Steroidogenic factor 1 (SF-1) is essential for ovarian development and function

Role of NR5A1 Gene Mutations in Disorders of Sex Development: Molecular and Clinical Features

Disorders/differences of sex development (DSDs) are defined as broad, heterogenous groups of congenital conditions characterized by atypical development of genetic, gonadal, or phenotypic sex accompanied by abnormal development of internal and/or external genitalia. NR5A1 gene mutation is one of the principal genetic alterations implicated in causing DSD. This review outlines the role of NR5A1 gene during the process of gonadal development in humans, provides an overview of the molecular and functional characteristics of NR5A1 gene, and discusses potential clinical phenotypes and additional organ diseases due to NR5A1 mutations. NR5A1 mutations were analyzed in patients with 46,XY DSD and 46,XX DSD both during the neonatal and pubertal periods. Loss of function of the NR5A1 gene causes several different phenotypes, including some associated with disease in additional organs. Clinical phenotypes may vary, even among patients carrying the same NR5A1 variant, indicating that there is no specific genotype-phenotype correlation. Genetic tests are crucial diagnostic tools that should be used early in the diagnostic pathway, as early as the neonatal period, when gonadal dysgenesis is the main manifestation of NR5A1 mutation. NR5A1 gene mutations could be mainly associated with amenorrhea, ovarian failure, hypogonadism, and infertility during puberty. Fertility preservation techniques should be considered as early as possible.

SF-1 Induces Nuclear PIP2

Metazoan cell nuclei contain non-membrane pools of the phosphoinositide lipid PI(4,5)P2 (PIP2), but how this hydrophobic lipid exists within the aqueous nucleoplasm remains unclear. Steroidogenic Factor-1 (NR5A1, SF-1) is a nuclear receptor that binds PIP2 in vitro, and a co-crystal structure of the complex suggests the acyl chains of PIP2 are hidden in the hydrophobic core of the SF-1 protein while the PIP2 headgroup is solvent-exposed. This binding mode explains how SF-1 can solubilize nuclear PIP2; however, cellular evidence that SF-1 expression associates with nuclear PIP2 has been lacking. Here, we examined if tetracycline induction of SF-1 expression would associate with nuclear accumulation of PIP2, using antibodies directed against the PIP2 headgroup. Indeed, tetracycline induction of wild-type SF-1 induced a signal in the nucleus of HEK cells that cross-reacts with PIP2 antibodies, but did not cross-react with antibodies against the lower abundance phosphoinositide PI(3,4,5)P3 (PIP3). The nuclear PIP2 signal co-localized with FLAG-tagged SF-1 in the nuclear compartment. To determine if the nuclear PIP2 signal was dependent on the ability of SF-1 to bind PIP2, we examined a "pocket mutant" of SF-1 (A270W, L345F) shown to be deficient in phospholipid binding by mass spectrometry. Tetracycline induction of this pocket mutant SF-1 in HEK cells failed to induce a detectable PIP2 antibody cross-reactive signal, despite similar Tet-induced expression levels of the wild-type and pocket mutant SF-1 proteins in these cells. Together, these data are the first to suggest that expression of SF-1 induces a PIP2 antibody cross-reactive signal in the nucleus, consistent with X-ray crystallographic and biochemical evidence suggesting SF-1 binds PIP2 in human cells.

Development of the human ovary: Fetal through pubertal ovarian morphology, folliculogenesis and expression of cellular differentiation markers

A definition of normal human fetal and early postnatal ovarian development is critical to the ability to accurately diagnose the presence or absence of functional ovarian tissue in clinical specimens. Through assembling an extensive histologic and immunohistochemical developmental ontogeny of human ovarian specimens from 8 weeks of gestation through 16 years of postnatal, we present a comprehensive immunohistochemical mapping of normal protein expression patterns in the early fetal through post-pubertal human ovary and detail a specific expression-based definition of the early stages of follicular development. Normal fetal and postnatal ovarian tissue is defined by the presence of follicular structures and characteristic immunohistochemical staining patterns, including granulosa cells expressing Forkhead Box Protein L2 (FOXL2). However, the current standard array of immunohistochemical markers poorly defines ovarian stromal tissue, and additional work is needed to identify new markers to advance our ability to accurately identify ovarian stromal components in gonadal specimens from patients with disorders of sexual differentiation.

Endometriosis and nuclear receptors

BACKGROUND

Endometriosis is recognized as a steroid-dependent disorder; however, the precise roles of nuclear receptors (NRs) in steroid responsiveness and other signaling pathways are not well understood.

OBJECTIVE AND RATIONALE

Over the past several years, a number of paradigm-shifting breakthroughs have occurred in the area of NRs in endometriosis. We review and clarify new information regarding the mechanisms responsible for: (i) excessive estrogen biosynthesis, (ii) estrogen-dependent inflammation, (iii) defective differentiation due to progesterone resistance and (iv) enhanced survival due to deficient retinoid production and action in endometriosis. We emphasize the roles of the relevant NRs critical for these pathological processes in endometriosis.

SEARCH METHODS

We conducted a comprehensive search using PubMed for human, animal and cellular studies published until 2018 in the following areas: endometriosis; the steroid and orphan NRs, estrogen receptors alpha (ESR1) and beta (ESR2), progesterone receptor (PGR), steroidogenic factor-1 (NR5A1) and chicken ovalbumin upstream promoter-transcription factor II (NR2F2); and retinoids.

OUTCOMES

Four distinct abnormalities in the intracavitary endometrium and extra-uterine endometriotic tissue underlie endometriosis progression: dysregulated differentiation of endometrial mesenchymal cells, abnormal epigenetic marks, inflammation activated by excess estrogen and the development of progesterone resistance. Endometriotic stromal cells compose the bulk of the lesions and demonstrate widespread epigenetic abnormalities. Endometriotic stromal cells also display a wide range of abnormal NR expression. The orphan NRs NR5A1 and NR2F2 compete to regulate steroid-synthesizing genes in endometriotic stromal cells; NR5A1 dominance gives rise to excessive estrogen formation. Endometriotic stromal cells show an abnormally low ESR1:ESR2 ratio due to excessive levels of ESR2, which mediates an estrogen-driven inflammatory process and prostaglandin formation. These cells are also deficient in PGR, leading to progesterone resistance and defective retinoid synthesis. The pattern of NR expression, involving low ESR1 and PGR and high ESR2, is reminiscent of uterine leiomyoma stem cells. This led us to speculate that endometriotic stromal cells may display stem cell characteristics found in other uterine tissues. The biologic consequences of these abnormalities in endometriotic tissue include intense inflammation, defective differentiation and enhanced survival.

WIDER IMPLICATIONS

Steroid- and other NR-related abnormalities exert genome-wide biologic effects via interaction with defective epigenetic programming and enhance inflammation in endometriotic stromal cells. New synthetic ligands, targeting PGR, retinoic acid receptors and ESR2, may offer novel treatment options.

Developmental Programming: Prenatal Testosterone Excess on Ovarian SF1/DAX1/FOXO3

Prenatal testosterone (T) excess, partly via androgenic programming, enhances follicular recruitment/persistence in sheep as in women with polycystic ovarian syndrome (PCOS). Decreased anti-Mullerian hormone (AMH) in early growing and increased AMH in antral follicles may underlie enhanced recruitment and persistence, respectively. Changes in AMH may be mediated by steroidogenic factor 1 (SF1), an enhancer of AMH, and dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1 (DAX1), that antagonizes SF1. Another mediator could be forkhead box 03 (FOXO3) which regulates follicular recruitment/atresia. To test if androgen-programmed changes in SF1, DAX1, and FOXO3 proteins contribute to follicular defects in prenatal T-treated sheep, ovaries from control, prenatal T-, and dihydrotestosterone (DHT)-treated (days 30-90 of gestation) animals at fetal day (FD) 90, FD140, and 1 and 2 years-of-age were studied. Prenatal T increased DAX1 in granulosa cells of primordial through large preantral and theca cells of large preantral follicles at FD140 and increased SF1 in the granulosa cells of preantral and antral and theca cells of large preantral follicle at 2 years-of-age. Prenatal T increased FOXO3 only in theca cells of preantral (FD140) and antral (2 years-of-age) follicles. Prenatal DHT increased DAX1 in granulosa cells from small preantral follicles at FD140 while increasing SF1 in granulosa cells from antral follicles at 1 year-of-age. These age-dependent changes in DAX1/SF1 partly via androgen-programming are consistent with changes in AMH and may contribute to the enhanced follicular recruitment/persistence, and multifollicular phenotype of prenatal T-treated females and may be of translational relevance to PCOS.

Signaling through non-membrane nuclear phosphoinositide binding proteins in human health and disease

Phosphoinositide membrane signaling is critical for normal physiology, playing well-known roles in diverse human pathologies. The basic mechanisms governing phosphoinositide signaling within the nucleus, however, have remained deeply enigmatic owing to their presence outside the nuclear membranes. Over 40% of nuclear phosphoinositides can exist in this non-membrane state, held soluble in the nucleoplasm by nuclear proteins that remain largely unidentified. Recently, two nuclear proteins responsible for solubilizing phosphoinositides were identified, steroidogenic factor-1 (SF-1; NR5A1) and liver receptor homolog-1 (LRH-1; NR5A2), along with two enzymes that directly remodel these phosphoinositide/protein complexes, phosphatase and tensin homolog (PTEN; MMAC) and inositol polyphosphate multikinase (IPMK; ipk2). These new footholds now permit the assignment of physiological functions for nuclear phosphoinositides in human diseases, such as endometriosis, nonalcoholic fatty liver disease/steatohepatitis, glioblastoma, and hepatocellular carcinoma. The unique nature of nuclear phosphoinositide signaling affords extraordinary clinical opportunities for new biomarkers, diagnostics, and therapeutics. Thus, phosphoinositide biology within the nucleus may represent the next generation of low-hanging fruit for new drugs, not unlike what has occurred for membrane phosphatidylinositol 3-kinase drug development. This review connects recent basic science discoveries in nuclear phosphoinositide signaling to clinical pathologies, with the hope of inspiring development of new therapies.

NR5A1 mutations are not associated with male infertility in Indian men

NR5A1 or steroidogenic factor 1 (SF1) is an autosomal gene, which encodes a protein that is a member of nuclear receptor family. NR5A1 regulates the transcription of numerous genes that are expressed in hypothalamic-pituitary-gonadal axis and adrenal cortex which in turn, coordinate the gonadal development, steroidogenesis and sex differentiation. Several mutations in NR5A1 have been reported to cause gonadal dysgenesis with adrenal insufficiency in individuals with 46,XY karyotype. However, studies in the past few years have shown that NR5A1 mutations can also contribute to primary ovarian insufficiency and impaired spermatogenesis. As there is no genetic study on NR5A1 in Indian infertile men, we have sequenced the entire coding region (exons 2-7) of NR5A1 in 502 infertile men of which, 414 were non-obstructive azoospermic and 88 severe oligozoospermic, along with 427 ethnically matched fertile controls. Interestingly, none of the mutations reported to be associated with male infertility were found in our study, except one polymorphism, rs1110061. However, it was not significantly different between infertile and fertile groups (p = .76). In addition, we have identified six intronic variants; but none of them was significantly associated with male infertility.

Steroid hormone synthesis by the ovarian stroma surrounding epithelial ovarian tumors: a potential mechanism in ovarian tumorigenesis

Epithelial ovarian tumors are responsive to steroid hormone stimulation and the ovarian stroma may have a direct role in this process. We evaluated immunohistochemical markers of sex-steroid differentiation and steroidogenesis (calretinin, inhibin, steroidogenic factor 1), steroid enzymes involved in hormone biosynthesis (CYP17, CYP19, HSD17β1, AKR1C3), and hormone receptors (estrogen receptor, progesterone receptor, and androgen receptor) in 101 epithelial ovarian tumors and in normal structures implicated in ovarian carcinogenesis (ovarian surface epithelium and cortical inclusion cysts) in an attempt to elucidate this process. We hypothesized that ovarian stroma immediately adjacent to tumors express markers of sex-steroid differentiation and steroidogenesis and steroid enzymes whereas the epithelium contains corresponding hormone receptors. As the findings in seromucinous, endometrioid, and clear cell neoplasms, tumors closely associated with endometriosis, were very similar, these were combined into a group designated 'endometriosis-related tumors.' Significantly increased expression of markers of sex-steroid differentiation and steroidogenesis was found in stroma immediately adjacent to endometriosis-related tumors (P=0.003) and mucinous tumors (primary and metastatic mucinous tumors were combined because of similar findings) (P<0.0001) compared with more remote ovarian stroma. In addition, sex-steroid enzymes were increased in stroma adjacent to endometriosis-related tumors (P=0.02) and mucinous tumors (P=0.02) compared with more distant stroma. Steroid hormone receptors showed greater expression in epithelium compared with stroma in the endometriosis-related tumors (P=0.0009), low-grade serous tumors (P<0.0001), and high-grade serous carcinoma (P=0.0036). In contrast, there was greater expression in stroma compared with epithelium (P<0.0001) in mucinous tumors, which may be due to the fact that they are not derived from müllerian epithelium. In conclusion, our findings strongly support the view that the stroma surrounding epithelial tumors in the ovary is activated to elaborate steroid hormones which may stimulate further neoplastic growth. The precise mechanisms by which this process might occur are complex and require further investigation.

Adrenomedullin2 (ADM2)/intermedin (IMD) in rat ovary: changes in estrous cycle and pregnancy and its role in ovulation and steroidogenesis

Adrenomedullin2 (ADM2) is reported to facilitate embryo implantation and placental development. Therefore, the current study was undertaken to identify if ADM2 has a functional role in ovary to facilitate its reproductive actions. This study shows that the expression of ADM2 is differentially regulated in rat estrous cycle and that ADM2 increases the synthesis and secretion of 17beta-estradiol accompanied with an increase in the expression of steroidogenic factor 1 (Sf1), estrogen receptor Esr1, and enzymes involved in steroidogenesis in equine chorionic gonadotropin (eCG)-treated rat ovaries. In addition, inhibition of endogenous ADM2 function in eCG-treated immature rats caused impaired ovulation. Furthermore, the mRNA expression of Adm2 and receptor activity modifying protein 3 is higher in the ovary on Day 18 compared to nonpregnant and pregnant rats on Day 22. ADM2-like immunoreactivity is localized in granulosa cells, blood vessels, oocytes, cumulous oophorus, and corpus luteum of pregnant ovaries, suggesting a potential role for ADM2 in the ovary. This is supported by the presence of ADM2-like immunoreactivity in the corpus luteum during pregnancy and a decline in aromatase immunoreactivity in corpus luteum on Day 9 of gestation in rats infused with ADM2 antagonist during implantation and decidualization phase. Taken together, this study suggests a potential involvement of ADM2 in the rat ovary in regulating synthesis of estradiol to support ovulation and facilitate efficient implantation and placental development for a successful pregnancy.

Lhcgr Expression in Granulosa Cells: Roles for PKA-Phosphorylated β-Catenin, TCF3, and FOXO1

Ovarian follicles lacking FSH or FSH receptors fail to progress to a preovulatory stage, resulting in infertility. One hallmark of the preovulatory follicle is the presence of luteinizing hormone/choriogonadotropin receptors (LHCGR) on granulosa cells (GCs). However, the mechanisms by which FSH induces Lhcgr gene expression are poorly understood. Our results show that protein kinase A (PKA) and phosphoinositide 3-kinase (PI3K)/AKT pathways are required for FSH to activate both the murine Lhcgr-luciferase reporter and expression of Lhcgr mRNA in rat GCs. Based on results showing that an adenovirus (Ad) expressing a steroidogenic factor 1 (SF1) mutant that cannot bind β-catenin abolished FSH-induced Lhcgr mRNA, we evaluated the role of β-catenin in the regulation of Lhcgr gene expression. FSH promoted the PKA-dependent, PI3K-independent phosphorylation of β-catenin on Ser552 and Ser665. FSH activated the β-catenin/T-cell factor (TCF) artificial promoter-reporter TOPFlash via a PKA-dependent, PI3K-independent pathway, and dominant-negative (DN) TCF abolished FSH-activated Lhcgr-luciferase reporter and induction of Lhcgr mRNA. Microarray analysis of GCs treated with Ad-DN-TCF and FSH identified the Lhcgr as the most down-regulated gene. Chromatin immunoprecipitation results placed β-catenin phosphorylated on Ser552 and Ser675 and SF1 on the Lhcgr promoter in FSH-treated GCs; TCF3 was constitutively associated with the Lhcgr promoter. Transduction with an Ad-phospho-β-catenin mutant (Ser552/665/Asp) enhanced Lhcgr mRNA expression in FSH-treated cells greater than 3-fold. Finally, we identified a recognized PI3K/AKT target, forkhead box O1, as a negative regulator of Lhcgr mRNA expression. These results provide new understanding of the complex regulation of Lhcgr gene expression in GCs.

Involvement of estrogen receptor beta in the induction of polyovular follicles in mouse ovaries exposed neonatally to diethylstilbestrol

Natural and synthetic estrogens, Including diethylstilbestrol (DES), given during the critical period of newborn life Induce abnormalities in ovaries of mice. Induction of polyovular follicles (PFs) containing two or more oocytes in a follicle is one example. In this study, the involvement of estrogen receptor subtypes ERalpha and ERbeta in induction of PFs by neonatal treatment with DES was analyzed by using ERalpha knockout (alphaERKO) and ERbeta knockout (betaERKO) mice. Ovaries of mice injected with 3 microg DES for 5 days from the day of birth were examined histologically from 10 to 60 days of age, and the expression of genes involved in folliculogenesis was analyzed by real-time quantitative PCR. The PF Incidence (percent of PFs per 100 follicles greater than 50 microm in diameter) in the ovary of alphaERKO mice treated with DES was not different from that in the DES-treated wild-type mice. However, neonatal DES treatment did not increase the PF incidence in betaERKO mice, suggesting that PFs were induced by DES through ERbeta but not ERalpha. The expression of bone morphogenetic protein 15, growth differentiation factor 9, inhibin-alpha, Müllerian inhibiting substance, and other genes in the ovaries of DES-treated betaERKO mice was not different from that in the ovaries of DES-treated wild-type mice. These results indicate that ERbeta but not ERalpha is essential for DES to Induce PFs in mice.

Molecular aspects of steroidogenic factor 1 (SF-1)

Steroidogenic factor 1 (SF-1, also called Ad4BP and NR5A1) is a nuclear receptor with critical roles in steroidogenic tissues, as well as in the brain and pituitary. In particular, SF-1 has emerged as an essential regulator of adrenal and gonadal functions and development. In the last few years, our knowledge on SF-1 has increased considerably at all levels, from the gene to the protein, and on its specific roles in different physiological processes. In this review, we discuss the current understanding on SF-1 with focus on the parameters that control the transcriptional capacity of SF-1 and the mechanisms that ensure proper stage- and tissue-specific expression of the gene encoding SF-1.

Boys, girls and shuttling of SRY and SOX9

In the mammalian embryo, SRY and SOX9 are key Sertoli cell proteins that drive the development of the bipotential gonad into a testes rather than an ovary, leading ultimately to the male phenotype. Clinical SRY and SOX9 mutations causing disorders of sex development (DSD) highlight defective protein-protein interactions between SRY or SOX9, and carrier proteins required for nuclear import (importin-b and calmodulin) and nuclear export (CRM-1). The fine balance between import and export determines the levels of transcriptionally active SRY and SOX9 in the nucleus. Recently, post-translational modifications of SRY and SOX9 have been identified which affect nuclear transport. It is therefore timely that the consequences of sex-reversal mutation upon nuclear transport be reviewed. SRY and SOX9 mutations in DSD have uncovered regulatory sites for sumoylation, ubiquitination, acetylation and phosphorylation, many of which are essential for their transport and sex determining functions.

The promoter of the oocyte-specific gene, Gdf9, is active in population of cultured mouse embryonic stem cells with an oocyte-like phenotype

The study of germ cell-specific gene regulation in vitro is challenging. Here we report that the promoter of the oocyte-specific gene, Gdf9, is active in a population of cultured murine embryonic stem cells (ES) which have a phenotype resembling oocytes. The promoter region of the murine Gdf9 coupled to enhanced green fluorescent protein (eGFP) was stably transfected into XX mouse ES cells. eGFP was expressed only in oocytes of chimeric mice generated from the transfected XX ES cells. The transfected ES cells were examined when cultured on feeder layers or as embryoid bodies. Large eGFP-positive cells, surrounded by a structure resembling a zona pellucida appeared transiently in cultures of the ES cells on feeder layers. Surprisingly, they were detectable on days 1 and 2 of culture but virtually absent on day 3. Addition of leukemia inhibitory factor (LIF) to the media significantly increased the number of eGFP-positive cels resembling oocytes. Quantitative-time PCR demonstrated a parallel increase in Gdf9 and Zp3 mRNA with changes in the abundance of eGFP-positive cells. In embryoid body cultures, eGFP-positive cells appeared transiently and then re-appeared in regional clusters after 30-45 days of culture. These findings demonstrate that a population of cultured murine ES cells contain the transcriptional machinery to drive expression of an oocyte-specific gene, and that those cells phenotypically resemble oocytes.

Ovarian follicle development and transgenic mouse models

Ovarian follicle development is a complex process that begins with the establishment of what is thought to be a finite pool of primordial follicles and culminates in either the atretic degradation of the follicle or the release of a mature oocyte for fertilization. This review highlights the many advances made in understanding these events using transgenic mouse models. Specifically, this review describes the ovarian phenotypes of mice with genetic mutations that affect ovarian differentiation, primordial follicle formation, follicular growth, atresia, ovulation and corpus luteum (CL) formation. In addition, this review describes the phenotypes of mice with mutations in a variety of genes, which affect the hormones that regulate folliculogenesis. Because studies using transgenic animals have revealed a variety of reproductive abnormalities that resemble many reproductive disorders in women, it is likely that studies using transgenic mouse models will impact our understanding of ovarian function and fertility in women.

Cyclic AMP-dependent modification of gonad-selective TAF(II)105 in a human ovarian granulosa cell line

In response to gonadotropins, the elevated level of intracellular-cyclic AMP (cAMP) in ovarian granulosa cells triggers an ordered activation of multiple ovarian genes, which in turn promotes various ovarian functions including folliculogenesis and steroidogenesis. Identification and characterization of transcription factors that control ovarian gene expression are pivotal to the understanding of the molecular basis of the tissue-specific gene regulation programs. The recent discovery of the mouse TATA binding protein (TBP)-associated factor 105 (TAF(II)105) as a gonad-selective transcriptional co-activator strongly suggests that general transcription factors such as TFIID may play a key role in regulating tissue-specific gene expression. Here we show that the human TAF(II)105 protein is preferentially expressed in ovarian granulosa cells. We also identified a novel TAF(II)105 mRNA isoform that results from alternative exon inclusion and is predicted to encode a dominant negative mutant of TAF(II)105. Following stimulation by the adenylyl cyclase activator forskolin, TAF(II)105 in granulosa cells undergoes rapid and transient phosphorylation that is dependent upon protein kinase A (PKA). Thus, our work suggests that pre-mRNA processing and post-translational modification represent two important regulatory steps for the gonad-specific functions of human TAF(II)105.

Expression of Sox8, Sf1, Gata4, Wt1, Dax1, and Fog2 in the mouse ovarian follicle: implications for the regulation of Amh expression

Anti-Mullerian hormone (Amh) is expressed in the granulosa cells of growing and preovulatory follicles in the mouse ovary where it acts to decrease responsiveness to follicle stimulating hormone (FSH) and plays a role in inhibiting primordial follicle recruitment. Recently, co-culture of isolated oocytes and granulosa cells has demonstrated that Amh expression is up-regulated in the presence of oocytes and, at preantral stages, this effect is dependent upon close contact. In Sertoli cells, Amh expression is regulated by several transcription factors including SOX9, SF1, GATA4, WT1, and DAX1, which, with the exception of SOX9, are also expressed in granulosa cells where GATA4 is known to up-regulate Amh expression antagonised by FOG2. Here, we demonstrate that Sox8, which is closely related to Sox9 and encodes the protein SOX8 which can transactivate Amh, is expressed in the postnatal mouse ovarian follicle but is not co-expressed with Amh in the granulosa cells of preantral follicles. Sox8 expression was found only in the oocytes of preantral follicles and in the oocytes, cumulus cells, and mural granulosa cells of preovulatory follicles. Also, increased expression of Amh in granulosa cells co-cultured with oocytes was not associated with increased mRNA levels of the transcription factors Sf1, Gata4, Wt1, Dax1, or Fog2. These findings reveal Sox8 expression in the ovarian follicle and show that oocyte regulation of Amh expression is not due to oocyte regulation of Sf1, Gata4, Wt1, Dax1, or Fog2 expression in granulosa cells.

Molecular biology of gonadotropin-releasing hormone (GnRH)-I, GnRH-II, and their receptors in humans

In human beings, two forms of GnRH, termed GnRH-I and GnRH-II, encoded by separate genes have been identified. Although these hormones share comparable cDNA and genomic structures, their tissue distribution and regulation of gene expression are significantly dissimilar. The actions of GnRH are mediated by the GnRH receptor, which belongs to a member of the rhodopsin-like G protein-coupled receptor superfamily. However, to date, only one conventional GnRH receptor subtype (type I GnRH receptor) uniquely lacking a carboxyl-terminal tail has been found in the human body. Studies on the transcriptional regulation of the human GnRH receptor gene have indicated that tissue-specific gene expression is mediated by differential promoter usage in various cell types. Functionally, there is growing evidence showing that both GnRH-I and GnRH-II are potentially important autocrine and/or paracrine regulators in some extrapituitary compartments. Recent cloning of a second GnRH receptor subtype (type II GnRH receptor) in nonhuman primates revealed that it is structurally and functionally distinct from the mammalian type I receptor. However, the human type II receptor gene homolog carries a frameshift and a premature stop codon, suggesting that a full-length type II receptor does not exist in humans.

Generation and characterization of human steroidogenic factor 1 LBD crystals with and without bound cofactor peptide

The nuclear receptor Steroidogenic Factor 1 (SF1) plays a critical role in the development of the adrenal gland and gonads, and in sexual differentiation. SF1 performs this pivotal function through the regulation of hormone expression that is essential for organogenesis and endocrine homeostasis. SF1 is a member of a nuclear receptor subclass that contains LRH1 and the Drosophila receptor FTZ-F1. To date, a natural ligand has not been reported for any member of this subfamily. Here we report the crystallization and characterization of the ligand-binding domain (LBD) of human SF1 from two different crystal forms: a binary complex with fortuitous ligand and a ternary complex with the same ligand and a peptide containing a motif of a nuclear receptor cofactor. The structural determination of the binary complex required the use of sulfur SAD phasing, a relatively new technique that uses anomalous diffraction from the endogenous sulfur atoms present in the protein. The structure of the ternary complex was determined by multiple wavelength anomalous diffraction (MAD) using seleno-methionine substituted SF1. Preliminary analysis suggested SF1 contained a fortuitous ligand in the binding pocket. This ligand may account for the relatively high basal activity observed for SF1 in cofactor recruitment and cell-based assays.

Regulation of transcription of the steroidogenic acute regulatory protein (StAR) gene: temporal and spatial changes in transcription factor binding and histone modification

We examined the binding of transcription factors and histone modifications associated with induction of expression of the steroidogenic acute regulatory protein (StAR) gene in MA-10 cells using a quantitative chromatin immunoprecipitation (ChIP) assay. GATA-4, SF-1/Ad4BP, and cyclic AMP response element binding protein binding protein (CBP) bind rapidly to the StAR proximal promoter, but in different patterns following 8-Br-cAMP stimulation. Concomitantly, histone modifications occur in a spatial and temporal sequence including increased association of acetylated histone H3 with the proximal promoter region, increased association of dimethylated lysine 4 histone H3 with exonic sequences, a modification that marks actively transcribed regions, and reduced association of a marker linked to gene silencing (lysine 9 dimethylated histone H3). Our findings demonstrate that transcription factors and coactivators are rapidly associated with the StAR proximal promoter, that the patterns of binding differ which has implications for postulated direct interactions among these factors, and that multiple histone modifications are demonstrable in a spatially- and temporally-specific pattern along the StAR gene. These observations suggest that a combinatorial code of transcription factors including reciprocal changes in histone modifications associated with active transcription and gene silencing control StAR gene expression.

Small nuclear RING finger protein stimulates the rat luteinizing hormone-beta promoter by interacting with Sp1 and steroidogenic factor-1 and protects from androgen suppression

GnRH controls expression of the LH subunit genes, alpha and LHbeta, with the LHbeta subunit regulated most dramatically. Two enhancer regions, distal and proximal, on the rat LHbeta gene promoter cooperate for full basal expression and GnRH stimulation. It has been hypothesized that the transcription factors binding to these regions, Sp1, Egr-1, and steroidogenic factor 1 (SF-1), may interact directly or indirectly via a coactivator. One such coactivator may be small nuclear RING finger protein (SNURF), which is expressed in pituitary tissue and the LbetaT2 gonadotrope cell line. In transfection experiments in LbetaT2 cells, SNURF stimulated basal expression of LHbeta and increased overall GnRH stimulation. SNURF specifically stimulated LHbeta, with no effect on the alpha-subunit promoter. SNURF interacts with Sp1 and SF-1, but not Egr-1, in pull-down experiments. Point mutations or deletions of SNURF functional domains demonstrated that Sp1 and SF-1 interactions with SNURF are required for SNURF stimulatory effects on the LHbeta promoter. Endogenous SNURF is associated with the LHbeta promoter on native chromatin, suggesting that it plays a physiological role in LHbeta gene expression. SNURF also binds the androgen receptor, and SNURF overexpression overcomes androgen suppression of GnRH-stimulated LHbeta but not alphasubunit promoter activity. SNURF mutations that disrupt Sp1 or SF-1 binding eliminate rescue by SNURF. We conclude that SNURF may mediate interactions between the distal and proximal GnRH response regions of the LHbeta promoter to stimulate transcription and can also protect the promoter from androgen suppression.

Regulation of alpha-fetoprotein expression by Nkx2.8

The alpha-fetoprotein (AFP) gene is an important model of developmental gene silencing and neoplastic gene reactivation. Nkx2.8 is a divergent homeodomain factor originally cloned through its binding to the promoter-coupling element (PCE), a regulatory region upstream of the AFP promoter that mediates stimulation by distant enhancers. Nkx2.8 is the only developmentally regulated factor that has been associated with AFP gene expression. Fetoprotein transcription factor, an orphan nuclear receptor, has also been shown to bind the PCE but is not developmentally regulated. The binding specificities of both families of transcription factor were determined, and overlapping sites for each were defined in the PCE. After modification of nuclear extract and gel shift analysis procedures, Nkx2.8 was identified in six AFP-positive cell lines. Transient-transfection analysis did not show transcriptional stimulation by Nkx2.8 or other active NK2 factors, which only interfered with gene expression. However, two sets of analysis demonstrated the relationship of Nkx2.8 to AFP expression: chromatin immunoprecipitation demonstrated that Nkx2.8 bound to the active AFP promoter, and antisense inhibition of Nkx2.8 mRNA translation selectively reduced expression of both the endogenous human AFP gene and transfected reporters containing the rat AFP promoter.

Retinoic acid mediates transcriptional repression of ovine follicle-stimulating hormone receptor gene via a pleiotropic nuclear receptor response element

The FSH receptor (FSHR) and retinoid receptors are critical regulators of gonadal function. Unlike the latter, the FSH receptors are expressed exclusively in ovarian granulosa and testicular Sertoli cells in a developmental fashion. Toward understanding the nature of various transcription factors that direct a tissue- and stage-specific expression of the FSHR gene, we have studied FP4, one of the two footprinting regions (FP3 and FP4) mapped at -241 to -269 and -284 to -303, respectively, upstream of the transcription start site of the ovine FSHR gene. Gel mobility shift assays with FP4 probe revealed two sequence-specific DNA-protein complexes in the presence of nuclear extracts from two immortal gonadal cell lines. Antibody supershift assays demonstrated that retinoic acid receptor (RAR) was involved in the complex 1 whereas steroidogenic factor-1 (SF-1) was present in the complex 2. Mutation studies revealed that DNA binding sites for RAR and SF-1 were overlapping each other within a 19-base pair length of nucleotide sequence of FP4, and a mutation in the half RAR binding site seriously affected SF-1 binding. Reporter assays showed that FP4 conferred SF-1 transactivation as well as RAR-mediated, ligand-dependent repression. Overexpression of SF-1 in a transformed Sertoli cell line partially overcame RAR-mediated suppression. For the first time, our studies reveal a direct retinoid modulation of the gonadotropin receptor promoter and suggest a mechanism by which activators and repressors compete for composite elements providing antagonistic pathways that could modulate the expression of FSHR.

Origins of follicular cells and ontogeny of steroidogenesis in ovine fetal ovaries

Using fetal sheep as the experimental model, we have elucidated some of the key events that culminate in the formation of primordial follicles. A special effort was made to determine the source of the somatic cells that ultimately become granulosa cells of primordial follicles. Between gestational days 38-100: (1) light and electron microscopy was used to characterize changes in ovarian histoarchitecture; (2) incorporation of BrdU was used to identify populations of proliferating cells within fetal ovaries before, during and after, follicular formation; and (3) in situ hybridisation was used to determine the cell-specific and temporal patterns of expression of mRNAs encoding for selected steroidogenic enzymes. At day 38 somatic (pregranulosa) cells were in contact with oogonia and easily distinguished from endothelial and mesenchymal cells. Between days 38 and 45, pregranulosa cell-oogonia complexes progressively coalesced to form 'tube-like' structures referred to as ovigerous cords. These cords consisted of pregranulosa cells and oogonia arranged such that pregranulosa cells formed the outer wall of the cords. Ovigerous cords were avascular, enveloped in a prominent basal lamina, open-ended where they interfaced with the ovarian surface epithelium, and formed a separate compartment whereby oogonia/oocytes were segregated from the surrounding stroma and vasculature until the time of follicular formation. The structural integrity of ovigerous cords was maintained through day 75, at which time primordial follicles (type 1 and type 1a) first emerged from the cords at the interface of the cortex and medulla. On the basis of the sequential structural changes that occurred during the differentiation and development of fetal ovaries and location of proliferating cells identified by the incorporation of BrdU, we conclude that the majority of the granulosa cells in primordial follicles are derived from mesothelial cells originating from the ovarian surface epithelium. In addition, from the cell-specific distribution and temporal pattern of expression of mRNAs for key steroidogenic enzymes we hypothesize that steroid hormones may play a pivotal paracrine/autocrine role in the formation and/or function of ovigerous cords as well as the development of the ovarian vascular network.

Increased expression of Müllerian-inhibiting substance correlates with inhibition of follicular growth in the developing ovary of rats treated with E2 benzoate

Müllerian-inhibiting substance (MIS) is an essential factor for male sexual differentiation. In the present study, we examined whether the expression of MIS and several of its related transcription factors is altered in the ovaries of rats treated with the synthetic estrogen, E2 benzoate (EB; 10 microg/0.02 ml), from postnatal day 1 (P1) to P5. The EB-treated rats had a significantly reduced number of layered follicles at P6 in comparison with the control rats that were treated with vehicle alone. The expression levels of both MIS mRNA and protein in the granulosa cells of small growing follicles in the ovary at P6 were higher in the EB-treated rats than in the controls. These results indicate that the inhibitory effect of EB on the follicular stratification may correlate with the inappropriately increased expression level of MIS. Furthermore, the expression levels of one of its transcriptional activators, steroidogenic factor 1, and ER-beta in granulosa cells of small growing follicles were higher in EB-treated ovaries than in the control ovaries. These results suggest the role of MIS in the regulation of follicular growth and the possible involvement of steroidogenic factor 1 and/or ER-beta in this molecular cascade may contribute to postnatal ovarian development.

Identification of porcine Lhx3 and SF1 as candidate genes for QTL affecting growth and reproduction traits in swine

The distal portion of the long arm of porcine chromosome 1 has been shown to harbour several quantitative trait loci affecting growth and reproductive traits in swine. In order to identify potential candidate genes that might underlie these effects, a comparative mapping analysis was undertaken to define the extent of orthologous segments of human chromosome 9. A microsatellite associated with heat shock protein (HSP) A5 was used to define the proximal boundary of the quantitative trait loci (QTL) region, which suggests the human orthologue of the gene(s) responsible for the observed effects lies between HSPA5 and the q arm telomere of human chromosome 9. Examination of this region revealed two candidate genes with known roles in production of hormones essential to growth and reproductive function. The steroidogenic factor 1 and Lhx3 LIM homeodomain transcription factor genes were mapped to 123 and 155 cM, respectively, of the Sus scrofa chromosome 1 (SSC1) linkage group, placing both genes within the confidence interval for the observed QTL. To further evaluate Lhx3, we examined the expression profile during porcine embryonic development. Low levels were detected at early embryonic stages, when development of the nervous system is proceeding. A transient increase in expression level is observed during the time of pituitary organogenesis and again at the time of differentiation of anterior pituitary cells, with relatively high levels of expression persisting in the adult pituitary gland. This ontology is consistent with Lhx3 being a candidate gene for the QTL.

The nuclear receptor Ftz-F1 and homeodomain protein Ftz interact through evolutionarily conserved protein domains

The Drosophila homeodomain protein Fushi Tarazu (Ftz) and its partner, the orphan receptor Ftz-F1, are members of two distinct families of DNA binding transcriptional regulators. Ftz and Ftz-F1 form a novel partnership in vivo as a Hox/orphan receptor heterodimer. Here we show that the murine Ftz-F1 ortholog SF-1 functionally substitutes for Ftz-F1 in vivo, rescuing the defects of ftz-f1 mutants. This finding identified evolutionarily conserved domains of Ftz-F1 as critical for activity of this receptor in vivo. These domains function, at least in part, by mediating direct protein interactions with Ftz. The Ftz-F1 DNA binding domain interacts strongly with Ftz and dramatically facilitates the binding of Ftz to target DNA. This interaction is augmented by a second interaction between the AF-2 domain of Ftz-F1 and the N-terminus of Ftz via an LRALL sequence in Ftz that is reminiscent of LXXLL motifs in nuclear receptor coactivators. We propose that Ftz-F1 serves as a cofactor for Ftz by facilitating the selection of target sites in the genome that contain Ftz/Ftz-F1 composite binding sites. Ftz, on the other hand, influences Ftz-F1 activity by interacting with its AF-2 domain in a manner that mimics a nuclear receptor coactivator.

Neonatal estrogen exposure inhibits steroidogenesis in the developing rat ovary

Treatment of newborn female rats with estrogens significantly inhibits the growth and differentiation of the ovary. To understand the molecular mechanism of estrogen action in the induction of abnormal ovary, we examined the expression profiles of steroidogenic factor 1 (SF-1) and several of its target genes in the developing ovaries after neonatal exposure to synthetic estrogen, estradiol benzoate (EB) by using reverse transcriptase polymerase chain reaction, in situ hybridization, and immunohistochemistry. Morphologic examination indicated inhibitory effects of estrogen on the stratification of follicles and development of theca and interstitial gland during postnatal ovarian differentiation. The expression of the steroidogenic acute regulatory protein (StAR) and cholesterol side-chain cleavage cytochrome P450 (P450(SCC)), which are both essential for steroid biosynthesis, markedly decreased in theca and interstitial cells throughout the postnatal development of the EB-treated ovary. However, expression of the transcriptional activator of the two genes, SF-1 was unaffected in theca and interstitial cells, although the number of these cells was lower in the EB-treated ovary than in the control ovary. The expression of the estrogen mediator, estrogen receptor-alpha (ER-alpha), diminished specifically in theca cells at P6 and recovered by P14 in the EB-treated ovary. These results indicate that the effect of estrogens is mediated by means of ER-alpha resulting in the down-regulation of StAR and P450(SCC) genes during early postnatal development of the ovary. These results suggest that the abnormal ovarian development by neonatal estrogen treatment is closely correlated with the reduced steroidogenic activity, and the data obtained by using this animal model may account in part the mechanism for aberrant development and function of the ovary in prenatally estrogen-exposed humans.