Murine relaxin-like factor promoter: functional characterization and regulation by transcription factors steroidogenic factor 1 and DAX-1

Clinical features and underlying mechanisms of KAT6B disease in a Chinese boy

BACKGROUND

Lysine acetyltransferase 6B (KAT6B) encodes a highly conserved histone acetyltransferase that regulates the expression of multiple genes and is essential for human growth and development.

METHODS

We identified a novel frameshift variant c.3185del (p.leu1062Argfs*52) in a 5-year-old Chinese boy and further analyzed KAT6B expression and its interacting complexes and downstream products using real-time quantitative polymerase chain reaction (qPCR). Furthermore, we assessed its three-dimensional protein structure and compared the variant with other reported KAT6B variants.

RESULTS

The deletion changed the leucine at position 1062 into an arginine, resulting in translation termination after base 3340, which may have affected protein stability and protein-protein interactions. KAT6B mRNA expression levels in this case were substantially different from those of the parents and controls in the same age range. There were also significant differences in mRNA expression levels among affected children's parents. RUNX2 and NR5A1, downstream products of the gene, affect the corresponding clinical symptoms. The mRNA expression levels of the two in children were lower than those of their parents and controls in the same age range.

CONCLUSION

This deletion in KAT6B may affect protein function and cause corresponding clinical symptoms through interactions with key complexes and downstream products.

A 35-bp Conserved Region Is Crucial for Insl3 Promoter Activity in Mouse MA-10 Leydig Cells

The peptide hormone insulin-like 3 (INSL3) is produced almost exclusively by Leydig cells of the male gonad. INSL3 has several functions such as fetal testis descent and bone metabolism in adults. Insl3 gene expression in Leydig cells is not hormonally regulated but rather is constitutively expressed. The regulatory region of the Insl3 gene has been described in various species; moreover, functional studies have revealed that the Insl3 promoter is regulated by various transcription factors that include the nuclear receptors AR, NUR77, COUP-TFII, LRH1, and SF1, as well as the Krüppel-like factor KLF6. However, these transcription factors are also found in several tissues that do not express Insl3, indicating that other, yet unidentified factors, must be involved to drive Insl3 expression specifically in Leydig cells. Through a fine functional promoter analysis, we have identified a 35-bp region that is responsible for conferring 70% of the activity of the mouse Insl3 promoter in Leydig cells. All tri- and dinucleotide mutations introduced dramatically reduced Insl3 promoter activity, indicating that the entire 35-bp sequence is required. Nuclear proteins from MA-10 Leydig cells bound specifically to the 35-bp region. The 35-bp sequence contains GC- and GA-rich motifs as well as potential binding elements for members of the CREB, C/EBP, AP1, AP2, and NF-κB families. The Insl3 promoter was indeed activated 2-fold by NF-κB p50 but not by other transcription factors tested. These results help to further define the regulation of Insl3 gene transcription in Leydig cells.

Retinoic Acid Antagonizes Testis Development in Mice

Mammalian sex determination depends on a complex interplay of signals that promote the bipotential fetal gonad to develop as either a testis or an ovary, but the details are incompletely understood. Here, we investigated whether removal of the signaling molecule retinoic acid (RA) by the degradative enzyme CYP26B1 is necessary for proper development of somatic cells of the testes. Gonadal organ culture experiments suggested that RA promotes expression of some ovarian markers and suppresses expression of some testicular markers, acting downstream of Sox9. XY Cyp26b1-null embryos, in which endogenous RA is not degraded, develop mild ovotestes, but more important, steroidogenesis is impaired and the reproductive tract feminized. Experiments involving purified gonadal cells showed that these effects are independent of germ cells and suggest the direct involvement of the orphan nuclear receptor DAX1. Our results reveal that active removal of endogenous RA is required for normal testis development in the mouse.

Leydig cell stem cells: Identification, proliferation and differentiation

Adult Leydig cells develop from undifferentiated mesenchymal-like stem cells (stem Leydig cells, SLCs) present in the interstitial compartment of the early postnatal testis. Putative SLCs also have been identified in peritubular and perivascular locations of the adult testis. The latter cells, which normally are quiescent, are capable of regenerating new Leydig cells upon the loss of the adult cells. Recent studies have identified several protein markers to identify these cells, including nestin, PDGFRα, COUP-TFII, CD51 and CD90. We have shown that the proliferation of the SLCs is stimulated by DHH, FGF2, PDGFBB, activin and PDGFAA. Suppression of proliferation occurred with TGFβ, androgen and PKA signaling. The differentiation of the SLCs into testosterone-producing Leydig cells was found to be regulated positively by DHH (Desert hedgehog), lithium-induced signaling and activin; and negatively by TGFβ, PDGFBB, FGF2, Notch and Wnt signaling. DHH, by itself, was found to induce SLC differentiation into LH-responsive steroidogenic cells, suggesting that DHH plays a critical role in the commitment of SLC into the Leydig lineage. These studies, taken together, address the function and regulation of low turnover stem cells in a complex, adult organ, and also have potential application to the treatment of androgen deficiency.

Mutational screening of NR5A1 gene encoding steroidogenic factor 1 in cryptorchidism and male factor infertility and functional analysis of seven undescribed mutations

OBJECTIVE

To study the role of NR5A1 in cryptorchidism and male factor infertility. Mutations in NR5A1 have been initially associated with primary adrenal insufficiency and 46,XY gonadal dysgenesis and more recently with less severe phenotypes, including preliminary descriptions in severe forms of male factor infertility. Far less clear is the possible involvement of NR5A1 mutations in cryptorchidism.

DESIGN

Retrospective cross-sectional cohort study and functional analysis of mutant proteins.

SETTING

University department.

PATIENT(S)

Nine hundred fifty-nine subjects, including children with cryptorchidism and adults with different semen phenotypes associated or not associated with a history of cryptorchidism.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Mutation screening of NR5A1 by sequencing all exons. Functional analysis of mutant proteins by transactivation assays of CYP11A1 and CYP17A1 promoters.

RESULT(S)

We identified seven undescribed and one previously described missense mutation in subjects with severe spermatogenic impairment, without (4/236, 1.7%) and with (3/85, 3.5%) a history of cryptorchidism. Newborns with cryptorchidism carry NR5A1 mutations at low frequency (0.7%), whereas no mutations were found in milder forms of infertility and normozoospermia, irrespective of the presence of cryptorchidism. The mutant proteins showed impaired transactivation of gonadal promoters. A single nucleotide polymorphism (rs1110061; c.437 G→C; p.Gly146Ala) was also associated with more severe forms of spermatogenic impairment with cryptorchidism.

CONCLUSION(S)

This study, combined with what is already known about NR5A1-associated phenotypes, suggests considering mutations in this gene as a novel genetic cause of more severe forms of male factor infertility, especially when associated with a history of cryptorchidism.

Insulin-like 3-induced rat preantral follicular growth is mediated by growth differentiation factor 9

The communication of somatic cells and oocytes by intrafollicular paracrine factors is essential for follicular growth in the ovary. Insulin-like 3 (INSL3) is a theca cell-secreted paracrine factor. Androgens and growth differentiation factor 9 (GDF9), an oocyte-derived growth factor, are essential for follicular development. Using a rat preantral follicle culture model, we examined in the present study the influence of INSL3 on preantral follicular growth and the molecular mechanisms involved. We have observed that the receptor for INSL3, relaxin/insulin-like family peptide receptor 2 (RXFP2), was exclusively expressed in oocytes. Recombinant INSL3 stimulated Gdf9 expression, preantral follicular growth, and testosterone synthesis in vitro. Inhibition of the cAMP/protein kinase A signaling pathway (with cAMP antagonist, 8-bromoadenosine 3',5'-cyclic monophosphorothioate, Rp-isomer) attenuated INSL3-induced Gdf9 expression and preantral follicular growth. Moreover, knocking down Gdf9 expression (with small interfering RNA) or inhibiting GDF9 signaling (with SB431542, an activin receptor-like kinase receptor 5 inhibitor, or specific inhibitor of mothers against decapentaplegic homolog 3) or androgen action (with flutamide, an androgen receptor antagonist) suppressed INSL3-induced preantral follicular growth. In addition, LH and DHT regulated the expression of Insl3 mRNA in preantral follicles. These observations suggest that INSL3 is a key theca cell-derived growth factor for preantral follicle and that its action is mediated by GDF9.

Excess DAX1 leads to XY ovotesticular disorder of sex development (DSD) in mice by inhibiting steroidogenic factor-1 (SF1) activation of the testis enhancer of SRY-box-9 (Sox9)

Human DAX1 duplications cause dosage-sensitive sex reversal (DSS) whereby chromosomally XY individuals can develop as females due to gonadal dysgenesis. However, the mechanism of DSS-adrenal hypoplasia congenita on X, gene 1 (DAX1) action in the fetal testis is unknown. We show that in fetal testes from XY Dax1-overexpressing transgenic mice, the expression of the key testis-promoting gene sex-determining region on Y (SRY)-box-9 (Sox9) is reduced. Moreover, in XY Sox9 heterozygotes, in which testis development is usually normal, Dax1 overexpression results in ovotestes, suggesting a DAX1-SOX9 antagonism. The ovarian portion of the XY ovotestes was characterized by expression of the granulosa cell marker, Forkhead box-L2, with complete loss of the Sertoli cell markers, SOX9 and anti-Müllerian hormone, and the Leydig cell marker CYP17A1. However, the expression of SRY and steroidogenic factor-1 (SF1), two key transcriptional regulators of Sox9, was retained in the ovarian portion of the XY ovotestes. Using reporter mice, Dax1 overexpression reduced activation of TES, the testis enhancer of Sox9, indicating that DAX1 might repress Sox9 expression via TES. In cultured cells, increasing levels of DAX1 antagonized SF1-, SF1/SRY-, and SF1/SOX9-mediated activation of TES, due to reduced binding of SF1 to TES, providing a likely mechanism for DSS.

Fetal Leydig cells: progenitor cell maintenance and differentiation

In most eutherian mammals, sexually dimorphic masculinization is established by androgen-producing fetal Leydig cells in the embryonic testis. Fetal Leydig cells, which lack expression of the testis-determining gene SRY, arise after the appearance of SRY-expressing Sertoli cells. Therefore, the appearance and differentiation of fetal Leydig cells are probably regulated by factors derived from Sertoli cells. Results from mouse genetic models have revealed that maintenance and differentiation of fetal Leydig cell population depends upon a balance between differentiation-promoting and differentiation-suppressing mechanisms. Although paracrine signaling via Sertoli cell-derived Hedgehog ligands is necessary and sufficient for fetal Leydig cell formation, cell-cell interaction via Notch signaling and intracellular transcription factors such as POD1 are implicated as suppressors of fetal Leydig cell differentiation. This review provides a model that summarizes the recent findings in fetal Leydig cell development.

Nuclear receptors, testosterone, and posttranslational modifications in human INSL3 promoter activity in testicular Leydig cells

Insulin-like peptide 3 (INSL3) is a hormone produced by fetal and adult Leydig cells of the mammalian testis. During embryonic life INSL3 is required for testicular descent, whereas in adults it is involved in bone metabolism and male germ cell survival. Despite these important roles, the molecular mechanisms regulating INSL3 expression remain poorly understood. So far, two transcription factors have been implicated in INSL3 transcription: the nuclear receptors SF1 and NUR77. Circumstantial evidence also points to a role for androgens. Using transient transfections in MA-10 Leydig cells, we found that testosterone regulates in a time- and dose-dependent manner the human INSL3 promoter. The INSL3 promoter, however, does not contain a classical androgen-responsive element. Testosterone responsiveness was found to be mediated through an element located in the proximal INSL3 promoter, which also contains a NUR77-SF1-binding site. Furthermore, we found that posttranslational modifications, such as phosphorylation and acetylation, modulate transcription factor activity and therefore also contribute to INSL3 promoter activity in Leydig cells. All together, these data provide new insights into the molecular mechanisms regulating INSL3 expression in the mammalian testis.

INSL3/RXFP2 signaling in testicular descent

Mutations of the insulin-like peptide 3 (INSL3) hormone or its receptor, RXFP2, cause intraabdominal cryptorchidism in male mice. Specific RXFP2 expression in mouse gubernacula was detected at embryonic day 14.5 and markedly increased after birth in the developing cremaster muscle, as well as in the epididymis and testicular Leydig and germ cells. INSL3 treatment stimulated cell proliferation of embryonic gubernacular and Leydig cells, implicating active INSL3-mediated signaling. The transcription factor SOX9, a known male sex determination factor, upregulated the activity of the RXFP2 promoter. INSL3 is sufficient to direct the first transabdominal phase of testicular descent in the absence of hypothalamic-pituitary-gonadal axis signaling or Hoxa10, although these factors are important for inguinoscrotal testicular descent. Similarly, conditional ablation of the androgen receptor gene in gubernacular cells resulted in disruption of inguinoscrotal descent. We performed mutation screening of INSL3 and RXFP2 in human patients with cryptorchidism and control subjects from different populations in Europe and the USA. Several missense mutations were described in both the INSL3 and RXFP2 genes. A novel V39G INSL3 mutation in a patient with cryptorchidism was identified; however, the functional analysis of the mutant peptide did not reveal compromised function. In more than 2000 patients and controls analyzed to date, the T222P RXFP2 mutation is the only one strongly associated with the mutant phenotype. The T222P mutant receptor, when transfected into 293T cells, had severely decreased cell membrane expression, providing the basis for the functional deficiency of this mutation.

Activation of the Hedgehog pathway in the mouse fetal ovary leads to ectopic appearance of fetal Leydig cells and female pseudohermaphroditism

Proper cell fate determination in mammalian gonads is critical for the establishment of sexual identity. The Hedgehog (Hh) pathway has been implicated in cell fate decision for various organs, including gonads. Desert Hedgehog (Dhh), one of the three mammalian Hh genes, has been implicated with other genes in the establishment of mouse fetal Leydig cells. To investigate whether Hh alone is sufficient to induce fetal Leydig cell differentiation, we ectopically activated the Hh pathway in Steroidogenic factor 1 (SF1)-positive somatic cell precursors of fetal ovaries. Hh activation transformed SF1-positive somatic ovarian cells into functional fetal Leydig cells. These ectopic fetal Leydig cells produced androgens and insulin-like growth factor 3 (INLS3) that cause virilization of female embryos and ovarian descent. However, the female reproductive system remained intact, indicating a typical example of female pseudohermaphroditism. The appearance of fetal Leydig cells was a direct consequence of Hh activation as evident by the absence of other testicular components in the affected ovary. This study provides not only insights into mechanisms of cell lineage specification in gonads, but also a model to understand defects in sexual differentiation.

Relaxin and related peptides in male reproduction

The relaxin hormone is renowned for its function in pregnancy, parturition and other aspects of female reproduction. At the same time, the role of relaxin in male reproduction is still debated. Relaxin is prominently expressed in prostate and its receptors are found in several male reproductive organs; however, the data indicative of its contribution to differentiation and functioning of prostate or testis are contradictory. Prostate relaxin is a main source of this peptide in the seminal plasma. The relaxin effects on sperm motility and fertilization have been reported. The expression of other relaxin related peptides, such as INSL5 and INSL6 was described in testis; yet, currently there are no experimental data to pinpoint their biological functions. The other member of relaxin peptide family, insulin-like 3 peptide (INSL3), is a major player in male development. The INSL3 peptide is expressed in testicular fetal and adult Leydig cells and is directly responsible for the process of abdominal testicular descent (migration of the testes towards the scrotum during male development). Genetic targeting of the Insl3 gene or INSL3 GPCR receptor Lgr8/Rxfp2 causes high intra-abdominal cryptorchidism due to a differentiation failure of testicular ligaments, the gubernacula. Several mutations of these two genes rendering nonfunctional proteins have been described in human patients with testicular maldescent. Thus, in this chapter we review the data related to the expression and function of relaxin and related peptides in male reproduction.

Antagonistic effects of testosterone and the endocrine disruptor mono-(2-ethylhexyl) phthalate on INSL3 transcription in Leydig cells

Insulin-like 3 (INSL3) is a small peptide produced by testicular Leydig cells throughout embryonic and postnatal life and by theca and luteal cells of the adult ovary. During fetal life, INSL3 regulates testicular descent in males, whereas in adults, it acts as an antiapoptotic factor for germ cells in males and as a follicle selection and survival factor in females. Despite its considerable roles in the reproductive system, the mechanisms that regulate Insl3 expression remain poorly understood. There is accumulating evidence suggesting that androgens might regulate Insl3 expression in Leydig cells, but transcriptional data are still lacking. We now report that testosterone does increase Insl3 mRNA levels in a Leydig cell line and primary Leydig cells. We also show that testosterone activates the activity of the Insl3 promoter from different species. In addition, the testosterone-stimulating effects on Insl3 mRNA levels and promoter activity require the androgen receptor. We have mapped the testosterone-responsive element to the proximal Insl3 promoter region. This region, however, lacks a consensus androgen response element, suggesting an indirect mechanism of action. Finally we show that mono-(2-ethylhexyl) phthalate, a widely distributed endocrine disruptor with antiandrogenic activity previously shown to inhibit Insl3 expression in vivo, represses Insl3 transcription, at least in part, by antagonizing testosterone/androgen receptor action. All together our data provide important new insights into the regulation of Insl3 transcription in Leydig cells and the mode of action of phthalates.

Estrogen receptor alpha is a major contributor to estrogen-mediated fetal testis dysgenesis and cryptorchidism

Failure of the testes to descend into the scrotum (cryptorchidism) is one of the most common birth defects in humans. In utero exposure to estrogens, such as 17beta-estradiol (E2) or the synthetic estrogen diethylstilbestrol (DES), down-regulates insulin-like 3 (Insl3) expression in embryonic Leydig cells, which in turn results in cryptorchidism in mice. To identify the molecular mechanism whereby xenoestrogens block Insl3 gene transcription, we performed a microarray analysis of wild-type or estrogen receptor (ER) alpha-mutant testes exposed in utero to pharmacological doses of E2 or DES. Six and 31 genes were respectively down-regulated and up-regulated by estrogen exposure (> or =4-fold). All six genes down-regulated by estrogen exposure, including Insl3 and the steroidogenic genes steroidogenic acute regulatory protein and cytochrome P450 17alpha-hydroxylase/17,20-lyase, were done so by an ERalpha-dependent mechanism. In contrast, up-regulation was mediated either by ERalpha for 12 genes or by an independent mechanism for the 19 remaining genes. Finally, we show that Insl3 gene expression and testicular descent were not affected by in utero exposure to E2 or DES in ERalpha mutant mice, whereas absence of ERbeta did not influence the effect of these estrogens. Collectively, these data demonstrate that xenoestrogens inhibit the endocrine functions of fetal Leydig cells through an ERalpha-dependent mechanism.

Developmental Expression and Gene Regulation of Insulin-like 3 Receptor RXFP2 in Mouse Male Reproductive Organs1

The mutations of testicular insulin-like 3 (INSL3) hormone or its receptor RXFP2 cause cryptorchidism in male mice. Here we have examined Rxfp2 gene expression at different stages of embryonic and postnatal mouse development in male reproductive tissues employing quantitative RT-PCR and several RXFP2-specific antibodies directed toward different parts of the RXFP2 protein. Receptor expression was markedly increased after birth and was readily detectable in the epididymis, Leydig cells, and germ cells of the testis. The strongest expression was detected in adult mouse cremaster muscle. INSL3 treatment increased cell proliferation of embryonic gubernacular and TM3 embryonic Leydig cells, implicating active INSL3-mediated autocrine signaling in these cells and identifying TM3 as a novel in vitro model to study the effects of RXFP2 signaling. We generated Tg(Rxfp2-cre)Aia (Rxfp2-iCre) transgenic mice expressing improved Cre recombinase (iCre) under the control of the 2.4-kb mouse Rxfp2 promoter. The iCre was expressed in the gubernacular ligament at E14.5, indicating that this promoter is able to drive Rxfp2 gene expression during transabdominal testis descent. We demonstrated that the transcription factor Sox9, a known male sex determination factor, is expressed in mouse embryonic gubernacula and upregulated human, but not mouse, promoter luciferase reporter constructs. In conclusion, we have determined the developmental expression profile of INSL3 receptor employing newly characterized RXFP2 antisera and a novel Rxfp2-iCre transgenic mouse model. We determined the promoter region capable of providing the gubernacular-specific expression of Rxfp2. Analysis of RXFP2 promoter identified SOX9 as a new transcriptional enhancer of human gene expression.

Heterozygous missense mutations in steroidogenic factor 1 (SF1/Ad4BP, NR5A1) are associated with 46,XY disorders of sex development with normal adrenal function

CONTEXT

Steroidogenic factor 1 (SF1/AdBP4/FTZF1, NR5A1) is a nuclear receptor transcription factor that plays a key role in regulating adrenal and gonadal development, steroidogenesis, and reproduction. Targeted deletion of Nr5a1 (Sf1) in the mouse results in adrenal and gonadal agenesis, XY sex-reversal, and persistent Müllerian structures in males. Consistent with the murine phenotype, human mutations in SF1 were described initially in two 46,XY individuals with female external genitalia, Müllerian structures (uterus), and primary adrenal failure.

OBJECTIVE

Given recent case reports of haploinsufficiency of SF1 affecting testicular function in humans, we aimed to identify SF1 mutations in a cohort of individuals with a phenotypic spectrum of 46,XY gonadal dysgenesis/impaired androgenization (now termed 46,XY disorders of sex development) with normal adrenal function.

METHODS AND PATIENTS

The study included mutational analysis of NR5A1 in 30 individuals with 46,XY disorders of sex development, followed by functional studies of SF1 activity.

RESULTS

Heterozygous missense mutations in NR5A1 were found in four individuals (four of 30, 13%) with this phenotype. These mutations (V15M, M78I, G91S, L437Q) were shown to impair transcriptional activation through abnormal DNA binding (V15M, M78I, G91S), altered subnuclear localization (V15M, M78I), or disruption of the putative ligand-binding pocket (L437Q). Two mutations appeared to be de novo or germline changes. The other two mutations appeared to be inherited in a sex-limited dominant manner because the mother is heterozygous for the change.

CONCLUSIONS

These studies demonstrate that SF1 mutations are more frequent than previously suspected causes of impaired fetal and postnatal testicular function in 46,XY individuals.

Paracrine and endocrine roles of insulin-like factor 3

Insulin-like factor 3 (INSL3) is expressed in Leydig cells of the testis and theca cells of the ovary. This peptide affects testicular descent by acting on gubernaculum via its specific receptor leucine-rich repeat-containing G protein-coupled receptor 8 (LGR8). From initial animal data showing the cryptorchid phenotype of Insl3/Lgr8 mutants, an extensive search for mutations in INSL3 and LGR8 genes was undertaken in human patients with cryptorchidism, and a frequency of mutation of 4-5% has been detected. However, definitive proofs of a causative role for some of these mutations are still lacking. More recent data suggest additional paracrine (in the testis and ovary) and endocrine actions of INSL3 in adults. INSL3 circulates at high concentrations in serum of adult males and its production is dependent on the differentiation effect of LH. Therefore, INSL3 is increasingly used as a specific marker of Leydig cell differentiation and function.

Mechanisms underlying the anti-androgenic effects of diethylhexyl phthalate in fetal rat testis

Diethylhexyl phthalate (DEHP) is widely used as a plasticizer in consumer products and is known to disturb the development of the male reproductive system in rats. The mechanisms by which DEHP exerts these effects are not yet fully elucidated, though some of the effects are related to reduced fetal testosterone production. The present study investigated the effects of four different doses of DEHP on fetal testicular histopathology, testosterone production and expression of proteins and genes involved in steroid synthesis in fetal testes. Pregnant Wistar rats were gavaged from GD 7 to 21 with vehicle, 10, 30, 100 or 300 mg/kg bw/day of DEHP. In male fetuses examined at GD 21, testicular testosterone production ex vivo and testicular testosterone levels were reduced significantly at the highest dose. Histopathological effects on gonocytes were observed at 100 and 300 mg/kg bw/day, whereas Leydig cell effects were mainly seen at 300 mg/kg bw/day. Quantitative RT-PCR revealed reduced testicular mRNA expression of the steroidogenesis related factors SR-B1, StAR, PBR and P450scc. Additionally, we observed reduced mRNA expression of the nuclear receptor SF-1, which regulates certain steps in steroid synthesis, and reduced expression of the cryptorchidism-associated Insl-3. Immunohistochemistry showed clear reductions of StAR, PBR, P450scc and PPARgamma protein levels in fetal Leydig cells, indicating that DEHP affects regulation of certain steps in cholesterol transport and steroid synthesis. The suppression of testosterone levels observed in phthalate-exposed fetal rats was likely caused by the low expression of these receptors and enzymes involved in steroidogenesis. It is conceivable that the observed effects of DEHP on the expression of nuclear receptors SF-1 and PPARgamma are involved in the downregulation of steroidogenic factors and testosterone levels and thereby underlie the disturbed development of the male reproductive system.

Orphan nuclear receptor Nur77 induces zinc finger protein GIOT-1 gene expression, and GIOT-1 acts as a novel corepressor of orphan nuclear receptor SF-1 via recruitment of HDAC2

Kruppel-associated box (KRAB) domain-containing proteins consist of potential transcriptional repression modules. Previously, gonadotropin-inducible ovarian transcription factor-1 (GIOT-1) was identified as a novel KRAB-containing zinc finger protein and shown to have transcriptional repression activity. Here, we demonstrate that orphan nuclear receptor Nur77 regulates GIOT-1 gene expression in testicular Leydig cell lines and that GIOT-1 acts as a novel corepressor of the orphan nuclear receptor steroidogenic factor 1 (SF-1). Mutation analysis of the GIOT-1 promoter and overexpression analysis of dominant-negative Nur77 revealed that luteinizing hormone activates GIOT-1 gene expression through Nur77. Electrophoretic mobility shift and chromatin immunoprecipitation assays showed that Nur77 directly binds to the GIOT-1 promoter. GIOT-1 represses the SF-1 transactivation, and specific interaction between GIOT-1 and SF-1 was observed. We also demonstrate an interaction between GIOT-1 and histone deacetylase 2 (HDAC2). GIOT-1-mediated transrepression was recovered by down-regulation of HDAC2 expression with small interfering RNA of HDAC2. Knock down of the endogenous GIOT-1 results in significant enhancement of CYP17 expression in Leydig cells. In conclusion, this study of cross-talk between GIOT-1 and orphan nuclear receptors will provide new insights into the role of KRAB-containing zinc finger proteins in nuclear receptor action.

Insulin-Like Factor 3: Where Are We Now?

Insulin-like factor 3 (INSL3), previously known as the relaxin-like factor (RLF), is a major peptide hormone secreted from the testicular Leydig cells of adult men and circulating in the blood at a concentration of approximately 1 ng/mL. Women also produce INSL3 in the theca interna cells of ovarian follicles, but circulating levels remain below 100 pg/mL. INSL3 is structurally related to relaxin and insulin, but unlike the latter, signals through a novel G-protein-coupled receptor, LGR8. Ablation of the gene for INSL3 leads primarily to cryptorchidism because of a defect in the first, transabdominal phase of testicular descent. In the adult knockout mouse, a mild phenotype is evident in the testis and ovary. We have developed a panel of antibodies specific for INSL3 from various species, which are suitable for immunohistochemistry and, more recently, for immunoassays. INSL3 is an important marker for the mature Leydig cell phenotype, where it appears to be expressed constitutively, once the mature differentiation state is achieved. It is also an indicator of differentiation status not only for Leydig cells but also for the theca interna cells of the ovary.

The orphan nuclear receptor NR4A1 regulates insulin-like 3 gene transcription in Leydig cells

Insulin-like 3 (INSL3) is a hormone produced by fetal and adult Leydig cells of the testis and by theca and luteal cells of the adult ovary. In males, INSL3 regulates testicular descent during fetal life, whereas in adults, it acts as a germ cell survival factor. In the ovary, INSL3 regulates oocyte maturation. Despite its importance for male sex differentiation and reproductive function in both sexes, very little is known regarding the molecular mechanisms that regulate Insl3 expression. So far, the nuclear receptor NR5A1 is the only transcription factor known to regulate the mouse Insl3 promoter in Leydig cells. NR5A1 by itself, however, cannot explain the spatiotemporal expression pattern of the Insl3 gene. In the present study, we have identified the orphan nuclear receptor NR4A1 as a novel regulator of INSL3 transcription in Leydig cells. Using RT-PCR, we found that Nr4a1 is coexpressed with Insl3 in purified Leydig cells and in several Leydig cell lines. Through detailed analyses of the mouse and human INSL3 promoter in Leydig cells, we have mapped a novel regulatory element located at -100 bp that is essential and sufficient to confer NR4A1 responsiveness. Consistent with a role for NR4A1 in Insl3 transcription, chromatin immunoprecipitation assays revealed that endogenous NR4A1 binds to the proximal Insl3 promoter in vivo. Finally, we found that NR4A1 is also implicated in cAMP-induced Insl3 transcription in Leydig cells. Taken together, our identification of NR4A1 as an important regulator of mouse and human INSL3 promoter activity helps us to better define the tissue-specific regulation of the INSL3 gene in gonadal cells.

Isolation and expression analysis of the canine insulin-like factor 3 gene

The insulin-like factor 3 (INSL3 or relaxin-like factor) is a hormone produced mainly in gonadal tissues in males and females. Deletion of INSL3 or its receptor in male mice leads to the undescended testes, or cryptorchidism. Here we describe an isolation and analysis of full-length canine INSL3 gene. The INSL3 gene is composed of two exons within a small genomic region. Putative translation of the isolated cDNA yields 132 amino acid preproINSL3 that has the domain structure characteristic for the insulin-relaxin peptide superfamily with a well-conserved receptor-binding domain. Northern blot hybridization showed stronger expression of INSL3 in testis than in ovary. Reverse transcription-polymerase chain reaction analysis of the INSL3 expression revealed a minor splice variant of INSL3 potentially encoding 105 amino acids peptide. We established that the medium, conditioned with recombinant canine INSL3, produced from the full-length cDNA, but not from the minor splice variant, activated human GREAT/LGR8 receptor in vitro. In addition to the functional allele of INSL3, genomic DNA of one of the analyzed dogs contained an intronless nonexpressed pseudogene of INSL3. We isolated canine INSL3 promoter and showed that its activity was strongly mediated by steroidogenic factor-1 in vitro. Using site-specific mutagenesis, we identified a well-conserved steroidogenic factor-1 binding site within canine INSL3 promoter.

SF-1 a key player in the development and differentiation of steroidogenic tissues

Since its discovery in the early 1990s, the orphan nuclear receptor SF-1 has been attributed a central role in the development and differentiation of steroidogenic tissues. SF-1 controls the expression of all the steroidogenic enzymes and cholesterol transporters required for steroidogenesis as well as the expression of steroidogenesis-stimulating hormones and their cognate receptors. SF-1 is also an essential regulator of genes involved in the sex determination cascade. The study of SF-1 null mice and of human mutants has been of great value to demonstrate the essential role of this factor in vivo, although the complete adrenal and gonadal agenesis in knock-out animals has impeded studies of its function as a transcriptional regulator. In particular, the role of SF-1 in the hormonal responsiveness of steroidogenic genes promoters is still a subject of debate. This extensive review takes into account recent data obtained from SF-1 haploinsufficient mice, pituitary-specific knock-outs and from transgenic mice experiments carried out with SF-1 target gene promoters. It also summarizes the pros and cons regarding the presumed role of SF-1 in cAMP signalling.

DAX-1, an unusual orphan receptor at the crossroads of steroidogenic function and sexual differentiation

The unusual orphan member of the nuclear hormone receptor superfamily DAX-1 (NR0B1) owes its name to its double role in human pathology. On one side, duplications in Xp21, containing the DAX-1 gene, cause phenotypic sex reversal in XY individuals. On the other side, DAX-1 gene mutations are responsible for adrenal hypoplasia congenita, invariably associated with hypogonadotropic hypogonadism. DAX-1 functions as a global negative regulator of steroid hormone production by repressing the expression of multiple genes involved in the steroidogenic pathway. Here we review the mechanism of DAX-1 function in adrenal and gonadal differentiation, with special emphasis on recent results showing the critical role of DAX-1 protein misfolding in the pathogenesis of adrenal hypoplasia congenita.