Molecular cloning of the mouse follicle-stimulating hormone receptor complementary deoxyribonucleic acid: functional expression of alternatively spliced variants and receptor inactivation by a C566T transition in exon 7 of the coding sequence

Long-read single-cell sequencing reveals the transcriptional landscape of spermatogenesis in obstructive azoospermia and Sertoli cell-only patients

BACKGROUND

High-throughput single-cell RNA sequencing (scRNA-seq) is widely used in spermatogenesis. However, it only reveals short reads in germ and somatic cells, limiting the discovery of novel transcripts and genes.

AIM

This study shows the long-read transcriptional landscape of spermatogenesis in obstructive azoospermia (OA) and Sertoli cell-only patients.

DESIGN

Single cells were isolated from testicular biopsies of OA and non-obstructive azoospermia (NOA) patients. Cell culture was identified by comparing PacBio long-read single-cell sequencing (OA n = 3, NOA n = 3) with short-read scRNA-seq (OA n = 6, NOA n = 6). Ten germ cell types and eight somatic cell types were classified based on known markers.

METHODS

PacBio long-read single-cell sequencing, short-read scRNA-seq, polymerase chain reaction.

RESULTS

A total of 130 426 long-read transcripts (100 517 novel transcripts and 29 909 known transcripts) and 49 508 long-read transcripts (26 002 novel transcripts and 23 506 known transcripts) have been detected in OA and NOA patients, respectively. Moreover, 36 373 and 1642 new genes are identified in OA and NOA patients, respectively. Importantly, specific expressions of long-read transcripts were detected in germ and stomatic cells during normal spermatogenesis.

CONCLUSION

We have identified total full-length transcripts in OA and NOA, and new genes were found. Furthermore, specific expressed full-length transcripts were detected, and the genomic structure of transcripts was mapped in different cell types. These findings may provide valuable information on human spermatogenesis and the treatment of male infertility.

Transcriptomic analysis of testis and epididymis tissues from Banna mini-pig inbred line boars with single-molecule long-read sequencing†

In mammals, testis and epididymis are critical components of the male reproductive system for androgen production, spermatogenesis, sperm transportation, as well as sperm maturation. Here, we report single-molecule real-time sequencing data from the testis and epididymis of the Banna mini-pig inbred line (BMI), a promising laboratory animal for medical research. We obtained high-quality full-length transcriptomes and identified 9879 isoforms and 8761 isoforms in the BMI testis and epididymis, respectively. Most of the isoforms we identified have novel exon structures that will greatly improve the annotation of testis- and epididymis-expressed genes in pigs. We also found that 3055 genes (over 50%) were shared between BMI testis and epididymis, indicating widespread expression profiles of genes related to reproduction. We characterized extensive alternative splicing events in BMI testis and epididymis and showed that 96 testis-expressed genes and 79 epididymis-expressed genes have more than six isoforms, revealing the complexity of alternative splicing. We accurately defined the transcribed isoforms in BMI testis and epididymis by combining Pacific Biotechnology Isoform-sequencing (PacBio Iso-Seq) and Illumina RNA Sequencing (RNA-seq) techniques. The refined annotation of some key genes governing male reproduction will facilitate further understanding of the molecular mechanisms underlying BMI male sterility. In addition, the high-confident identification of 548 and 669 long noncoding RNAs (lncRNAs) in these two tissues has established a candidate gene set for future functional investigations. Overall, our study provides new insights into the role of the testis and epididymis during BMI reproduction, paving the path for further studies on BMI male infertility.

Upsurge in autophagy, associated with mifepristone-treated polycystic ovarian condition, is reversed upon thymoquinone treatment

Polycystic ovarian syndrome (PCOS) is a multi-factorial gynecological endocrine disorder. It affects fertility in women and also predisposes to insulin resistance, type 2 diabetes mellitus, obesity etc. Earlier, significance of autophagy has been explored in PCOS-related metabolic disorders and during normal folliculogenesis. Increasing evidences reveal connection of autophagy with chronic inflammatory behaviour, an associated phenomena in polycystic ovaries. However, understanding of the association of autophagy with PCOS is still obscure. This study reveals that increased autophagy in mifepristone (RU486) treated KK-1 cells and in vivo PCO rat model is characterized by upregulated Androgen Receptor (AR) expression and downregulated PCO biomarker aromatase. The prevalence of autophagy has been observed to be concomitant with increased expression of two autophagic markers Beclin1 and MAP-LC3-II while the autophagy substrate p62/SQSTM1 was downregulated. Immunohistochemical staining revealed increased localization of MAP-LC3 in the compacted granulosa layers of the follicular cysts in the PCO model. The PCO rat models also demonstrated augmented levels of p65, the active subunit of NF-κB, which acts as a transcriptional regulator of several pro-inflammatory factors. NF-κB repressor and anti-inflammatory herbal drug thymoquinone, known to alleviate PCO condition, downregulated autophagy modules substantially. Pre-treatment with thymoquinone upregulated aromatase, reduced AR levels and decreased autophagic markers as well as p65 levels, simulating super-ovulated condition. In conclusion, the anti-inflammatory phytochemical thymoquinone alleviated PCO condition.

The Function of Pre-mRNA Alternative Splicing in Mammal Spermatogenesis

Alternative pre-mRNA splicing plays important roles in co-transcriptional and post-transcriptional regulation of gene expression functioned during many developmental processes, such as spermatogenesis. The studies focusing on alternative splicing on spermatogenesis supported the notion that the development of testis is regulated by a higher level of alternative splicing than other tissues. Here, we aim to review the mechanisms underlying alternative splicing, particularly the splicing variants functioned in the process of spermatogenesis and the male infertility. There are five points regarding the alternative splicing including ⅰ) a brief introduction of alternative pre-mRNA splicing; ⅱ) the alternative splicing events in spermatogenesis-associated genes enriched in different stages of spermatogenesis; ⅲ) the mechanisms of alternative splicing regulation, such as splicing factors and m⁶A demethylation; ⅳ) the splice site recognition and alternative splicing, including the production and degradation of abnormal transcripts caused by gene variations and nonsense-mediated mRNA decay, respectively; ⅴ) abnormal alternative splicing correlated with male infertility. Taking together, this review highlights the impacts of alternative splicing and splicing variants in mammal spermatogenesis and provides new insights of the potential application of the alternative splicing into the therapy of male infertility.

Expression and localization of follicle-stimulating hormone receptor in the yak uterus during different stages of the oestrous cycle

Morphological changes of the uterus and alterations in its secretory activity under the influence of steroid hormones been well documented. The oestrous cycle is also associated with significant changes in plasma follicle-stimulating hormone (FSH), whose effects are mediated through its receptor (FSHR). Reports showed that in many mammals, FSHR was expressed in gonadal and extragonadal tissues including cervix, female reproductive tract, and pituitary gland. Follicle-stimulating hormone (FSH) signals through endothelial FSHR directly stimulate angiogenesis and involved in the timing of birth in human, and the presence of FSHR in the placenta is essential for normal pregnancy in mice. But little is known about FSHR expression in the yak uterus. The main objective of the present study was to determine the expression and localization of FSHR in the yak uterus during different phases of the oestrous cycle. Results showed that FSHR protein was localized in the surface and glandular epithelial cells, stroma cells, myometrial smooth muscle cells and blood vessel endothelial cells. The expression of FSHR protein peaked at oestrus, significantly decreased at dioestrus (p < 0.05) and increased again at proestrus. FSHR mRNA was highly expressed at both proestrus and oestrus, and decreased at metestrus with the lowest values at dioestrus (p < 0.05). In conclusion, FSHR expression in the yak uterus changed with the stage of the oestrous cycle suggesting that FSHR plays an essential role in regulating the endometrial and myometrial functions during the oestrus cycle in the yak.

Molecular characterization, expression profile of the FSHRgene and its association with egg production traits in muscovy duck

Follicle-stimulating hormone (FSH) and its receptor play a key role in the follicular development and regulation of steroidogenesis in the ovary and spermatogenesis in the testis. The purpose of this study was to characterize themuscovy duck FSHR gene, identify SNPs and their association with egg production traits in muscovy ducks. Here, we cloned the complementary DNA (cDNA) sequence of FSHR, and examined the expression patterns of FSHR gene in adult female muscovy duck tissues. The cloned cDNA of the muscovy duck FSHR gene shared high similarity to those of pekin duck (Anas platyrhynchos) (95.7%) and chicken (93.2%). Three different muscovy duck FSHR transcripts were identified. Quantitative real-time PCR (RT-qPCR) results showed that the FSHR gene was expressed in all the 14 tested tissues, and the highest expression level was seen in the ovary. A total of 16 SNPs were identified, among which, four SNPs were located in the coding region of FSHR. The SNP C320T is significantly associated with egg production at 59 weeks of age (P < 0.05), whereas the SNP A227G is significantly associated with age at first egg stage (P < 0.05). These results suggest that the two SNPs (A227G and C320T) of FSHR gene are associated with egg production traits and could be potential markers that can be used for marker-assisted selection programmes to increase egg production in muscovy duck.

The Follitropin Receptor: Matching Structure and Function

Follitropin, or follicle-stimulating hormone (FSH) receptor (FSHR), is a G protein-coupled receptor belonging to the glycoprotein hormone receptor family that plays an essential role in reproduction. Although its primary location is the gonad, the FSHR has also been reported in extragonadal tissues including bone, placenta, endometrium, liver, and blood vessels from a number of malignant tumors. The recently resolved crystal structure of FSH bound to the entire FSHR ectodomain has been instrumental in more clearly defining the role of this domain in ligand binding and receptor activation. Biochemical, biophysical, and structural data also indicate that the FSHR exists as a higher order structure and that it may heterodimerize with its closely related receptor, the luteinizing hormone receptor; this association may have physiologic implications during ovarian follicle maturation given that both receptors may simultaneously coexist in the same cell. FSHR heterodimerization is unique to the ovary because in the testes, gonadotropin receptors are expressed in separate compartments. FSHR self-association appears to be required for receptor coupling to multiple effectors and adaptors, for the activation of multiple signaling pathways and the transduction of asymmetric signaling, and for negative and positive receptor cooperativity. It also provides a mechanism through which the glycosylation variants of FSH may exert distinct and differential effects at the target cell level. Given its importance in regulating activation of distinct signaling pathways, functional selectivity at the FSHR is briefly discussed, as well as the potential implications of this particular functional feature on the design of new pharmacological therapies in reproduction.

Follicle-Stimulating Hormone Receptor as a Target in the Redirected T-cell Therapy for Cancer

Adoptive transfer of T cells engineered to express chimeric immunoreceptors is an effective strategy to treat hematologic cancers; however, the use of this type of therapy for solid cancers, such as ovarian cancer, remains challenging because a safe and effective immunotherapeutic target has not yet been identified. Here, we constructed and evaluated a novel redirected T-cell-based immunotherapy targeting human follicle-stimulating hormone receptor (FSHR), a highly conserved molecule in vertebrate animals with expression limited to gonadal tissues, ovarian cancer, and cancer-associated vasculature. Receptor ligand-based anti-FSHR immunoreceptors were constructed that contained small binding fragments from the ligand for FSHR, FSH, fused to T-cell transmembrane and T-cell signaling domains. Human T cells transduced to express anti-FSHR immunoreceptors were specifically immunoreactive against FSHR-expressing human and mouse ovarian cancer cell lines in an MHC-nonrestricted manner and mediated effective lysis of FHSR-expressing tumor cells, but not FSHR-deficient targets, in vitro. Similarly, the outgrowth of human ovarian cancer xenografts in immunodeficient mice was significantly inhibited by the adoptive transfer of FSHR-redirected T cells. Our experimental observations show that FSHR is a promising immunotherapeutic target for ovarian cancer and support further exploration of FSHR-targeted immune therapy approaches for patients with cancer.

Follicle-stimulating hormone receptor (FSHR) alternative skipping of exon 2 or 3 affects ovarian response to FSH

Genes critical for fertility are highly conserved in mammals. Interspecies DNA sequence variation, resulting in amino acid substitutions and post-transcriptional modifications, including alternative splicing, are a result of evolution and speciation. The mammalian follicle-stimulating hormone receptor (FSHR) gene encodes distinct species-specific forms by alternative splicing. Skipping of exon 2 of the human FSHR was reported in women of North American origin and correlated with low response to ovarian stimulation with exogenous follicle-stimulating hormone (FSH). To determine whether this variant correlated with low response in women of different genetic backgrounds, we performed a blinded retrospective observational study in a Turkish cohort. Ovarian response was determined as low, intermediate or high according to retrieved oocyte numbers after classifying patients in four age groups (<35, 35-37, 38-40, >40). Cumulus cells collected from 96 women undergoing IVF/ICSI following controlled ovarian hyperstimulation revealed four alternatively spliced FSHR products in seven patients (8%): exon 2 deletion in four patients; exon 3 and exons 2 + 3 deletion in one patient each, and a retention of an intron 1 fragment in one patient. In all others (92%) splicing was intact. Alternative skipping of exons 2, 3 or 2 + 3 were exclusive to low responders and was independent of the use of agonist or antagonist. Interestingly, skipping of exon 3 occurs naturally in the ovaries of domestic cats--a good comparative model for human fertility. We tested the signaling potential of human and cat variants after transfection in HEK293 cells and FSH stimulation. None of the splicing variants initiated cAMP signaling despite high FSH doses, unlike full-length proteins. These data substantiate the occurrence of FSHR exon skipping in a subgroup of low responders and suggest that species-specific regulation of FSHR splicing plays diverse roles in mammalian ovarian function.

Relaxin family peptides and their receptors

There are seven relaxin family peptides that are all structurally related to insulin. Relaxin has many roles in female and male reproduction, as a neuropeptide in the central nervous system, as a vasodilator and cardiac stimulant in the cardiovascular system, and as an antifibrotic agent. Insulin-like peptide-3 (INSL3) has clearly defined specialist roles in male and female reproduction, relaxin-3 is primarily a neuropeptide involved in stress and metabolic control, and INSL5 is widely distributed particularly in the gastrointestinal tract. Although they are structurally related to insulin, the relaxin family peptides produce their physiological effects by activating a group of four G protein-coupled receptors (GPCRs), relaxin family peptide receptors 1-4 (RXFP1-4). Relaxin and INSL3 are the cognate ligands for RXFP1 and RXFP2, respectively, that are leucine-rich repeat containing GPCRs. RXFP1 activates a wide spectrum of signaling pathways to generate second messengers that include cAMP and nitric oxide, whereas RXFP2 activates a subset of these pathways. Relaxin-3 and INSL5 are the cognate ligands for RXFP3 and RXFP4 that are closely related to small peptide receptors that when activated inhibit cAMP production and activate MAP kinases. Although there are still many unanswered questions regarding the mode of action of relaxin family peptides, it is clear that they have important physiological roles that could be exploited for therapeutic benefit.

The molecular basis of impaired follicle-stimulating hormone action: evidence from human mutations and mouse models

The pituitary gonadotropin follicle-stimulating hormone (FSH) interacts with its membrane-bound receptor to produce biologic effects. Traditional functions of FSH include follicular development and estradiol production in females, and the regulation of Sertoli cell action and spermatogenesis in males. Knockout mice for both the ligand (Fshb) and the receptor (Fshr) serve as models for FSH deficiency, while Fshb and Fshr transgenic mice manifest FSH excess. In addition, inactivating mutations of both human orthologs (FSHB and FSHR) have been characterized in a small number of patients, with phenotypic effects of the ligand disruption being more profound than those of its receptor. Activating human FSHR mutants have also been described in both sexes, leading to a phenotype of normal testis function (male) or spontaneous ovarian hyperstimulation syndrome (females). As determined from human and mouse models, FSH is essential for normal puberty and fertility in females, particularly for ovarian follicular development beyond the antral stage. In males, FSH is necessary for normal spermatogenesis, but there are differences in human and mouse models. The FSHB mutations in humans result in azoospermia; while FSHR mutations in humans and knockouts of both the ligand and the receptor in mice affect testicular function but do not result in absolute infertility. Available evidence also indicates that FSH may also be necessary for normal androgen synthesis in males and females.

Absence of seasonal changes in FSHR gene expression in the cat cumulus-oocyte complex in vivo and in vitro

Domestic cat oocytes are seasonally sensitive to FSH. Compared with those collected during the breeding season, oocytes from the nonbreeding (NB) season require more FSH during in vitro maturation to achieve comparable developmental competence. This study tested the hypothesis that this seasonal variation was due to altered expression of FSH receptors (FSHR) and/or FSH-induced genes. Relative expression levels of FSHR mRNA and FSH-enhanced gene estrogen receptor β (ESR2) were measured by qPCR in whole ovaries and immature cumulus-oocyte complexes (COCs) isolated from cat ovaries during the natural breeding vs NB seasons. Expression levels of FSH-induced genes prostaglandin-endoperoxide synthase 2 (PTGS2), early growth response protein-1 (EGR1), and epidermal growth factor receptor (EGFR) were examined in mature COCs from both seasons that were a) recovered in vivo or b) matured in vitro with conventional (1 μg/ml) or high (10 μg/ml) FSH concentrations. Overall, FSHR mRNA levels were lower in whole ovaries during the NB compared with breeding season but were similar in immature COCs, whereas ESR2 levels did not differ in either group between intervals. We observed changes in PTGS2, EGR1, and EGFR mRNA expression patterns across maturation in COCs within but not between the two seasons. The lack of seasonal differentiation in FSH-related genes was not consistent with the decreased developmental capacity of oocytes fertilized during the NB season. These findings reveal that the seasonal decrease in cat oocyte sensitivity to FSH occurs both in vivo and in vitro. Furthermore, this decline is unrelated to changes in expression of FSHR mRNA or mRNA of FSH-induced genes in COCs from antral follicles.

Current concepts of follicle-stimulating hormone receptor gene regulation

Follicle-stimulating hormone (FSH), a pituitary glycoprotein hormone, is an integral component of the endocrine axis that regulates gonadal function and fertility. To transmit its signal, FSH must bind to its receptor (FSHR) located on Sertoli cells of the testis and granulosa cells of the ovary. Thus, both the magnitude and the target of hormone response are controlled by mechanisms that determine FSHR levels and cell-specific expression, which are supported by transcription of its gene. The present review examines the status of FSHR/Fshr gene regulation, emphasizing the importance of distal sequences in FSHR/Fshr transcription, new insights gained from the influx of genomics data and bioinformatics, and emerging trends that offer direction in deciphering the FSHR/Fshr regulatory landscape.

Single-nucleotide polymorphisms in the FSH receptor gene and ovarian performance: future role in IVF

The ovarian response to follicle stimulating hormone (FSH) stimulation in assisted conception cycles is variable. Although it would be beneficial to predict accurately the response of patients to FSH, to date no absolute predictors of ovarian performance have been identified. Recently, there have been a number of studies on the effect of single-nucleotide polymorphisms (SNPs) in the FSH receptor gene and its predictability in ovarian response to FSH stimulation. Several reports have shown that two very common SNPs at positions 307 and 680 in exon 10 of the FSH receptor gene are associated with ovarian response in IVF. The SNPs in exon 10 result in four discrete allelic variants characterised by the amino acid combinations Thr(307)-Asn(680), Ala(307)-Ser(680), Ala(307)-Asn(680) and Thr(307)-Ser(680). Because Thr(307) is almost always in linkage disequilibrium with Asn(680), and Ala(307) almost always with Ser(680), most studies are focussed solely on position 680. Some authors have shown predictability of ovarian response to FSH stimulation in patients with different alleles, while others have refuted this finding. In vitro models have not shown any difference in response among various alleles. Most of the available studies are retrospective, observational. Until now, there is no clear clinical benefit in the screening for SNP before IVF treatment. However, there is the prospect of devising mathematical models using a group of polymorphisms to provide an important tool for improving ovulation induction, especially in poor responders.

Female mice expressing constitutively active mutants of FSH receptor present with a phenotype of premature follicle depletion and estrogen excess

Strong gain-of-function mutations have not been identified in humans in the FSH receptor (FSHR), whereas such mutations are common among many other G protein-coupled receptors. In order to predict consequences of such mutations on humans, we first identified constitutively activated mutants of the mouse (m) Fshr and then expressed them under the human anti-Müllerian hormone promoter in transgenic mice or created knock-in mutation into the mouse genome. We show here that mutations of Asp580 in the mFSHR significantly increase the basal receptor activity. D580H and D580Y mutations of mFSHR bind FSH, but the activity of the former is neither ligand-dependent nor promiscuous towards LH/human choriogonadotropin stimulation. Transgenic expression of mFshr(D580H) in granulosa cells leads to abnormal ovarian structure and function in the form of hemorrhagic cysts, accelerated loss of small follicles, augmented granulosa cell proliferation, increased estradiol biosynthesis, and occasional luteinized unruptured follicles or teratomas. The most affected mFshr(D580H) females are infertile with disturbed estrous cycle and decreased gonadotropin and increased prolactin levels. Increased estradiol and prolactin apparently underlie the enhanced development of the mammary glands, adenomatous pituitary growth, and lipofuscin accumulation in the adrenal gland. The influence of the mFSHR(D580Y) mutation is milder, mainly causing hemorrhagic cysts in transgenic mFSHR(D580Y) and mFSHR(D580Y) -knock-in mice. The results demonstrate that gain-of-function mutations of the FSHR in mice bring about distinct and clear changes in ovarian function, informative in the search of similar mutations in humans.

Recombinant FSH in the treatment of oligozoospermia

BACKGROUND

FSH plays a crucial role in human reproduction. Treatment with gonadotrophins has been shown to be effective in males affected by hypogonadotrophic hypogonadism. The success of this treatment has brought about the utilization of the same therapy in infertile oligozoospermic subjects, aimed at obtaining increased sperm count. This physiological role in spermatogenesis has induced various attempts to treat idiopathic oligozoospermic men with FSH, often inducing the restoration of normal spermatogenesis and spontaneous pregnancy.

OBJECTIVE

To evaluate clinical efficacy of recombinant FSH in male infertility.

METHODS

Evaluation of pharmacokinetic, pharmacodynamic properties, efficacy and safety of this hormone preparation, on the basis of the data published in literature.

CONCLUSIONS

Recombinant FSH is effective, safe and well tolerated. Treatment with this hormone may represent a valid tool for infertile men. However it should be performed on selected patients utilizing some predictive parameters able to identify a priori responder subjects with high probability.

Mechanisms of protein kinase C signaling in the modulation of 3',5'-cyclic adenosine monophosphate-mediated steroidogenesis in mouse gonadal cells

The protein kinase C (PKC) signaling pathway plays integral roles in the expression of the steroidogenic acute regulatory (StAR) protein that regulates steroid biosynthesis in steroidogenic cells. PKC can modulate the activity of cAMP/protein kinase A signaling involved in steroidogenesis; however, its mechanism remains obscure. In the present study, we demonstrate that activation of the PKC pathway, by phorbol 12-myristate 13-acetate (PMA), was capable of potentiating dibutyryl cAMP [(Bu)(2)cAMP]-stimulated StAR expression, StAR phosphorylation, and progesterone synthesis in both mouse Leydig (MA-10) and granulosa (KK-1) tumor cells. The steroidogenic potential of PMA and (Bu)(2)cAMP was linked with phosphorylation of ERK 1/2; however, inhibition of the latter demonstrated varying effects on steroidogenesis. Transcriptional activation of the StAR gene by PMA and (Bu)(2)cAMP was influenced by several factors, its up-regulation being dependent on phosphorylation of the cAMP response element binding protein (CREB). An oligonucleotide probe containing a CREB/activating transcription factor binding region in the StAR promoter was found to bind nuclear proteins in PMA and (Bu)(2)cAMP-treated MA-10 and KK-1 cells. Chromatin immunoprecipitation studies revealed that the induction of phosphorylated CREB was tightly correlated with in vivo protein-DNA interactions and recruitment of CREB binding protein to the StAR promoter. Ectopic expression of CREB binding protein enhanced CREB-mediated transcription of the StAR gene, an event that was markedly repressed by the adenovirus E1A oncoprotein. Further studies demonstrated that the activation of StAR expression and steroid synthesis by PMA and (Bu)(2)cAMP was associated with expression of the nuclear receptor Nur77, indicating its essential role in hormone-regulated steroidogenesis. Collectively, these findings provide insight into the mechanisms by which PKC modulates cAMP/protein kinase A responsiveness involved in regulating the steroidogenic response in mouse gonadal cells.

Mechanisms of relaxin receptor (LGR7/RXFP1) expression and function

The LGR7/RXFP1 and LGR8/RXFP2 receptors are unique receptors among the G-protein-coupled receptors (GPCRs) in having a low-density lipoprotein class A (LDL-A) module. Their complex gene organization, among the intron-richest of the GPCRs, suggests that alternative splicing is a common occurrence. We have therefore investigated the role of the LDL-A module and shown the identity, expression, and functions of three LGR7 splice variants in the human decidua. Point mutations of conserved residues or complete deletion of the LDL-A module resulted in loss of the cAMP response to relaxin. Its glycosylation also impacted LGR7 cell surface delivery and therefore receptor activation. The wild-type (WT) LGR7 was expressed as both precursor and mature forms, but deletion of the LDL-A module resulted in expression of only the mature form. Three new alternatively spliced variants of LGR7 were identified, all containing a truncated extracellular region. Their functional characterization showed them exerting dominant negative effects on the WT LGR7 by preventing its homodimerization, maturation, and subsequent trafficking to the cell surface, resulting in loss of function. In summary, different mechanisms have been identified for controlling the cell surface expression and function of the LGR7 protein which are likely to be significant for the role of relaxin in human parturition.

Follicle-stimulating hormone treatment in oligozoospermic patients

Follicle-stimulating hormone (FSH) plays a crucial role in human reproduction. Already, in the fetal and neonatal developmental stages, FSH activates the proliferation of the Sertoli cells and successively, in the pubertal phase, induces the mitotic activity of the spermatogonia and supports cellular differentiation to the round spermatid stage. This physiological role in spermatogenesis has induced various attempts to treat idiopathic oligozoospermic men with FSH. It is well known that treatment with gonadotrophins is very effective in subjects affected by hypogonadotropic hypogonadism, often leading to the restoration of normal spermatogenesis. The success of this treatment in these men has brought the utilization of the therapy with FSH in infertile oligozoospermic subjects, aimed at obtaining a quantitative increase in sperm count. However, the results obtained so far are still controversial. In this article, the literature is reviewed and the authors' experience on using FSH treatment in oligozoospermic subjects is discussed.

Molecular characterization of follicle stimulating hormone receptor (FSHR) gene in the Indian river buffalo (Bubalus bubalis)

Follicle stimulating hormone (FSH) plays a central role in regulation of ovarian function in mammals. The actions of follicle stimulating hormone are mediated through receptors present on the granulosa cells of the ovary. In the present study we have cloned and characterized the FSHR gene of buffalo. Sequence analysis indicated that the buffalo FSHR cDNA sequence comprised of an open reading frame of 2085bp encoding a 695 amino acid protein. Its nucleotide sequence showed more than 80% similarity to the homologous genes of mammalian species. At amino acid level buffalo FSHR exhibited a high percentage (84-96.7%) of identity with the corresponding mammalian homologs. This is the first isolation and characterization of FSHR cDNA from buffalo ovary.

Gonadotropin hormone and receptor sequences from model teleost species

Fish offer some advantages for the study of vertebrate reproductive physiology. Only a few of the genes encoding the components of the hypothalamic-pituitary-gonadal axis have been identified from model teleosts. This study describes a combination of database searching and molecular approaches to identify the FSH and LH gonadotropin beta-subunits (fshb and lhb, respectively), and the LH receptor (lhr) from two model teleost species: zebrafish (Danio rerio) and Fugu (Takifugu rubripes). Sequence and phylogenetic analyses were used to examine the relationships that exist between gonadotropins and their receptors from species representing several piscine orders. The gonadotropin alpha-subunit (Cga) is highly conserved among teleosts and tetrapods. The presence of a genomic pseudogene (cgap) was also noted in zebrafish. Generally, teleostean FSHbeta protein sequences share less identity with each other than do LHbeta protein sequences, supporting the hypothesis that FSHbeta diverged more rapidly during teleost evolution. Interestingly, and uniquely, zebrafish Fshb lacked two highly conserved cysteine residues in the "determinant loop" which is thought to contribute towards receptor binding and specificity. Teleost gonadotropin receptor sequences clearly diverged into two distinct groups, FSHR and LHR. As has been seen with mammalian gonadotropin receptor transcripts, splice variants of zebrafish lhr were also observed.

Cloning, expression, and functional characterization of relaxin receptor (leucine-rich repeat-containing g protein-coupled receptor 7) splice variants from human fetal membranes

The relaxin receptor [leucine-rich repeat-containing G protein-coupled receptor 7 (LGR7)] belongs to the leucine-rich repeat containing G protein-coupled receptors subgroup C. Three new LGR7 splice variants have been cloned from the human fetal membranes and shown to be truncated versions of the full-length receptor, encoded by different lengths of the extracellular domain. The expression of their mRNAs has been confirmed by both qualitative and quantitative PCR and shown to be higher in the chorion and decidua before, compared with after, spontaneous labor. When HEK293 cells were transfected with each LGR7 splice variant, their proteins were retained within the endoplasmic reticulum. However, the protein for the shortest variant was also secreted into the medium. We have characterized the intracellular functions and effects of these LGR7 variants on the function of the wild-type (WT)-LGR7. In coexpression studies, each splice variant interacted directly with the WT-LGR7 and exerted a dominant-negative effect on cAMP accumulation by the WT-LGR7 after relaxin treatment. This interaction resulted in the sequestration of the WT-LGR7 inside the cells by down-regulation of its maturation and cell surface delivery. The constitutive homodimerization of WT-LGR7 has been shown here to take place in the endoplasmic reticulum, and the presence of any one of the splice variants decreased this by the formation of heterodimers with the WT-LGR7, supporting the view that homodimerization is a prerequisite for receptor trafficking to the cell surface. These data suggest that the dominant-negative effects of the LGR7 splice variants expressed in the chorion and decidua could be functionally significant in the peripartal period by inhibiting the function of WT-LGR7 and dampening the responsiveness of these tissues to endogenous relaxin.

FSH stimulates ovarian cancer cell growth by action on growth factor variant receptor

A number of FSH receptor (FSH-R) isoforms with distinct structural motifs and signaling paradigms have been described, including a single transmembrane domain variant that functions as a growth factor type receptor (FSH-R3). This study tested the hypothesis that FSH can stimulate ovarian cancer cell proliferation by acting on FSH-R3, using the tumorigenic mouse ovarian surface epithelial cell (MOSEC) line ID8. FSH enhanced ID8 proliferation in a concentration-dependent fashion. Moreover, FSH-treatment of ID8 elicited intracellular events consistent with activation of FSH-R3 and distinct from those associated with activation of the canonical G-protein coupled FSH-R isoform (FSH-R1). Specifically, the FSH-R3 signaling pathway included cAMP-independent activation of ERK downstream of an SNX-482 sensitive component likely to be the Cav2.3 calcium channel. Northern analysis using probes specific for exons 7 and 11 of FSH-R identified consistently only one 1.9kb transcript. Immunoblot analysis confirmed expression of FSH-R3 but not FSHR-1 in ID8. Together, these data suggest that FSH-R3 signaling promotes proliferation of ovarian cancer cells.

Relaxin family peptide receptors--former orphans reunite with their parent ligands to activate multiple signalling pathways

The relaxin family peptides, although structurally closely related to insulin, act on a group of four G protein-coupled receptors now known as Relaxin Family Peptide (RXFP) Receptors. The leucine-rich repeat containing RXFP1 and RXFP2 and the small peptide-like RXFP3 and RXFP4 are the physiological targets for relaxin, insulin-like (INSL) peptide 3, relaxin-3 and INSL5, respectively. RXFP1 and RXFP2 have at least two binding sites--a high-affinity site in the leucine-rich repeat region of the ectodomain and a lower-affinity site in an exoloop of the transmembrane region. Although they respond to peptides that are structurally similar, RXFP3 and RXFP4 demonstrate distinct binding properties with relaxin-3 being the only peptide that can recognize these receptors in addition to RXFP1. Activation of RXFP1 or RXFP2 causes increased cAMP and the initial response for both receptors is the resultant of Gs-mediated activation and G(oB)-mediated inhibition of adenylate cyclase. With RXFP1, an additional delayed increase in cAMP involves betagamma subunits released from G(i3). In contrast, RXFP3 and RXFP4 inhibit adenylate cyclase and RXFP3 causes ERK1/2 phosphorylation. Drugs acting at RXFP1 have potential for the treatment of diseases involving tissue fibrosis such as cardiac and renal failure, asthma and scleroderma and may also be useful to facilitate embryo implantation. Activators of RXFP2 may be useful to treat cryptorchidism and infertility and inhibitors have potential as contraceptives. Studies of the distribution and function of RXFP3 suggest that it is a potential target for anti-anxiety and anti-obesity drugs.

The tale of follitropin receptor diversity: a recipe for fine tuning gonadal responses?

The original concept (dogma) of a single FSH receptor entity coupling to G(s) protein to activate adenylate cyclase and producing cAMP as second messenger appears inadequate to explain pleiotropic actions of the hormone. The identification and expression of alternatively spliced gonadotropin receptors, suggest that alternative splicing could serve as a mechanism for creating receptor diversity. Studies focused on sheep and mouse gonadal tissues show that the single large gene of approximately 250kb is a modular structure whose pre-mRNA undergoes alternative splicing creating several subtypes (at least four FSH-R1 to R4 identified to date). With segments of the N-terminus that are identical different topographies are generated by differing carboxyl termini. The same gene thus produces receptor types with different motifs that can display dominant positive, dominant negative, growth factor/cytokine type and potentially soluble binding protein features. Functional relevance is shown by modulation of receptor variants during hormonal stimulation. Presence of equivalent segments of the gene in the human and bovine suggests conservation and predicts similarity in structures and function. Thus, the complex cellular biology of follitropin receptors that may interact differently with polymorphic forms (glycosylation variants) of FSH represents an intricate scheme to regulate hormone signaling.

Transcriptional regulation of the FSH receptor: new perspectives

The cell-surface receptor for the gonadotropin follicle-stimulating hormone (FSH) is expressed exclusively on Sertoli cells of the testis and granulosa cells of the ovary. FSH signal transduction through its receptor (Fshr) is critical for the timing and maintenance of normal gametogenesis in the mammalian gonad. In the 13 years since the gene encoding Fshr was first cloned, the mechanisms controlling its transcription have been extensively examined, but a clear understanding of what drives its unique cell-specificity remains elusive. Current knowledge of basal Fshr transcription highlights the role of an E-box in the proximal promoter which is bound by the basic helix-loop-helix transcription factors upstream stimulatory factor 1 (Usf1) and Usf2. Recent studies utilizing knockout mice and chromatin immunoprecipitation validated the importance of Usf to Fshr transcription and demonstrated a sexually dimorphic requirement for the Usf proteins to maintain normal Fshr expression. Studies have also shown that the promoter region itself is insufficient for appropriate Fshr expression in transgenic mice, indicating Fshr transcription depends on regulatory elements that lie outside of the promoter. Identification of such elements has been propelled by recent availability of genome sequence data, which facilitated studies using comparative genomics, DNase I hypersensitivity mapping, and transgenic analysis with large fragments of DNA. This review will focus on the current understanding of transcriptional regulatory processes that control expression of rat Fshr, including recent advances from our laboratory.

Characterization of Novel Splice Variants of LGR7 and LGR8 Reveals That Receptor Signaling Is Mediated by Their Unique Low Density Lipoprotein Class A Modules

The relaxin and insulin-like peptide 3 receptors, LGR7 and LGR8, respectively, are unique members of the leucine-rich repeat-containing G-protein-coupled receptor (LGR) family, because they possess an N-terminal motif with homology to the low density lipoprotein class A (LDLa) modules. By characterizing several LGR7 and LGR8 splice variants, we have revealed that the LDLa module directs ligand-activated cAMP signaling. The LGR8-short variant encodes an LGR8 receptor lacking the LDLa module, whereas LGR7-truncate, LGR7-truncate-2, and LGR7-truncate-3 all encode truncated secreted proteins retaining the LGR7 LDLa module. LGR8-short and an engineered LGR7 variant missing its LDLa module, LGR7-short, bound to their respective ligands with high affinity but lost their ability to signal via stimulation of intracellular cAMP accumulation. Conversely, secreted LGR7-truncate protein with the LDLa module was able to block relaxin-induced LGR7 cAMP signaling and did so without compromising the ability of LGR7 to bind to relaxin or be expressed on the cell membrane. Although the LDLa module of LGR7 was N-glycosylated at position Asn-14, an LGR7 N14Q mutant retained relaxin binding affinity and cAMP signaling, implying that glycosylation is not essential for optimal LDLa function. Using real-time PCR, the expression of mouse LGR7-truncate was detected to be high in, and specific to, the uterus of pregnant mice. The differential expression and evolutionary conservation of LGR7-truncate further suggests that it may also play an important role in vivo. This study highlights the essential role of the LDLa module in LGR7 and LGR8 function and introduces a novel model of GPCR regulation.

Splice variants of the relaxin and INSL3 receptors reveal unanticipated molecular complexity

LGR7 and LGR8 are G protein-coupled receptors that belong to the leucine-rich repeat-containing G-protein coupled receptor (LGR) family, including the thyroid-stimulating hormone (TSH), LH and FSH receptors. LGR7 and LGR8 stimulate cAMP production upon binding of the cognate ligands, relaxin and insulin-like peptide 3 (INSL3), respectively. We cloned several novel splice variants of both LGR7 and LGR8 and analysed the function of four variants. LGR7.1 is a truncated receptor, including only the N-terminal region of the receptor and two leucine rich repeats. In contrast, LGR7.2, LGR7.10 and LGR 8.1 all contain an intact seven transmembrane domain and most of the extracellular region, lacking only one or two exons in the ectodomain. Our analysis demonstrates that although LGR7.10 and LGR8.1 are expressed at the cell surface, LGR7.2 is predominantly retained within cells and LGR7.1 is partially secreted. mRNA expression analysis revealed that several variants are co-expressed in various tissues. None of these variants were able to stimulate cAMP production following relaxin or INSL3 treatment. Unexpectedly, we did not detect any direct specific relaxin or INSL3 binding on any of the splice variants. The large number of receptor splice variants identified suggests an unforeseen complexity in the physiology of this novel hormone-receptor system.

Silencing of Fshr occurs through a conserved, hypersensitive site in the first intron

Expression of the FSH receptor (Fshr) is restricted to testicular Sertoli cells and ovarian granulosa cells, thereby limiting the direct targets of FSH action to these somatic cells of the gonads. Earlier studies indicate that transcription of Fshr in the gonads requires elements outside the gene's immediate 5' flanking sequence. To help uncover candidate regulatory sequences, comparative genomics and deoxyribonuclease I hypersensitivity mapping were employed. A total of 156 evolutionarily conserved sequences were found, and partial deoxyribonuclease I hypersensitivity mapping across 45 kb of 5' flanking sequence and the first intron identified four hypersensitive sites, DHS1-4. Notably, DHS1 and DHS2 localized to conserved sites in the promoter region and exon 1 and correlated with the active state of the gene. DHS3 also corresponded to a conserved site (site 7) but was more pronounced in nonexpressing myoid cells, suggesting a role in gene silencing. Transient transfection analysis of DHS3 confirmed its role in gene silencing, a function that was promoter, cell type, and position dependent. Protein-DNA binding studies on DHS3 revealed that octamer transcription factor 1 (OCT-1) and GATA-4 bound site 7, in vitro, and transient transfection analysis showed that their binding sites were required for silencing activity. Furthermore, chromatin immunoprecipitation revealed that OCT-1 bound to site 7 in the endogenous gene, but only in myoid cells. In contrast, GATA-1 bound site 7 predominantly in Sertoli cells, suggesting that it attenuates silencer activity. The findings reveal that OCT-1 binds within DHS3 to silence Fshr transcription and implicate members of the GATA family in the modulation of this activity.

Downregulation of Follicle-Stimulating Hormone (FSH)-Receptor Messenger RNA Levels in the Hamster Ovary: Effect of the Endogenous and Exogenous FSH1

Although gonadotropins have been reported to downregulate FSH-receptor (FSHR) mRNA levels in the ovaries of female rats, the effect of the gonadotropin surge, particularly FSH, on hamster follicular FSHR mRNA levels warrants further examination. The objectives of the present study were to clone and determine the complete FSHR cDNA sequence of the hamster and to delineate the effects of endogenous and exogenous FSH on the steady-state levels of ovarian FSHR mRNA. Complete FSHR cDNA was derived from hamster ovarian total RNA by the strategy of 3'- and 5'-rapid amplification of cDNA ends. Ovaries were obtained before and after the endogenous gonadotropin surge or exogenous FSH administration, and the steady-state levels of FSHR mRNA were assessed by Northern blot hybridization. Cloned FSHR cDNA consists of a reading frame corresponding to exons 1-10 of the human FSHR gene and the 5'- and 3'-untranslated regions. The nucleic acid and amino acid sequences of the reading frame were at least 87% and 92% identical, respectively, to that of human, rat, and mouse FSHR. Furthermore, the amino acid sequence contained seven transmembrane domains characteristic of the FSHR. The steady-state levels of FSHR mRNA increased from estrus (Day 1) to reach a peak on proestrus (Day 4) noon; however, significant attenuation was noted following the gonadotropin surge, which was blocked by phenobarbital. Exogenous FSH also downregulated, both dose- and time-dependently, ovarian FSHR mRNA levels. These data indicate that the nucleic acid sequence of hamster FSHR has been identified and that FSH modulates FSHR mRNA levels in the hamster ovary.

Responsiveness of bovine cumulus-oocyte-complexes (COC) to porcine and recombinant human FSH, and the effect of COC quality on gonadotropin receptor and Cx43 marker gene mRNAs during maturation in vitro

Substantially less development to the blastocyst stage occurs in vitro than in vivo and this may be due to deficiencies in oocyte competence. Although a large proportion of bovine oocytes undergo spontaneous nuclear maturation, less is known about requirements for proper cytoplasmic maturation. Commonly, supraphysiological concentrations of FSH and LH are added to maturation media to improve cumulus expansion, fertilization and embryonic development. Therefore, various concentrations of porcine FSH (pFSH) and recombinant human FSH (rhFSH) were investigated for their effect on bovine cumulus expansion in vitro. Expression of FSHr, LHr and Cx43 mRNAs was determined in cumulus-oocyte complexes to determine whether they would be useful markers of oocyte competence. In serum-free media, only 1000 ng/ml pFSH induced marked cumulus expansion, but the effect of 100 ng/ml pFSH was amplified in the presence of 10% serum. In contrast, cumulus expansion occurred with 1 ng/ml rhFSH in the absence of serum. FSHr mRNA was highest at 0-6 h of maturation, then abundance decreased. Similarly, Cx43 mRNA expression was highest from 0-6 h but decreased by 24 h of maturation. However, the relative abundance of LHr mRNA did not change from 6-24 h of maturation. Decreased levels of FSHr, LHr and Cx43 mRNAs were detected in COCs of poorer quality. In conclusion, expansion of bovine cumulus occurred at low doses of rhFSH in serum-free media. In summary, FSHr, LHr and Cx43 mRNA abundance reflects COC quality and FSHr and Cx43 mRNA expression changes during in vitro maturation; these genes may be useful markers of oocyte developmental competence.

Failure of normal Leydig cell development in follicle-stimulating hormone (FSH) receptor-deficient mice, but not FSHbeta-deficient mice: role for constitutive FSH receptor activity

Previous studies have suggested that FSH may be involved in regulation of Leydig cell function. We have examined this directly using two mouse models with null mutations in either the FSH beta-subunit (FSHbetaKO mice) or the FSH receptor (FSHRKO mice). Circulating LH levels were normal in adult FSHbetaKO mice, but were significantly increased in FSHRKO mice. Intratesticular testosterone levels increased normally in FSHbetaKO mice from birth to adulthood, whereas testosterone levels in FSHRKO mice failed to increase normally after puberty and were significantly reduced in adult animals. This was associated with reduced levels of mRNA encoding cytochrome P450 side-chain cleavage, 3beta-hydroxysteroid dehydrogenase type VI, and steroidogenic acute regulatory protein in FSHRKO mice. Leydig cell number was normal in FSHbetaKO mice during development, but in FSHRKO mice Leydig cell number increased slowly after puberty and was significantly reduced in the adult animal. Transfection studies showed that the FSHR exhibits constitutive activity in the absence of agonist stimulation. The results indicate, therefore, that Sertoli cells regulate the development of Leydig cell number and that constitutive activity within the FSHR is sufficient to stimulate this process. The presence of the hormone itself is not required when circulating LH levels are adequate.

Structure and expression of the follicle-stimulating hormone receptor gene in a marsupial, Macropus eugenii

Follicle stimulating hormone (FSH) is essential for folliculogenesis. The function of FSH is mediated through its receptor (FSHr) and modulation of the receptor is thought to be the mechanism by which the responsiveness of follicles to gonadotrophins is regulated. FSHr is alternatively spliced to produce several transcripts in all eutherian species studied. However, controversy exists over the significance of alternatively spliced transcripts. In this study, we cloned and characterised the tammar wallaby (Macropus eugenii) FSHr gene and examined its expression. Comparison of gene structure and function between marsupials and eutherians enables identification of conserved features that are likely to be of functional significance. Tammar FSHr shares 94% amino acid similarity with human FSHr and is expressed in both the adult testis and ovary suggesting a similar function for this gene in both marsupials and eutherians. Tammar FSHr undergoes alternate splicing to produce four transcripts consistent with the splice variants seen in eutherians. These results strongly suggest that alternate splicing is of functional significance in the ovary since it has remained a highly conserved character of this gene for over 100 million years of divergent evolution.

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.

Nerve growth factor induces the expression of functional FSH receptors in newly formed follicles of the rat ovary

The neurotrophin nerve growth factor (NGF) and its two membrane-anchored receptors are expressed in the developing ovary before the organization of the first primordial follicles. In the absence of NGF, the growth of primordial follicles is retarded, indicating that NGF contributes to facilitating early follicular development. The present experiments were undertaken to determine whether NGF can also be involved in the differentiation process by which ovarian follicles become responsive to gonadotropins. Treatment of 2-d-old rat ovaries in organ culture with NGF increased FSH receptor (FSHR) mRNA within 8 h of exposure. This effect was cAMP-independent but additive to the cAMP-mediated increase in FSHR gene expression induced by either forskolin or vasoactive intestinal peptide, a neurotransmitter previously shown to induce FSHR formation in neonatal rat ovaries. After NGF treatment, the ovary acquired the capacity of responding to FSH with cAMP formation and preantral follicular growth, indicating that exposure to the neurotrophin resulted in the formation of biologically active FSHRs. Quantitative measurement of FSHR mRNA demonstrated that the content of FSHR mRNA is reduced in the ovaries of mice carrying a null mutation of the NGF gene. These results indicate that one of the functions of NGF in the developing ovary is to facilitate the differentiation process by which early growing follicles become gonadotropin-dependent during postnatal life, and that it does so by increasing the synthesis of FSHRs.

Alternatively spliced variants of the follicle-stimulating hormone receptor gene in the testis of infertile men

OBJECTIVE

To investigate whether or not alternatively spliced variants of the FSH receptor gene occur in human testis and whether the presence of the splicing variants is associated with spermatogenic defects and serum FSH concentration in infertile men.

DESIGN

A prospective case control study.

SETTING

An IVF clinic and infertility laboratory at a university hospital.

PATIENT(S)

Forty-three infertile patients undergoing testicular biopsy.

INTERVENTION(S)

Total RNA was extracted from the testicular tissues and used for reverse transcriptase-polymerase chain reaction (RT-PCR).

MAIN OUTCOME MEASURE(S)

Expression pattern was analyzed by nested RT-PCR using primers designed to amplify a fragment of FSH receptor gene. PCR products of splicing variants were cloned and sequenced.

RESULT(S)

The PCR products showed three kinds of additional bands corresponding to alternatively spliced isoforms of the FSH receptor gene. Exon 9 deleted variant was detected in all patients and inclusion variant of small extra exon was detected in 64% (9/14) of the patients with normal spermatogenesis and 34% (10/29) of the patients with spermatogenic defects. The presence of inclusion variant was not significantly associated with spermatogenic defects but was associated with a low level of serum FSH. On the other hand, exon 6 deleted variant was detected in only one patient having a high level of FSH concentration (30 IU/L) and Sertoli cell only syndrome.

CONCLUSION(S)

We identified three different types of alternatively spliced variants of the human FSH receptor. However, it is not clear whether or not there is an association between three variants and spermatogenic defects.

Zebrafish as a model for vertebrate reproduction: characterization of the first functional zebrafish (Danio rerio) gonadotropin receptor

Vertebrate reproduction is tightly regulated by conserved glycoprotein hormones produced by the pituitary gland. Follicle-stimulating hormone (FSH) in tetrapods and gonadotropic hormone I (GTH-I) in fishes are orthologous glycoprotein hormones that control the timing of egg production and the number of eggs produced. Zebrafish, a well-established genetic model for developmental biology, also offers potential advantages for studies of reproductive toxicology, especially for modeling the impact of pollutants on fish reproductive processes. To facilitate these studies we have identified, expressed, and characterized the zebrafish GTH-I receptor. This receptor (zfGTHR-I)exhibits strong sequence similarity to the tetrapod FSH receptors and to GTHR-I from salmon and catfish. Human 293 cells transfected with zfGTHR-I exhibit increased cAMP levels after treatment with carp pituitary extracts or human FSH, but not when treated with a ligand to a related receptor (human chorionic gonadotropin). Northern blotting and RT-PCR analyses indicate that zfGTHR is expressed in ovaries from sexually mature fish, but not in immature fish. Several alternative splice variants of the receptor affecting putative exons 2-4 that encode dramatically shortened receptor fragments lacking the transmembrane domain as well as regions previously implicated in ligand binding were identified by RT-PCR. The zfGTHR-I sequence opens the way to study effects of genetic mutations or chemicals on ovarian zfGTHR-I expression and function in zebrafish.

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.

Alternative ribonucleic acid processing in endocrine systems

Alternative RNA processing is a mechanism for creation of protein diversity through selective inclusion or exclusion of RNA sequence during posttranscriptional processing. More than one-third of human pre-mRNAs undergo alternative RNA processing modification, making this a ubiquitous biological process. The protein isoforms produced have distinct and sometimes opposite functions, underscoring the importance of this process. This review focuses on important endocrine genes regulated by alternative RNA processing. We discuss how diverse events such as spermatogenesis or GH action are regulated by this process. We focus on several endocrine (calcitonin/calcitonin gene-related peptide) and nonendocrine (Drosophila doublesex and P-element and mouse c-src) examples to highlight recent progress in the elucidation of molecular mechanisms regulating this process. Finally, we outline methods (model systems and techniques) used by investigators in this field to study processing of individual pre-mRNAS:

The promoter of murine follicle-stimulating hormone receptor: functional characterization and regulation by transcription factor steroidogenic factor 1

The promoter of the FSH receptor (R) gene has been cloned from several species. Although some of its regulatory elements have been identified, its function still remains poorly characterized. Using transient transfections of luciferase reporter constructs, driven by various fragments of the murine (m) FSHR promoter, we identified a cell-specific promoter region. This domain is located in the distal part of the mFSHR promoter, -1,110 to -1,548 bp upstream of the translation initiation site, and it contains two steroidogenic factor 1 (SF-1) like binding sites (SLBS). The cellular levels of SF-1 mRNA and protein closely correlated in various steroidogenic cell lines with activity of the transfected mFSHR promoter/luciferase reporter construct carrying the distal activator domain. A dose-dependent increase in FSHR promoter activity was shown in nonsteroidogenic HEK 293 cells transiently transfected with SF-1 cDNA. SF-1 was found to bind to a nonconsensus 5'-CAAGGACT-3' SLBS-3 motif in the distal part of the promoter; formation of the SF-1/SLBS-3 complex could be reversed by addition of SF-1 antibody. Mutation in the SLBS-3 domain abolished the SF-1/SLBS-3 complex in gel-shift assays and led to a significant loss of SF-1-mediated mFSHR promoter activity. The second SLBS appeared to have minor role in SF-1-regulated mFSHR expression. In conclusion, we have identified a regulatory domain in the mFSHR promoter participating in the cell-specific regulation of FSHR expression. We demonstrated for the first time that the mFSHR promoter possesses functional SF-1 binding sites and thus belongs to the group of SF-1-regulated genes. These findings provide further evidence for the key role of SF-1 in the regulation of genes involved in gonadal differentiation and endocrine functions.

Human follicle stimulating hormone receptor variants lacking transmembrane domains display altered post-translational conformations

Variant splicing of gonadotropin receptor mRNA commonly occurs, however expression of receptor protein variants and their trafficking has yet to be studied in detail. To determine receptor variant trafficking and intracellular processing in mammalian cells, the intracellular fate of intentionally truncated variants of human follicle stimulating hormone receptor (hFSH-R) expressed in CHO cells was examined. Monoclonal antibodies (mAbs) were made against the hFSH-R's extracellular domain (ECD) expressed in insect cells. Four mAbs 106.156, 106.290, 106.318, and 106.263 were chosen as probes. Epitope mapping using synthetic peptides, and truncated hFSH-R variants revealed that mAb 106.156 bound to ECD residues 183-220, while mAbs 106.318, 106.290, 106.263 bound ECD residues 300-331. Immunofluorescence microscopy showed that mAbs 106.318 and 106.156 stained the surface of fixed, intact CHO cells expressing wild type hFSH-R. However, following cell permeabilization all four antibodies stained hFSH-R in Golgi and endoplasmic reticulum. Permeabilized cells expressing truncated variants ECD213 and ECD254 showed staining accumulated in the endoplasmic reticulum/nuclear envelope continuum. ECD335/His was found to accumulate in extended endoplasmic reticulum (ER). The ER location of ECD335/His was confirmed by double labeling experiments with concanavalin A and ECD mAb. Glycosidase digestion followed by Western blot analysis show ECD213 and ECD335/His to be glycosylated, but not ECD254. Both glycosylated truncated hFSH-R variants were sensitive to peptide-N-glycanase F and endoglycosidase H but insensitive to neuraminidase indicating that these variants possess high mannose type oligosaccharides. Thus truncated hFSH-R variants do not reach the medial or trans Golgi where high mannose oligosaccharides are trimmed and sialic acid is added. These data suggest that the conformation the ECD of the wild type receptor is different from the ECD alone expressed in the endoplasmic reticulum. This information suggests that the ECD serves two distinct roles; the first is to bind FSH and the other is likely to contact the endodomain of the receptor, which presumably leads to activation of the endodomain for signal transduction.

Follicle-stimulating hormone ligand and receptor mutations, and gonadal dysfunction

In contrast to the general contention, infertility can be an inherited condition. Some of the genetic causes of male and female infertility have turned out to be due to inactivating mutations in the gonadotropin and gonadotropin receptor genes. The topic of the present text is to review current knowledge on mutations affecting the function of follicle-stimulating hormone (FSH). This gonadotropin, by binding to its specific G protein-coupled cell membrane receptor (FSHR), is important for normal gonadal function. Mutations affecting gonadotropin genes are extremely rare, but recent genetic studies have revealed that the pathogenesis of subfertility or infertility can be due to mutations in the FSH receptor (FSHR) gene. While mutations affecting FSHR are sporadic, polymorphism of the FSHR gene seems to be a common phenomenon. To date, six inactivating and only one activating mutation have been detected in the FSHR gene. In contrast to LHR gene, the majority of these mutations affect the extracellular domain of the receptor. Together with animal models using the transgenic and knock-out approaches, systematic analysis of alterations in the FSHR gene increases our knowledge on the structure and function of the FSHR and demonstrates that the integrity of each FSHR segment is required for proper expression of the fully active protein and for normal gonadal function. Mutations in the FSHR gene have different consequences in the reproductive function depending on the sex of the patient: while normal ovarian function is critically dependent on FSH, male fertility is possible with minimal or absent FSH action.