in mouse testis, with expression upregulated at puberty. The protein is expressed in human testis in a pattern similar to FKBP52 and also enhanced AR transcriptional activity in reporter assays. We examined sixty patients from the Japanese patient group and found one inactivating mutation and one coding change, as well as a number of non-coding changes, all absent in fifty-six controls. A second, Irish patient cohort of thirty showed another two coding changes not present in thirty proven fertile controls.

CONCLUSIONS

Our results describe the first alterations in the gene for FKBPL in azoospermic patients and indicate a potential role in AR-mediated signalling in the testis.

Mouse cumulus-denuded oocytes restore developmental capacity completely when matured with optimal supplementation of cysteamine, cystine, and cumulus cells

Our objectives were to study how cysteamine, cystine, and cumulus cells (CCs), as well as oocytes interact to increase oocyte intracellular glutathione (GSH) and thereby to establish an efficient in vitro maturation system for cumulus-denuded oocytes (DOs). Using M16 that contained no thiol as maturation medium, we showed that when supplemented alone, neither cystine nor cysteamine promoted GSH synthesis of mouse DOs, but they did when used together. Although goat CCs required either cysteamine or cystine to promote GSH synthesis, mouse CCs required both. In the presence of cystine, goat CCs produced cysteine but mouse CCs did not. Cysteamine reduced cystine to cysteine in cell-free M16. When TCM-199 that contained 83 microM cystine was used as maturation medium, supplementation with cysteamine alone had no effect, but supplementation with 100 microM cysteamine and 200 microM cystine increased blastulation of DOs matured with CC coculture to a level as high as achieved in cumulus-surrounded oocytes (COCs). Similar numbers of young were produced after two-cell embryos from mouse COCs or CC-cocultured DOs matured with optimal thiol supplementation were transferred to pseudopregnant recipients. It is concluded that 1) mouse CCs can use neither cysteamine nor cystine to promote GSH synthesis, but goat CCs can use either one; 2) goat CCs promote mouse oocyte GSH synthesis by reducing cystine to cysteine, but how they use cysteamine requires further investigation; and 3) mouse DOs can use neither cystine nor cysteamine for GSH synthesis, but they restore developmental capacity completely when matured in the presence of optimum supplementation of cysteamine, cystine, and CCs.

RFX2 is a candidate downstream amplifier of A-MYB regulation in mouse spermatogenesis

Background

Mammalian spermatogenesis involves formation of haploid cells from the male germline and then a complex morphological transformation to generate motile sperm. Focusing on meiotic prophase, some tissue-specific transcription factors are known (A-MYB) or suspected (RFX2) to play important roles in modulating gene expression in pachytene spermatocytes. The current work was initiated to identify both downstream and upstream regulatory connections for Rfx2.

Results

Searches of pachytene up-regulated genes identified high affinity RFX binding sites (X boxes) in promoter regions of several new genes: Adam5, Pdcl2, and Spag6. We confirmed a strong promoter-region X-box for Alf, a germ cell-specific variant of general transcription factor TFIIA. Using Alf as an example of a target gene, we showed that its promoter is stimulated by RFX2 in transfected cells and used ChIP analysis to show that the promoter is occupied by RFX2 in vivo. Turning to upstream regulation of the Rfx2 promoter, we identified a cluster of three binding sites (MBS) for the MYB family of transcription factors. Because testis is one of the few sites of A-myb expression, and because spermatogenesis arrests in pachytene in A-myb knockout mice, the MBS cluster implicates Rfx2 as an A-myb target. Electrophoretic gel-shift, ChIP, and co-transfection assays all support a role for these MYB sites in Rfx2 expression. Further, Rfx2 expression was virtually eliminated in A-myb knockout testes. Immunohistology on testis sections showed that A-MYB expression is up-regulated only after pachytene spermatocytes have clearly moved away from the tubule wall, which correlates with onset of RFX2 expression, whereas B-MYB expression, by contrast, is prevalent only in earlier spermatocytes and spermatogonia.

Conclusion

With an expanding list of likely target genes, RFX2 is potentially an important transcriptional regulator in pachytene spermatocytes. Rfx2 itself is a good candidate to be regulated by A-MYB, which is essential for meiotic progression. If Alf is a genuine RFX2 target, then A-myb, Rfx2, and Alf may form part of a transcriptional network that is vital for completion of meiosis and preparation for post-meiotic differentiation.

Organotypic cultures of prepubertal mouse testes: a method to study androgen action in sertoli cells while preserving their natural environment

Cluster analysis at Postnatal Day 8-20 of putative androgen-regulated genes in mice with Sertoli cell-selective knockout of the androgen receptor (SCARKO) has pinpointed three genes (Spinlw1, Gpd1, Drd4) with an expression pattern strongly resembling that of Rhox5, the definitive Sertoli cell (SC) androgen-regulated gene. We used organotypic testis cultures from Day 8 mice to study control of these genes by (anti)androgens and follicle-stimulating hormone (FSH). Testis morphology and androgen induction of the studied genes were preserved for 48 h. Preincubation with ketoconazole for 24 h to block endogenous androgen production, followed by 24-h incubation with the synthetic androgen R1881, resulted in 45-, 5-, 19-, and 6-fold induction of mRNA levels of Rhox5, Spinlw1, Gpd1, and Drd4, respectively. However, noticeable differences in control of the studied genes were observed. Rhox5 and Spinlw1 were fully induced by R1881 in the continuous (48 h) presence of ketoconazole, whereas only marginal effects were observed on expression of Gpd1 and Drd4. Similarly, FSH only marginally affected expression of Rhox5 and Spinlw1, whereas it markedly increased Gpd1 and Drd4 expression. Explant cultures of SCARKO testes confirmed the differential effects of FSH on the studied genes and, for Gpd1, showed that the effect did not depend on a functional androgen receptor in SC, whereas this was essential for the effects of FSH on Drd4. In conclusion, organotypic cultures represent the first in vitro approach to preserving androgen responsiveness of putative SC-expressed genes. This approach facilitates detailed analysis of their regulation in ways not possible in vivo.

Androgen action via testicular peritubular myoid cells is essential for male fertility

Androgens are essential for normal spermatogenesis and male fertility, but how androgens exert this effect remains uncertain. Androgen receptors (ARs) are expressed in several testicular cell types, but continuing uncertainty exists over which cell type mediates androgen control of spermatogenesis. Androgen signaling via Sertoli cells (SCs) is essential for complete spermatogenesis, but the role for androgen signaling via peritubular myoid (PTM) cells is contentious. To address this controversy, we generated PTM-specific AR-knockout (PTM-ARKO) mice in which gross reproductive development was normal, but all PTM-ARKO males were azoospermic and infertile. Testis weight was reduced beyond puberty, and in adulthood there was an 86% reduction in germ cells, compared with wild-type littermates. These changes were not explained by any deficits in testosterone, luteinizing hormone, or follicle-stimulating hormone concentrations. SC function was impaired in PTM-ARKO males, indicated by reduced seminiferous tubule fluid production and reduced expression of some androgen-dependent SC genes. Androgen action via PTM cells is therefore essential for normal testis function, spermatogenesis, and fertility in males. This study also provides the first direct evidence for the importance of androgen-driven stromal-epithelial interactions underpinning the regulation of spermatogenesis; PTM-ARKO mice will enable identification of the new molecular pathways involved.

Androgen-induced Rhox homeobox genes modulate the expression of AR-regulated genes

Rhox5, the founding member of the reproductive homeobox on the X chromosome (Rhox) gene cluster, encodes a homeodomain-containing transcription factor that is selectively expressed in Sertoli cells, where it promotes the survival of male germ cells. To identify Rhox5-regulated genes, we generated 15P-1 Sertoli cell clones expressing physiological levels of Rhox5 from a stably transfected expression vector. Microarray analysis identified many genes altered in expression in response to Rhox5, including those encoding proteins controlling cell cycle regulation, apoptosis, metabolism, and cell-cell interactions. Fifteen of these Rhox5-regulated genes were chosen for further analysis. Analysis of Rhox5-null male mice indicated that at least nine of these are Rhox5-regulated in the testes in vivo. Many of them have distinct postnatal expression patterns and are regulated by Rhox5 at different postnatal time points. Most of them are expressed in Sertoli cells, indicating that they are candidates to be directly regulated by Rhox5. Transfection analysis with expression vectors encoding different mouse and human Rhox family members revealed that the regulatory response of a subset of these Rhox5-regulated genes is both conserved and redundant. Given that Rhox5 depends on androgen receptor (AR) for expression in Sertoli cells, we examined whether some Rhox5-regulated genes are also regulated by AR. We provide several lines of evidence that this is the case, leading us to propose that RHOX5 serves as a key intermediate transcription factor that directs some of the actions of AR in the testes.

Transcriptional profiling of the hormone-responsive stages of spermatogenesis reveals cell-, stage-, and hormone-specific events

Spermatogenesis occurs within the highly complex seminiferous epithelium. This cyclic process is accompanied by dynamic stage-specific transcriptional changes and is driven by androgens and FSH by mechanisms that are unclear. Here we report the impact of acute androgen and FSH suppression on the transcriptional dynamics of the seminiferous epithelium. We used transcriptional profiling to compare the most hormone-sensitive seminiferous epithelial stages (VII and VIII) from control and hormone-suppressed adult rats, together with publicly available datasets to delineate stage- and cell-specific transcriptional changes. The analyses reveal that, in these stages, there was a hormone-responsive down-regulation of spermatogonial and Sertoli cell transcripts maximally expressed in the earlier spermatogenic stages (I-VI). Transcripts expressed in Sertoli cells from stage VII and beyond were both up- and down-regulated by hormone suppression, with lysosome function, immune system-related genes, and lipid metabolism predicted to be hormone responsive. Hormone-responsive genes with putative roles in integrin-mediated cell adhesion were also identified. In pachytene spermatocytes, there was an initiation of transcription likely important for the completion of meiosis. A transcriptional switch in round spermatids was observed, from a hormone-responsive down-regulation of transcripts expressed in steps 1-7 spermatids to a hormone-independent up-regulation of transcripts expressed in steps 8-11 and likely involved in spermatid differentiation and DNA compaction. This study points to the existence of hormone-responsive global transcriptional repressors in Sertoli cells, spermatogonia, and spermatids and reveals novel and diverse cell-specific responses of the seminiferous epithelium to hormone suppression.

Gonadotropin-regulated testicular RNA helicase (GRTH/DDX25): a multifunctional protein essential for spermatogenesis

Male germ cell maturation is governed by the expression of specific protein(s) in a precise temporal sequence during development. Gonadotropin-regulated testicular RNA helicase (GRTH/DDX25), a member of the Glu-Asp-Ala-Glu (DEAD)-box protein family, is a testis-specific gonadotropin/androgen-regulated RNA helicase that is present in germ cells (meiotic spermatocytes and round spermatids) and Leydig cells. GRTH is essential for completion of spermatogenesis as a posttranscriptional regulator of relevant genes during germ cell development. Male mice lacking GRTH are sterile with spermatogenic arrest due to failure of round spermatids to elongate, where striking structural changes and reduction in size of chromatoid bodies are observed. GRTH also plays a central role in preventing germ cell apoptosis. In addition to its inherent helicase unwinding/adenosine triphosphatase activities, GRTH binds to specific mRNAs as an integral component of ribonuclear protein particles. As a shuttle protein, GRTH transports target mRNAs from nucleus to the cytoplasm for storage in chromatoid bodies of spermatids, where they await translation during spermatogenesis. GRTH is also associated with polyribosomes to regulate target gene translation. The finding of a missense mutation associated with male infertility, where its expression associates with loss of GRTH phosphorylation, supports the relevance of GRTH to human germ cell development. We conclude that the mammalian GRTH/DDX25 is a multifunctional RNA helicase that is an essential regulator of spermatogenesis and is highly relevant for studies of male infertility and contraception.

Retinoblastoma protein plays multiple essential roles in the terminal differentiation of Sertoli cells

Retinoblastoma protein (RB) plays crucial roles in cell cycle control and cellular differentiation. Specifically, RB impairs the G(1) to S phase transition by acting as a repressor of the E2F family of transcriptional activators while also contributing towards terminal differentiation by modulating the activity of tissue-specific transcription factors. To examine the role of RB in Sertoli cells, the androgen-dependent somatic support cell of the testis, we created a Sertoli cell-specific conditional knockout of Rb. Initially, loss of RB has no gross effect on Sertoli cell function because the mice are fertile with normal testis weights at 6 wk of age. However, by 10-14 wk of age, mutant mice demonstrate severe Sertoli cell dysfunction and infertility. We show that mutant mature Sertoli cells continue cycling with defective regulation of multiple E2F1- and androgen-regulated genes and concurrent activation of apoptotic and p53-regulated genes. The most striking defects in mature Sertoli cell function are increased permeability of the blood-testis barrier, impaired tissue remodeling, and defective germ cell-Sertoli cell interactions. Our results demonstrate that RB is essential for proper terminal differentiation of Sertoli cells.

Sertoli cell androgen receptor DNA binding domain is essential for the completion of spermatogenesis

We examined the biological importance of Sertoli cell androgen receptor (AR) genomic interaction, using a Cre-loxP approach to selectively disrupt the AR DNA-binding domain (AR-DBD). Sertoli cell (SC)-specific transgenic Abpa or AMH promoters targeted Cre-mediated inframe excision of mouse Ar exon-3, encoding the AR-DBD second zinc-finger (ZF2), generating SC-specific mutant AR(DeltaZF2) lines designated Abp.SCAR(DeltaZF2) and AMH.SCAR(DeltaZF2), respectively. Both SCAR(DeltaZF2) lines produced infertile males exhibiting spermatogenic arrest, despite normal SC numbers and immunolocalized SC nuclear AR. Adult homozygous TgCre((+/+)) SCAR(DeltaZF2) or double-TgCre((+/-)) Abp/AMH.SCAR(DeltaZF2) males displayed equivalent small testes 30% of normal size, representing maximal Cre-loxP-disruption of Sertoli AR function. Hemizygous TgCre((+/-)) vs. homozygous TgCre((+/+)) Abp.SCAR(DeltaZF2) testes were larger (47% normal size) with more postmeiotic development, indicating dose-dependent Cre-mediated disruption of SC-specific AR-DBD activity. SCAR(DeltaZF2) males exhibited adult Leydig cell hypertrophy but normal serum testosterone levels. Sertoli cell-specific Rhox5 and Spinlw1 transcription, regulated by divergent or classical androgen-response elements, respectively, were both decreased in postnatal SCAR(DeltaZF2) vs. control testes, demonstrating SC-specific AR-DBD function as early as postnatal d 5. However, Rhox5 expression declined dose-dependently, whereas Spinlw1 expression increased, in adult TgCre((+/-)) and TgCre((+/+)) SCAR(DeltaZF2) testes, revealing differential temporal control for distinct AR-regulated transcripts. Androgen-repressed Ngfr was not up-regulated in SCAR(DeltaZF2) testes, suggesting maintenance of a nonclassical mechanism independent of AR-DBD. Thus, our unique SCAR(DeltaZF2) paradigm provided dose-dependent Cre-mediated disruption of testicular development and gene expression revealing that the AR-DBD is essential for SC function and postmeiotic spermatogenesis. Nongenomic or AR-DBD-independent pathways appear secondary or play no major independent role in SC function.