Follicle-stimulating hormone (FSH) regulates the expression of FSH receptor messenger ribonucleic acid in cultured Sertoli cells and in hypophysectomized rat testis

Revisiting the gonadotropic regulation of mammalian spermatogenesis: evolving lessons during the past decade

Spermatogenesis is a multi-step process of male germ cell (Gc) division and differentiation which occurs in the seminiferous tubules of the testes under the regulation of gonadotropins - Follicle Stimulating Hormone (FSH) and Luteinising hormone (LH). It is a highly coordinated event regulated by the surrounding somatic testicular cells such as the Sertoli cells (Sc), Leydig cells (Lc), and Peritubular myoid cells (PTc). FSH targets Sc and supports the expansion and differentiation of pre-meiotic Gc, whereas, LH operates via Lc to produce Testosterone (T), the testicular androgen. T acts on all somatic cells e.g.- Lc, PTc and Sc, and promotes the blood-testis barrier (BTB) formation, completion of Gc meiosis, and spermiation. Studies with hypophysectomised or chemically ablated animal models and hypogonadal (hpg) mice supplemented with gonadotropins to genetically manipulated mouse models have revealed the selective and synergistic role(s) of hormones in regulating male fertility. We here have briefly summarized the present concept of hormonal control of spermatogenesis in rodents and primates. We also have highlighted some of the key critical questions yet to be answered in the field of male reproductive health which might have potential implications for infertility and contraceptive research in the future.

Effects of follicle-stimulating hormone on fat metabolism and cognitive impairment in women during menopause

Lipid metabolism disorder is a common pathological manifestation of menopausal women, and is also an important risk factor for many diseases at this stage of life. Epidemiological studies have shown that high levels of follicle-stimulating hormone (FSH) in menopausal women are closely associated with changes in body composition, central obesity, and cognitive decline. Exogenous FSH causes growth and proliferation of adipose, whereas blockage of the FSH signaling pathway leads to decline in adipose. Mechanistically, FSH, FSH receptor (FSHR), G protein coupling, gene mutation and other pathways are involved in adipogenesis and cognitive impairment. Here, we review the critical role and potential interactions of FSH in adipogenesis and cognitive impairment in menopausal women. Further understanding of the exact mechanisms of FSH aggravating obesity and cognitive impairment may provide a new perspective for promoting healthy aging in menopausal women.

Characterization of gonadotropin receptors Fshr and Lhr in Japanese medaka, Oryzias latipes

Reproduction in vertebrates is controlled by the brain-pituitary-gonad axis, where the two gonadotropins follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) play vital parts by activating their cognate receptors in the gonads. The main purpose of this work was to study intra- and interspecies ligand promiscuity of teleost gonadotropin receptors, since teleost receptor specificity is unclear, in contrast to mammalian receptors. Receptor activation was investigated by transfecting COS-7 cells with either Fsh receptor (mdFshr, tiFshr) or Lh receptor (mdLhr, tiLhr), and tested for activation by recombinant homologous and heterologous ligands (mdFshβα, mdLhβα, tiFshβα, tiLhβα) from two representative fish orders, Japanese medaka (Oryzias latipes, Beloniformes) and Nile tilapia (Oreochromis niloticus, Cichliformes). Results showed that each gonadotropin preferentially activates its own cognate receptor. Cross-reactivity was detected to some extent as mdFshβα was able to activate the mdLhr, and mdLhβα the mdFshr. Medaka pituitary extract (MPE) stimulated CRE-LUC activity in COS-7 cells expressing mdlhr, but could not stimulate cells expressing mdfshr. Recombinant tiLhβα, tiFshβα and tilapia pituitary extract (TPE) could activate the mdLhr, suggesting cross-species reactivity for mdLhr. Cross-species reactivity was also detected for mdFshr due to activation by tiFshβα, tiLhβα, and TPE, as well as for tiFshr and tiLhr due to stimulation by mdFshβα, mdLhβα, and MPE. Tissue distribution analysis of gene expression revealed that medaka receptors, fshr and lhr, are highly expressed in both ovary and testis. High expression levels were found for lhr also in brain, while fshr was expressed at low levels. Both fshr and lhr mRNA levels increased significantly during testis development. Amino acid sequence alignment and three-dimensional modelling of ligands and receptors highlighted conserved beta sheet domains of both Fsh and Lh between Japanese medaka and Nile tilapia. It also showed a higher structural homology and similarity of transmembrane regions of Lhr between both species, in contrast to Fshr, possibly related to the substitution of the conserved cysteine residue in the transmembrane domain 6 in medaka Fshr with glycine. Taken together, this is the first characterization of medaka Fshr and Lhr using homologous ligands, enabling to better understand teleost hormone-receptor interactions and specificities. The data suggest partial ligand promiscuity and cross-species reactivity between gonadotropins and their receptors in medaka and tilapia.

Environmental polycyclic aromatic hydrocarbons mixture, in human blood levels, decreased oestradiol secretion by granulosa cells via ESR1 and GPER1 but not ESR2 receptor

Tissue-dependent oestrogenic and anti-oestrogenic activity of polycyclic aromatic hydrocarbons (PAHs) has been suggested. In this study, the effect of two PAH mixtures, M1 composed of all 16 priority pollutants and M2 composed of five (noted in the highest levels) compounds, on follicle-stimulating hormone receptor (FSHR) expression, basal or FSH-induced oestradiol (E2) secretion and aromatase cytochrome P450 (P450arom) protein expression, by non-luteinised human granulosa cell line (HGrC1) was determined. In addition, the consequences of gene silencing of oestrogen receptor alfa (siESR1), oestrogen receptor beta (siESR2) and a G protein-coupled receptor (siGPER1) on the above parameters were described. Neither PAH mixture had an effect on basal FSHR protein expression; however, both mixtures increased FSH-induced FSHR expression. Decreased E2 secretion and P450arom expression was also demonstrated. In both basal and FSH treated cells, siESR1 and siGPER1 reversed the inhibitory effect of the mixtures on E2 secretion; however, in siESR2 cells, the inhibitory effect was still observed. This study showed that both classic ESR1 and GPER1 were involved in the inhibitory effect of both PAH mixtures on E2 secretion and confirmed that expression of P450arom could be downregulated through the aryl hydrocarbon receptor and additionally through the ESR2.

Testosterone augments FSH signaling by upregulating the expression and activity of FSH-Receptor in Pubertal Primate Sertoli cells

The synergistic actions of Testosterone (T) and FSH via testicular Sertoli cells (Sc) regulate male fertility. We have previously reported that the actions of these hormones (T and FSH) in infant monkey testes are restricted only to the expansion of Sc and spermatogonial cells. The robust differentiation of male Germ cells (Gc) occurs after pubertal maturation of testis. The present study was aimed to investigate the molecular basis of the synergy between T and FSH action in pubertal primate (Macaca mulatta) Sc. Using primary Sc culture, we here have demonstrated that T (but not FSH) downregulated AMH and Inhibin-β-B (INHBB) mRNAs in pubertal Sc. We also found that, prolonged stimulation of T in pubertal Sc significantly elevated the expression of genes involved in FSH signaling pathway like FSH-Receptor (FSHR), GNAS and RIC8B, and this was associated with a rise in cAMP production. T also augmented FSH induced expression of genes like SCF, GDNF, ABP and Transferrin (TF) in pubertal Sc. We therefore conclude that T acts in synergy with FSH signaling in pubertal Sc. Such a coordinated network of hormonal signaling in Sc may facilitate the timely onset of the first spermatogenic wave in pubertal primates and is responsible for quantitatively and qualitatively normal spermatogenesis.

The expression of several reproductive hormone receptors can be modified by perfluorooctane sulfonate (PFOS) in adult male rats

This study was undertaken to evaluate the possible role of several reproductive hormone receptors on the disruption of the hypothalamic-pituitary-testis (HPT) axis activity induced by perfluorooctane sulfonate (PFOS). The studied receptors are the gonadotropin-releasing hormone receptor (GnRHr), luteinizing hormone receptor (LHr), follicle-stimulating hormone receptor (FSHr), and the androgen receptor (Ar). Adult male rats were orally treated with 1.0; 3.0 and 6.0 mg of PFOS kg(-1) d(-1) for 28 days. In general terms, PFOS can modify the relative gene and protein expressions of these receptors in several tissues of the reproductive axis. At the testicular level, apart from the expected inhibition of both gene and protein expressions of FSHr and Ar, PFOS also stimulates the GnRHr protein and the LHr gene expression. The receptors of the main hormones involved in the HPT axis may have an important role in the disruption exerted by PFOS on this axis.

The proteasome inhibitor bortezomib induces testicular toxicity by upregulation of oxidative stress, AMP-activated protein kinase (AMPK) activation and deregulation of germ cell development in adult murine testis

Understanding how chemotherapeutic agents mediate testicular toxicity is crucial in light of compelling evidence that male infertility, one of the severe late side effects of intensive cancer treatment, occurs more often than they are expected to. Previous study demonstrated that bortezomib (BTZ), a 26S proteasome inhibitor used to treat refractory multiple myeloma (MM), exerts deleterious impacts on spermatogenesis in pubertal mice via unknown mechanisms. Here, we showed that intermittent treatment with BTZ resulted in fertility impairment in adult mice, evidenced by testicular atrophy, desquamation of immature germ cells and reduced caudal sperm storage. These deleterious effects may originate from the elevated apoptosis in distinct germ cells during the acute phase and the subsequent disruption of Sertoli-germ cell anchoring junctions (AJs) during the late recovery. Mechanistically, balance between AMP-activated protein kinase (AMPK) activation and Akt/ERK pathway appeared to be indispensable for AJ integrity during the late testicular recovery. Of particular interest, the upregulated testicular apoptosis and the following disturbance of Sertoli-germ cell interaction may both stem from the excessive oxidative stress elicited by BTZ exposure. We also provided the in vitro evidence that AMPK-dependent mechanisms counteract follicle-stimulating hormone (FSH) proliferative effects in BTZ-exposed Sertoli cells. Collectively, BTZ appeared to efficiently prevent germ cells from normal development via multiple mechanisms in adult mice. Employment of antioxidants and/or AMPK inhibitor may represent an attractive strategy of fertility preservation in male MM patients exposed to conventional BTZ therapy and warrants further investigation.

Metformin inhibits follicle-stimulating hormone (FSH) action in human granulosa cells: relevance to polycystic ovary syndrome

BACKGROUND

Women with anovulatory polycystic ovary syndrome (PCOS) are generally insulin-resistant and as a consequence are often treated with the biguanide metformin. Results with metformin have, however, been variable with some studies demonstrating induction of regular cycles and an increase in ovulation, whereas others do not. Hence more understanding is needed regarding the mechanism of metformin's actions in ovarian granulosa cells especially in light of previous demonstrations of direct actions.

OBJECTIVE

The aim of this study was to investigate metformin's interaction with the FSH/cAMP/protein kinase A pathway, which is the primary signaling pathway controlling CYP19A1 (aromatase) expression in the ovary.

METHODS

The effect of metformin on FSH and forskolin-stimulated aromatase expression in human granulosa cells was measured by quantitative real-time PCR. Activity was assessed after transfection with a promoter II-luciferase construct, and by an RIA measuring conversion of androgen to estrogens. The effect on FSH receptor (FSHR) mRNA was assessed by quantitative PCR. Levels of phosphorylated cAMP response element binding protein (CREB) and CREB-regulated transcription coactivator 2 (CRTC2) were measured by Western blotting and cAMP by a bioluminescent assay.

RESULTS

Metformin markedly reduced FSH but not forskolin-stimulated aromatase expression and activity. This effect was exerted by inhibition of basal and ligand-induced up-regulation of FSHR expression. Metformin also reduced FSH-induced phosphorylation of CREB and hence CRE activity, which could potentially disrupt the CREB-CREB-binding protein-CRTC2 coactivator complex that binds to CRE in promoter II of the aromatase gene. This is mediated in an AMP-activated protein kinase-independent manner, and does not involve alteration of cAMP levels.

CONCLUSION

These finding have implications for the use of metformin in the treatment of anovulation in women with PCOS.

Impaired fertility and FSH synthesis in gonadotrope-specific Foxl2 knockout mice

Impairments in pituitary FSH synthesis or action cause infertility. However, causes of FSH dysregulation are poorly described, in part because of our incomplete understanding of mechanisms controlling FSH synthesis. Previously, we discovered a critical role for forkhead protein L2 (FOXL2) in activin-stimulated FSH β-subunit (Fshb) transcription in immortalized cells in vitro. Here, we tested the hypothesis that FOXL2 is required for FSH synthesis in vivo. Using a Cre/lox approach, we selectively ablated Foxl2 in murine anterior pituitary gonadotrope cells. Conditional knockout (cKO) mice developed overtly normally but were subfertile in adulthood. Testis size and spermatogenesis were significantly impaired in cKO males. cKO females exhibited reduced ovarian weight and ovulated fewer oocytes in natural estrous cycles compared with controls. In contrast, ovaries of juvenile cKO females showed normal responses to exogenous gonadotropin stimulation. Both male and female cKO mice were FSH deficient, secondary to diminished pituitary Fshb mRNA production. Basal and activin-stimulated Fshb expression was similarly impaired in Foxl2 depleted primary pituitary cultures. Collectively, these data definitively establish FOXL2 as the first identified gonadotrope-restricted transcription factor required for selective FSH synthesis in vivo.

Sertoli cell-specific expression of metastasis-associated protein 2 (MTA2) is required for transcriptional regulation of the follicle-stimulating hormone receptor (FSHR) gene during spermatogenesis

BACKGROUND

Desensitization of FSH response by down-regulation of FSHR transcription is critical for FSH action.

RESULTS

Chromatin modifier MTA2 participates in the down-regulation of FSHR transcription.

CONCLUSION

The FSH/Ar/MTA2 cascade may serve as an indispensable negative feedback mechanism to modulate FSH transduction events in Sertoli cells.

SIGNIFICANCE

Our findings provide new insights into mechanisms by which FSH is deregulated in male infertile patients. The effect of follicle-stimulating hormone (FSH) on spermatogenesis is modulated at a fundamental level by controlling the number of competent receptors present at the surface of Sertoli cells (SCs). One underlying mechanism is the down-regulation of the expression levels of the FSH receptor (FSHR) gene after exposure to FSH. Here we report that metastasis-associated protein 2 (MTA2), a component of histone deacetylase and nucleosome-remodeling complexes, as a gene product induced directly by testosterone or indirectly by FSH, is exclusively expressed in SCs. Stimulation of SCs with FSH is accompanied by up-regulation of MTA2 expression and enhancement of deacetylase activity. This effect requires the integrity of functional androgen receptor. Furthermore, MTA2 is a potent corepressor of FSHR transcription, because it can recruit histone deacetylase-1 onto the FSHR promoter and participates in the down-regulation of FSHR expression upon FSH treatment. Abolishment of endogenous MTA2 by siRNA treatment disrupted the desensitization of the FSH response and thereafter impaired the FSH-dependent secretory function of SCs. From a clinical standpoint, deregulated expression of MTA2 in SCs of human pathological testes negatively correlates to the deregulated level of serum FSH. Overall, our present results provide the first evidence that the FSH/androgen receptor/MTA2 cascade may serve as an indispensable negative feedback mechanism to modulate the transduction events of SCs in response to FSH. These data also underscore an unexpected reproductive facet of MTA2, which may operate as a novel integrator linking synergistic actions of FSH and androgen signaling in SCs.

A comprehensive curated resource for follicle stimulating hormone signaling

BACKGROUND

Follicle stimulating hormone (FSH) is an important hormone responsible for growth, maturation and function of the human reproductive system. FSH regulates the synthesis of steroid hormones such as estrogen and progesterone, proliferation and maturation of follicles in the ovary and spermatogenesis in the testes. FSH is a glycoprotein heterodimer that binds and acts through the FSH receptor, a G-protein coupled receptor. Although online pathway repositories provide information about G-protein coupled receptor mediated signal transduction, the signaling events initiated specifically by FSH are not cataloged in any public database in a detailed fashion.

FINDINGS

We performed comprehensive curation of the published literature to identify the components of FSH signaling pathway and the molecular interactions that occur upon FSH receptor activation. Our effort yielded 64 reactions comprising 35 enzyme-substrate reactions, 11 molecular association events, 11 activation events and 7 protein translocation events that occur in response to FSH receptor activation. We also cataloged 265 genes, which were differentially expressed upon FSH stimulation in normal human reproductive tissues.

CONCLUSIONS

We anticipate that the information provided in this resource will provide better insights into the physiological role of FSH in reproductive biology, its signaling mediators and aid in further research in this area. The curated FSH pathway data is freely available through NetPath (http://www.netpath.org), a pathway resource developed previously by our group.

Follicle-stimulating hormone (FSH) transiently blocks FSH receptor transcription by increasing inhibitor of deoxyribonucleic acid binding/differentiation-2 and decreasing upstream stimulatory factor expression in rat Sertoli cells

FSH acts through the FSH receptor (FSHR) to modulate cell processes that are required to support developing spermatozoa. Within the testis, only Sertoli cells possess receptors for FSH and are the major targets for this regulator of spermatogenesis. FSH stimulation of Sertoli cells for 24-48 h is known to induce Fshr mRNA expression through an E-box motif (CACGTG) located 25 bp upstream of the transcription start site. In contrast, FSH stimulation for 8 h inhibits Fshr transcription. DNA-protein binding studies performed using nuclear extracts from Sertoli cells show that protein binding to the Fshr promoter E-box was reduced 68% after 6 h of FSH stimulation but increased 191% over basal levels after 48 h of stimulation. The proteins binding to the Fshr E-box were identified as upstream stimulatory factor (USF)-1 and -2. FSH stimulation transiently decreased USF1 levels and increased the expression of the inhibitor of DNA binding/differentiation (ID)-2 repressor protein with the same kinetics as the decreased USF/E-box interactions. Overexpression of ID2 resulted in a dose-dependent decrease in USF-driven Fshr promoter activity in the MSC-1 Sertoli cell line, and ID2 inhibited USF binding to the Fshr E-box. Together, these studies suggest that stimulation of Sertoli cells with FSH transiently decreases expression of the USF1 activator and induces accumulation of the ID2 repressor, to block USF binding to the Fshr promoter and delay activation of Fshr transcription. This FSH-regulated mechanism may explain the cyclical changes in Fshr expression that occurs in Sertoli cells in vivo.

Fibroblasts from the new-born male testicle of Guangxi Bama mini-pig ( Sus scrofa) can support nuclear transferred embryo development in vitro

Miniature pigs are valuable for research in xenotransplantation and as models for investigating human diseases. Although many mammalian species have been cloned, the success rates have been very low, especially in the pig. In the present study, an attempt was made to optimize somatic cell nuclear transfer (SCNT) protocols for use in the production of the Guangxi Bama mini-pig. Firstly, mini-pig fibroblast cells from a new-born Guangxi Bama piglet were isolated and cultured. Cell type was identified by fluorescence immunocytochemistry (ICC); the cells expressed cimentin, but not cytoceratin and follicular stimulation hormone receptor (FSHR). Secondly, the optimal cell cycle synchronization protocol for treating fibroblast cells from the newborn piglet's testicle was investigated by contact inhibition and serum starvation. When fibroblast cells were treated by contact inhibition, a higher fusion (66.0% vs. 58.3%, p > 0.05) and blastocyst production (20.8% vs. 15.1, p > 0.05) rates were obtained than with serum starvation. Thirdly, to examine the ability of old cells to be morphologically remodelled after activation, testicular fibroblasts (passage 10-14) were introduced into enucleated oocytes; enlarged nuclei were formed in most of the reconstructed embryos at 6 h and enlarged nuclei or distinct pseudopronuclei were formed in nearly all the reconstructed embryos at 12 h. The old donor cell could be morphologically remodelled correctly and was competent to support embryo development to the blastocyst in vitro. Fourthly, the in vitro development potential of the cloned embryos was investigated using two types of donor cell: ear fibroblasts and low or high passage testicular fibroblasts. The rate of fusion was highest using low passage testicle fibroblasts (84.5% vs. 69.8% and 80.0%, p < 0.05), as was development to the blastocyst stage (14.6% vs. 7.7% and 6.3%, p < 0.05). Finally, the effect of phytohaemagglutinin (PHA) on parthenogenetic and cloned embryo development was examined. The PHA had no significant effect on the parthenogenetic embryos, but cloned embryo development to the blastocyst stage was significantly increased by PHA (10 microg/ml), (13.4% vs. 5.6% and 5.6%, p < 0.05).

Expression of gonadotropin and gonadotropin receptor genes during early sexual maturation in male Atlantic salmon parr

Atlantic salmon males may mature already as small parr in freshwater. Sexual maturation in teleosts as in vertebrates is characterized by the activation of the brain-pituitary-gonad axis. The endocrine regulation of early puberty is still not well understood. In the present study, one-summer-old male Atlantic salmon parr were sampled regularly from December several months prior to the beginning of spermatogenesis until spawning in October. Pituitary expression levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) beta subunit genes were analyzed in parallel with testis expression of FSH receptor (FSHR) and LH receptor (LHR) genes by RT-PCR and plasma 11-ketostestosterone (11-KT) was measured. Expression levels of FSHbeta, low during winter and spring started to increase prior to the onset of gonadal growth at the end of May while LHbeta mRNA levels were hardly detectable. Both gonadotropin receptor genes were expressed in immature testis with FSHR transcripts being more abundant (8-fold). FSHR transcript levels increased in parallel to FSHbeta levels from early spermatogenesis onwards, while LHR mRNA started to increase prior to any large changes in LHbeta expression. Both transcript levels of LHbeta and LHR were highest during spermiation. Plasma 11-KT increased at the beginning of spermatogenesis reaching highest levels at spermiogenesis suggesting a possible role of FSH in inducing 11-KT production during early spermatogenesis while LH stimulates via its specific receptor 11-KT production at spermiogenesis. The commitment into sexual maturation appears to be dependant on both the presence of FSHR in immature testis and the increase of FSH expression.

Role of gonadotropin and Leydig cell-secreted factors in the control of testicular macrophage activities in the wall lizard Hemidactylus flaviviridis

The present in vitro study for the first time demonstrates the endocrine and paracrine control of testicular macrophage activities in ectodermic vertebrates. Follicle-stimulating hormone (FSH) increased phagocytosis and superoxide production by macrophages. In regard to paracrine control, non-activated Leydig cell-conditioned medium (LCCM) decreased both the activities, whereas FSH-preactivated LCCM had differential effects: inhibitory on phagocytosis and stimulatory on superoxide production. However, FSH-activated LCCM, in addition to superoxide production, also enhanced phagocytosis. After heat inactivation, FSH-activated LCCM inhibited both the activities. Addition of FSH resulted in stimulation of phagocytosis, while partially restored the superoxide production. It can be speculated that androgen in heat-inactivated FSH-activated LCCM, in the presence of FSH, instead of inhibitory had stimulatory effect on phagocytosis, but remained inhibitory to superoxide production. Further, FSH-induced Leydig cell-secreted non-steroidal heat-labile factors appear to have stimulatory effect on superoxide production. This was corroborated by experiments with dihydrotestosterone in presence/absence of FSH.

FSH and testosterone signaling in Sertoli cells

Testosterone and follicle-stimulating hormone (FSH) are required to obtain full reproductive potential. In the testis, somatic Sertoli cells transduce signals from testosterone and FSH into the production of factors that are required by germ cells as they mature into spermatozoa. Recent advances in identifying new signaling pathways that are regulated by FSH and testosterone have allowed for refinement in the understanding of the independent, overlapping and synergistic actions of these hormones. In this review, we discuss the signaling pathways that are regulated by FSH and testosterone as well as the resulting metabolic and gene expression changes that occur as related to Sertoli cell proliferation, differentiation and the support of spermatogenesis.

Expression of androgen and estrogen receptors in sertoli cells: studies using the mouse SK11 cell line

Sertoli cells (Sc) play a major role in the establishment and maintenance of spermatogenesis. In the adult testis, Sc contain androgen receptor (AR) and estrogen receptor (ER)-beta but exhibit a loss of steroid responsiveness when maintained in primary culture. In the present study, we demonstrated that a transformed murine cell line (SK11) has retained a Sc phenotype and remains steroid responsive. SK11 cells expressed mRNAs found in Sc (aromatase, sulfated glycoprotein-1, sulfated glycoprotein-2, GATA-1, Sry-type high-mobility-group box transcription factor-9, testatin, dosage-sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene 1) including those for AR and ERbeta but not ERalpha. AR and ERbeta were immunolocalized to cell nuclei, and their ability to activate gene expression was investigated using transient transfections with reporter constructs containing either 3xERE or pem-androgen-responsive element promoters. Expression of the 3xERE reporter was induced after incubation with 17beta-estradiol (E2), 5alpha-androstane-3-beta, 17beta-diol (3betaAdiol), or testosterone (T); up-regulation of the pem-androgen-responsive element reporter was detected only in the presence of T or dihydrotestosterone. Activation of the ERE reporter did not occur after targeted knockdown of ERbeta mRNA. Expression of AR and ERbeta mRNAs was increased after incubation of cells with T or E2, respectively. In conclusion, we have demonstrated that the SK11 Sc cell line contains functional AR and ERbeta and that treatment of the cells with their respective steroids results in an increase in the amount of their mRNAs. Our results suggest that E2 or 3betaAdiol acting via ERbeta might modulate Sc function in vivo and that SK11 cells provide a useful model that can be used to complement studies using Sc selective gene ablation.

Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis

Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.

The Id2 transcriptional repressor is induced by follicle-stimulating hormone and cAMP

Id (inhibitor of DNA binding/differentiation) proteins repress differentiation and promote cell division by dimerizing with and inhibiting the action of basic helix-loop-helix transcription factors including those that bind to E-box motifs. Of the four characterized Id proteins, only Id2 is found in the nucleus of Sertoli cells that support the development of spermatozoa in the testis. Differential display analysis of rat primary Sertoli cell mRNA identified Id2 as being inducible by forskolin, a stimulator of cAMP production. Northern blot analysis confirmed that Id2 mRNA expression peaked in Sertoli cells 6-12 h after stimulation with forskolin or follicle-stimulating hormone (FSH), the major physiological stimulator of cAMP in Sertoli cells. Similarly, Id2 promoter activity in Sertoli cells was induced after forskolin or FSH stimulation as well as by overexpression of protein kinase A. Forskolin induction of the Id2 promoter required sequences located between positions -122 and -82. Protein(s) of 40-45 kDa were found to bind two activated transcription factor/cAMP-response element-like sites and a GATA motif within the regulatory region. The induction of the Id2 gene by FSH corresponded with a decrease in protein binding to an E-box consensus motif and decreased E-box-mediated transcription. Together, these findings raise the possibility that FSH-mediated induction of Id2 and resultant inhibition of basic helix-loop-helix transcription factor-regulated genes in Sertoli cells may contribute to the regulation of spermatogenesis.

Follicle-stimulating hormone increases testicular Anti-Mullerian hormone (AMH) production through sertoli cell proliferation and a nonclassical cyclic adenosine 5'-monophosphate-mediated activation of the AMH Gene

Anti-Müllerian hormone (AMH) production by testicular Sertoli cells is high before puberty and can be further induced by FSH. Our objective was to delineate the mechanisms by which FSH stimulates AMH production. Assay of serum AMH levels and histological morphometric analysis in prepubertal FSH-deficient transgenic mice showed that serum AMH and testicular mass were decreased owing to reduced Sertoli cell number. All parameters resumed normal values in mice treated with recombinant FSH. We also analyzed the ability of FSH and the factors involved in its signaling pathway to activate AMH transcription by transfecting AMH promoter-luc reporter constructs of different lengths in a prepubertal Sertoli cell line. Our results showed that FSH activates AMH transcription via adenylate cyclase, cAMP, and protein kinase A but involving a nonclassical cAMP-response pathway requiring nuclear factor-kappaB and activating protein 2 binding sites, which lie more than 1.9 kb upstream of the AMH transcription start site. This is the first report showing the importance of distant sequences in the regulation of AMH expression. We conclude that prepubertal testicular AMH production is increased by FSH stimulation through Sertoli cell proliferation and an enhancement of AMH gene transcription.

Molecular, structural, and cellular biology of follitropin and follitropin receptor

Follitropin and the follitropin receptor are essential for normal gamete development in males and females. This review discusses the molecular genetics and structural and cellular biology of the follitropin/follitropin receptor system. Emphasis is placed on the human molecules when possible. The structure and regulation of the genes for the follitropin beta subunit and the follitropin receptor is discussed. Control of systemic and cellular protein levels is explained. The structural biology of each protein is described, including protein structure, motifs, and activity relationships. Finally, the follitropin/follitropin receptor signal transduction system is discussed.

Basic properties and annual changes of follicle-stimulating hormone receptors in the testis of horseshoe bats, Rhinolophus ferrumequinum

The unique reproductive patterns, delayed fertilization in females, and asynchrony between spermatogenesis and mating behavior in males are well documented in bats living in temperate latitudes. The present study was undertaken to examine follicle-stimulating hormone (FSH) receptors in the testis of bats, Rhinolophus ferrumequinum, during the annual reproductive cycle. Male bats were captured at natural roosting sites and testicular preparations were subjected to a radioligand binding assay for FSH receptors. The weight of paired testes increased considerably in the spermatogenic period and decreased from the mating to hibernation periods. Meiotic division in the testis was observed in the spermatogenic period but not the mating period. Serum testosterone concentrations increased in the spermatogenic period and rapidly decreased in the mating period. The binding of FSH was specific for mammalian FSHs and detected primarily in the testis. Scatchard plot analyses of the binding of FSH to bat testicular preparations showed straight lines, suggesting the presence of a single class of binding sites. The affinities (equilibrium association constant) of FSH receptors were consistent throughout the annual reproductive cycle. The specific binding per unit weight of testis and total binding in the paired testes were highest in the mating period and in the spermatogenic period, respectively, among reproductive periods. The accumulation of cyclic adenosine 3', 5'-monophosphate to FSH stimulation was higher in the spermatogenic period than in the hibernation period. These findings suggest that testicular function of bats is associated with seasonal changes in the number of binding sites, while the number per target cell and the activation of adenylate cyclase led by FSH-receptor complex considerably decreases in the hibernation period.

The expression of the follicle-stimulating hormone receptor in spermatogenesis

Results from experiments using mouse models suggest that the role of follicle-stimulating hormone (FSH) in spermatogenesis is the regulation of Sertoli cell proliferation and, ultimately, the size and spermatogenic capacity of the testis. The regulation of the expression of the FSH receptor (FSHR) gene is very cell specific and plays an initial role in the ultimate response of the Sertoli cells to FSH. The extreme cell specificity and the importance of the FSH response to spermatogenesis have led to an extensive characterization of the promoter of the FSHR gene. Several widely expressed transcription factors - including USF 1 and 2, GATA-1, and SF-1 and potential elements such as an E2F site and an Inr region - have been shown to contribute to the maximal transcription of the transfected FSHR gene. However, these experiments have failed to provide clues as to the cell-specific expression of the FSHR gene. In both cell transfections and in transgenic mice, the promoter can direct expression of transgenes promiscuously. The rodent FSHR promoter contains conserved CpG dinucleotides that were shown to be methylated in nonexpressing cells and tissue but unmethylated in Sertoli cells. The methylated CpG sites could interfere with the binding of general transcription factors and/or lead to a repressive chromatin structure in the nonexpressing cells. While yet-undiscovered cell-specific factors may play a role in the expression of the FSHR gene, repression and activation of local chromatin structure are likely to be involved.

The functional significance of FSH in spermatogenesis and the control of its secretion in male primates

The aim of this review is to provide an integrative analysis of the role of FSH in the control of testicular function in higher primates, including man. Attention is focused on the action of FSH during neonatal development, puberty, and adulthood. Whether FSH is the major determinant of the adult complement of Sertoli cells and whether FSH is obligatory for the initiation, maintenance, and restoration of spermatogenesis is evaluated. The mechanism whereby the circulating concentration of FSH regulates spermatogonial proliferation to dictate the sperm production rate under physiological conditions in the adult is discussed in detail. Inhibin B is the major component of the testicular negative feedback signal governing FSH beta gene expression and FSH secretion, and the evidence for this view is presented. The review concludes with the presentation of a model for the operation of the FSH-inhibin B feedback control system regulating sperm production postpubertally in monkey and man, and with speculation on issues of clinical interest.

Activation of the rat follicle-stimulating hormone receptor promoter by steroidogenic factor 1 is blocked by protein kinase a and requires upstream stimulatory factor binding to a proximal E box element

The receptor for the pituitary glycoprotein hormone FSH (FSHR) and the nuclear hormone receptor steroidogenic factor 1 (SF-1) play important roles in control of the hypothalamic-pituitary- gonadal axis. FSHR is essential for integrating the pituitary FSH signal to gonadal response, while SF-1 is an important transcriptional regulator of many genes that function within this axis and is essential for the development of gonads and adrenal glands. Given the critical role of SF-1 in regulation of the gonads and the coexpression of FSHR and SF-1 in Sertoli and granulosa cells, we examined the ability of SF-1 to regulate transcription of the FSHR gene. We found that SF-1 stimulated rat FSHR promoter activity in a dose-dependent and promoter-specific manner. Examination of various promoter deletion mutants indicated that SF-1 acts through the proximal promoter region and upstream promoter sequences. An E box element within the proximal promoter is essential for activation of the FSHR promoter by SF-1. This element binds the transcriptional regulators USF1 and USF2 (upstream stimulatory factors 1 and 2) but not SF-1, as shown by electrophoretic mobility shift assays. In addition, functional studies identified a requirement for the USF proteins in SF-1 activation of FSHR and mapped an important regulatory domain within exons 4 and 5 of USF2. Cotransfection studies revealed that activation of protein kinase A leads to inhibition of SF-1-stimulated transcription of FSHR, while it synergized with SF-1 to activate the equine LH beta-promoter (ebeta). Thus, stimulation of the cAMP pathway differentially regulates SF-1 activation of the FSHR and ebeta-promoters.

Irradiation selectively inhibits expression from the androgen-dependent Pem homeobox gene promoter in sertoli cells

How radiation blocks spermatogenesis in certain strains of rats, such as LBNF(1), is not known. Because the block depends on androgen, we propose that androgen affects Sertoli cell function in irradiated LBNF(1) rats, resulting in the failure of spermatogonial differentiation. To begin to identify genes that may participate in this irradiation-induced blockade of spermatogenesis, we investigated the expression of several Sertoli genes in response to irradiation. The expression of the PEM: homeobox gene from its androgen-dependent Sertoli-specific proximal promoter (Pp) was dramatically reduced more than 100-fold in response to irradiation. In contrast, most other genes and gene products reported to be localized to the Sertoli cell, including FSH receptor (FSHR), androgen receptor (AR), SGP1, and the transcription factor CREB, did not exhibit significant changes in expression, whereas transferrin messenger RNA (mRNA) expression dramatically increased in response to irradiation. Irradiation also decreased Pp-driven PEM: mRNA levels in mouse testes (approximately 10-fold), although higher doses of irradiation than in rats were required to inhibit PEM: gene expression in testes of mice, consistent with their greater radioresistance. The decrease in Pem gene expression in mouse testis was also selective, as the expression of CREB, GATA-1, and SGP1 were little affected by irradiation. We conclude that the dramatic irradiation-triggered reduction of Pem expression in Sertoli cells is a conserved response that may be a marker for functional changes in response to irradiation.

Mechanisms involved in the homologous down-regulation of transcription of the follicle-stimulating hormone receptor gene in Sertoli cells

The action of follicle-stimulating hormone (FSH) in spermatogenesis is regulated at a fundamental level by controlling the number of competent receptors present at the surface of Sertoli cells. By controlling the number of receptors, the cell is able to modulate the timing and magnitude of subsequent signal transduction in response to FSH. One mechanism of control is the down-regulation of the steady state levels of the FSH receptor gene after exposure to FSH or agents that stimulate or prolong the cAMP signal transduction cascade (homologous down-regulation) in Sertoli cells. The goals of this study were to examine possible mechanisms involved in the down-regulation of mRNA levels of this gene. Analysis of transcription and processing by a PCR-based assay showed that treatment of Sertoli cells with FSH caused at least a 50% reduction of hnRNA for the FSH receptor gene. Reporter genes controlled by 5' flanking sequences of the FSH receptor gene that were transiently transfected into Sertoli cells were not down-regulated. In electrophoretic mobility shift assays (EMSA), cAMP-inducible nuclear protein complex containing c-Fos formed on the activator protein-1/cAMP responsive element-like site located at -216 to -210 in the promoter of the rat FSH receptor gene. We concluded from this study that there was no evidence for the putative role of ICER in the down-regulation of the FSH receptor promoter. In addition, the FSH-induced down-regulation of the transcription of the FSH receptor gene in Sertoli cells was prevented by the treatment of Sertoli cells with trichostatin A prior to the addition of FSH. This experiment coupled with other observations suggested that the down-regulation may be mediated by changes in chromatin structure.

Mutations of gonadotropins and gonadotropin receptors: elucidating the physiology and pathophysiology of pituitary-gonadal function

The recent unraveling of structures of genes for the gonadotropin subunits and gonadotropin receptors has provided reproductive endocrinologists with new tools to study normal and pathological functions of the hypothalamic-pituitary-gonadal axis. Rare inactivating mutations that produce distinctive phenotypes of isolated LH or FSH deficiency have been discovered in gonadotropin subunit genes. In addition, there is a common polymorphism in the LHbeta subunit gene with possible clinical significance as a contributing factor to pathologies of LH-dependent gonadal functions. Both activating and inactivating mutations have been detected in the gonadotropin receptor genes, a larger number in the LH receptor gene, but so far only a few in the gene for the FSH receptor. These mutations corroborate and extend our knowledge of clinical consequences of gonadotropin resistance and inappropriate gonadotropin action. The information obtained from human mutations has been complemented by animal models with disrupted or inappropriately activated gonadotropin ligand or receptor genes. These clinical and experimental genetic disease models form a powerful tool for exploring the physiology and pathophysiology of gonadotropin function and provide an excellent example of the power of molecular biological approaches in the study of pathogenesis of diseases.

Alteration of follicle-stimulating hormone and testosterone regulation of messenger ribonucleic acid for Sertoli cell proteins in the rat during the acute phase of spinal cord injury

The detrimental effects of spinal cord injury (SCI) on spermatogenesis in the rat can be attenuated by exogenous testosterone (T) but enhanced by exogenous follicle-stimulating hormone (FSH). These results suggest that T-dependent cellular events may be involved in testicular injury after SCI and that such events may be associated with modification of FSH effects on Sertoli cell function. The current study compared the responses of Sertoli cells to exogenous T and FSH after SCI or sham surgery using steady-state levels of Sertoli cell protein mRNA transcripts as markers of responsiveness. Rats underwent sham surgery or SCI and then were treated for 7 or 14 days with T-filled silastic capsules (2 x 5 cm) and/or daily injections of 0.1 units of porcine FSH. Vehicle-treated control rats received 5-cm empty capsules and daily injections of saline vehicle. Two weeks after sham surgery, levels of mRNA for the androgen receptor (AR), FSH receptor (FSHR), androgen-binding protein (ABP), or sulfated glycoprotein (SGP)-2 in the testis were unaffected by T or FSH alone. Testosterone alone, however, significantly decreased transferrin (Trf) mRNA levels in the testis (P: < 0.01). The combination of T and FSH treatments resulted in significant decreases in levels of the above transcripts (P: < 0.05; P: < 0.01). Seven days after SCI, the testes of vehicle-treated SCI rats had higher levels of AR and SGP-2 mRNA than did those of sham control rats (P: < 0.01); such effects were transient and disappeared by Day 14 post-SCI. Testosterone treatment of SCI rats for 7 days resulted in decreases in mRNA levels for AR and Trf in the testes (P: < 0.01) but increased testicular levels of mRNAs for FSHR and SGP-2 in SCI rats. Follicle-stimulating hormone treatment for 7 days prevented the increase in AR mRNA that was seen in the testis of untreated SCI rats and increased levels of ABP and SGP-2 mRNAs in SCI rats (P: < 0.01). Follicle-stimulating hormone treatment of SCI rats did not affect FSHR mRNA levels by itself, but it blocked the stimulatory effect of T on FSHR and SGP-2 mRNAs. Fourteen days after SCI, testicular AR mRNA levels were not affected by T alone, but they increased in those rats that received FSH with or without concurrent T treatments (P: < 0.05). In contrast to their effects in sham control rats, T or FSH alone or in combination resulted in significant increases in testicular levels of ABP, SGP-2, and FSHR mRNAs (P: < 0.05). At this time, Trf mRNA in the testis of SCI rats was also suppressed by T (P: < 0.05), as it did in sham control rats, but Trf mRNA was increased by the FSH (P: < 0.01) that had inhibited this transcript in the testes of sham control rats. The effects of FSH on the Sertoli cell transcripts in SCI rats were either attenuated or blocked when T was given concurrently. In addition, testicular and serum T levels in those SCI rats that received FSH (alone or in combination with T) for 14 days were significantly increased, an effect that was not seen after sham surgery. These findings demonstrate that hormonal regulation of both Sertoli and Leydig cells was altered during the acute phase of SCI. Such changes may modify the functions of both cell types, thereby affecting the endocrine and/or paracrine microenvironment within the seminiferous epithelium. These effects could impair the functional capacity of Sertoli cells and contribute to impairment of spermatogenesis after SCI.

Follicle-stimulating hormone inhibits all-trans-retinoic acid-induced retinoic acid receptor alpha nuclear localization and transcriptional activation in mouse Sertoli cell lines

The regulation of retinoic acid receptor alpha (RARalpha) signal transduction has not been well characterized. In this study, we determined whether all-trans-retinoic acid (tRA) and follicle-stimulating hormone (FSH) modulate RARalpha receptor subcellular localization, leading to changes in its transcriptional activity and protein expression in mouse Sertoli cell lines. We found that tRA induced the nuclear localization of RARalpha within 30 min and that longer term exposure increased the receptor transcriptional activity and RARalpha protein expression. Conversely, FSH suppressed the tRA-induced nuclear localization, transcriptional transactivation, and protein expression of RARalpha. Treatment with two different protein kinase A-selective antagonists reversed the inhibitory actions of FSH on tRA-dependent RARalpha nuclear localization and transcriptional activity. These results are consistent with the involvement of protein kinase A in mediating the inhibitory effects of FSH. For the first time, we demonstrate a unique signaling convergence between the RARalpha and the FSH-mediated signaling pathways, which may have significant implications in the testis because both are critical regulators of testis physiology.

Cloning and sequence analysis of the extracellular region of the polar bear (Ursus maritimus) luteinizing hormone receptor (LHr), follicle stimulating hormone receptor (FSHr), and prolactin receptor (PRLr) genes and their expression in the testis of the black bear (Ursus americanus)

Male black bears undergo seasonal changes in testicular activity. The testes are fully functional from May through July, regress from July through December, and recrudesce from January until May. The mechanisms responsible for the initiation of testicular recrudescence in the bear are unknown. The objectives of this study were to: (1) clone and sequence a substantial fragment of the extracellular portion of the luteinizing hormone receptor (LHr: 646 bp) and follicle stimulating hormone receptor (FSHr: 852 bp), and the extracellular/transmembrane portion of the prolactin receptor (PRLr: 680 bp) in the bear using reverse transcription-polymerase chain reaction (RT-PCR); and (2) determine whether the expression of LH-, FSH-, and PRL-receptor mRNA transcripts differs between the beginning and terminal stages of testicular recrudescence. Comparisons of the partial cDNA and predicted amino acid sequences of ursine receptors with the corresponding sequences from the pig, cow, human, and rat suggest that the LHr and FSHr are highly conserved (LHr: 87.1-93.7%; FSHr: 86.0-92.7%) whereas the PRLr is less well conserved (81-87%). Testicular LHr mRNA was more abundant during the breeding season in May than during the non-breeding season (early stage of recrudescence) in January. In contrast, testicular FSHr mRNA abundance was greater in January than in May. Testicular PRLr mRNA appeared equally abundant in January and May; however, two additional transcripts were present during the breeding season in May. This study provides molecular tools for future investigations of the control of testicular recrudescence in the black bear and demonstrates that the expression of testicular gonadotropin and PRL receptor mRNA is seasonally regulated. Mol. Reprod. Dev. 55:136-145, 2000.

The detrimental effects of spinal cord injury on spermatogenesis in the rat is partially reversed by testosterone, but enhanced by follicle-stimulating hormone

Our previous studies have demonstrated that impaired spermatogenesis during the acute phase of spinal cord injury (SCI) is preceded by a transient (but significant) suppression of serum FSH, LH, and testosterone (T) concentrations. It is hypothesized that hormonal deprivation may impair Sertoli cell function, leading to the loss of spermatogonia, degeneration of spermatogenic cells, and eventual regression of the seminiferous epithelium. The current study examined the efficacy of exogenous T and FSH in the maintenance of spermatogenesis and Sertoli cell functions in SCI rats. Implantation of T capsules (TC, 2 x 5 cm) attenuated some of the spermatogenic lesions and maintained qualitatively complete spermatogenesis in all SCI rats 4 weeks after the surgery. In contrast, daily injections of 0.1 U of FSH alone, or in combination with TC implants, paradoxically enhanced the regression of spermatogenesis in SCI rats. At this time, the numbers of Aal, A1, and B spermatogonia and preleptotene spermatocytes in SCI rats have decreased by 25-30%. Though not prevented by TC implants, the decrease in Aal and A1 spermatogonia was attenuated by FSH alone but was further enhanced when FSH-treated rats also received TC implants. The intratesticular T concentration in untreated and FSH-treated SCI rats was not different from that of sham control rats, but it decreased by more than 95% in those SCI rats given TC implants alone. These results demonstrate that impairment of spermatogenesis during the acute phase of SCI is not related to the availability of FSH and/or T. Northern blot analysis revealed an increase in androgen receptor messenger RNA (mRNA) in the testis of SCI rats; this increase was prevented by TC implants but persisted when FSH was also given. In contrast, the levels of FSH-receptor, androgen binding protein, and transferrin mRNA were not affected by SCI but were significantly higher in those SCI rats given FSH alone or in combination with TC. TC implants alone suppressed mRNA levels of transferrin in testes of SCI rats, without concomitant change in those for FSH-receptor and ABP. The changes in Sertoli cell responses to FSH and T, and perhaps other hormones, may alter signal events elicited by these hormones, thus contributing to abnormal epithelial environments and regression of spermatogenesis. Maintenance of spermatogenesis in SCI rats by exogenous T suggests the feasibility of using exogenous hormones to impede the detrimental effects of SCI on spermatogenesis. This approach may have clinical applicability for the preservation of spermatogenic functions in SCI men.

Effects of spinal cord injury on spermatogenesis and the expression of messenger ribonucleic acid for Sertoli cell proteins in rat Sertoli cell-enriched testes

The study was an examination of the effects of spinal cord injury (SCI) on spermatogenesis and Sertoli cell functions in adult rats with Sertoli cell-enriched (SCE) testes. The effects of SCI on the seminiferous epithelium were characterized by abnormalities in the remaining spermatogenic cells during the first month after SCI. Three days after SCI, serum testosterone levels were 80% lower, while serum FSH and LH levels were 25% and 50% higher, respectively, than those of sham control SCE rats. At this time, the levels of mRNA for androgen receptor (AR), FSH receptor (FSH-R), and androgen-binding protein (ABP) were normal whereas those for transferrin (Trf) had decreased by 40%. Thereafter, serum testosterone levels increased, but they remained lower than those of the sham control rats 28 days after SCI; and serum FSH and LH levels returned to normal. The levels of mRNA for AR, ABP, and Trf exhibited a biphasic increase 7 days after SCI and remained elevated 28 days after SCI. FSH-R mRNA levels were also elevated 90 days after SCI. Unexpectedly, active spermatogenesis, including qualitatively complete spermatogenesis, persisted in > 40% of the tubules 90 days after SCI. These results suggest that the stem cells and/or undifferentiated spermatogonia in SCE testes are less susceptible to the deleterious effects of SCI than the normal testes and that they were able to proliferate and differentiate after SCI. The presence of elevated levels of mRNA for Sertoli cell FSH-R and AR, as well as of that for the Sertoli cell proteins, in the SCE testes during the chronic stage of SCI suggests a modification of Sertoli cell physiology. Such changes in Sertoli cell functions may provide a beneficial environment for the proliferation of the stem cells and differentiation of postmeiotic cells, thus resulting in the persistence of spermatogenesis in these testes.

DEFT, a novel death effector domain-containing molecule predominantly expressed in testicular germ cells

Apoptosis is a physiological process by which multicellular organisms eliminate unwanted cells. Death factors such as Fas ligand induce apoptosis by triggering a series of intracellular protein-protein interactions mediated by defined motifs found in the signaling molecules. One of these motifs is the death effector domain (DED), a stretch of about 80 amino acids that is shared by adaptors, regulators, and executors of the death factor pathway. We have identified the human and rat complementary DNAs encoding a novel protein termed DEFT (Death EFfector domain-containing Testicular molecule). The N-terminus of DEFT shows a high degree of homology to the DEDs found in FADD (an adaptor molecule) as well as procaspase-8/FLICE and procaspase-10/Mch4 (executors of the death program). Northern blot hybridization experiments have shown that the DEFT messenger RNA (mRNA) is expressed in a variety of human and rat tissues, with particularly abundant expression in the testis. In situ hybridization analysis further indicated the expression of DEFT mRNA in meiotic male germ cells. In a model of germ cell apoptosis induction, an increase in testis DEFT mRNA was found in immature rats after 2 days of treatment with a GnRH antagonist. Unlike FADD and procaspase-8/FLICE, overexpression of DEFT did not induce apoptosis in Chinese hamster ovary cells. Although cotransfection studies indicated that DEFT is incapable of modulating apoptosis effected by FADD and procaspase-8/FLICE, interactions between DEFT and uncharacterized DED-containing molecules in the testis remain to be studied in the future. In conclusion, we have identified a novel DED-containing protein with high expression in testis germ cells. This protein may be important in the regulation of death factor-induced apoptosis in the testis and other tissues.