Identification of a putative steroidogenic factor-1 response element in the DAX-1 promoter

Intronic Enhancer Is Essential for Nr5a1 Expression in the Pituitary Gonadotrope and for Postnatal Development of Male Reproductive Organs in a Mouse Model

Nuclear receptor subfamily 5 group A member 1 (NR5A1) is expressed in the pituitary gonadotrope and regulates their differentiation. Although several regulatory regions were implicated in Nr5a1 gene expression in the pituitary gland, none of these regions have been verified using mouse models. Furthermore, the molecular functions of NR5A1 in the pituitary gonadotrope have not been fully elucidated. In the present study, we generated mice lacking the pituitary enhancer located in the 6th intron of the Nr5a1 gene. These mice showed pituitary gland-specific disappearance of NR5A1, confirming the functional importance of the enhancer. Enhancer-deleted male mice demonstrated no defects at fetal stages. Meanwhile, androgen production decreased markedly in adult, and postnatal development of reproductive organs, such as the seminal vesicle, prostate, and penis was severely impaired. We further performed transcriptomic analyses of the whole pituitary gland of the enhancer-deleted mice and controls, as well as gonadotropes isolated from Ad4BP-BAC-EGFP mice. These analyses identified several genes showing gonadotrope-specific, NR5A1-dependent expressions, such as Spp1, Tgfbr3l, Grem1, and Nr0b2. These factors are thought to function downstream of NR5A1 and play important roles in reproductive organ development through regulation of pituitary gonadotrope functions.

Gonadal Transcriptome Analysis and Sequence Characterization of Sex-Related Genes in Cranoglanis bouderius

In China, the Cranoglanis bouderius is classified as a national class II-protected animal. The development of C. bouderius populations has been affected by a variety of factors over the past few decades, with severe declines occurring. Considering the likelihood of continued population declines of the C. bouderius in the future, it is critical to investigate the currently unknown characteristics of gonadal differentiation and sex-related genes for C. bouderius conservation. In this study, the Illumina sequencing platform was used to sequence the gonadal transcriptome of the C. bouderius to identify the pathways and genes related to gonadal development and analyze the expression differences in the gonads. A total of 12,002 DEGs were identified, with 7220 being significantly expressed in the ovary and 4782 being significantly expressed in the testis. According to the functional enrichment results, the cell cycle, RNA transport, apoptosis, Wnt signaling pathway, p53 signaling pathway, and prolactin signaling pathway play important roles in sex development in the C. bouderius. Furthermore, the sequence characterization and evolutionary analysis revealed that AMH, DAX1, NANOS1, and AR of the C. bouderius are highly conserved. Specifically, the qRT-PCR results from various tissues showed significant differences in AMH, DAX1, NANOS1, and AR expression levels in the gonads of both sexes of C. bouderius. These analyses indicated that AMH, DAX1, NANOS1, and AR may play important roles in the differentiation and development of C. bouderius gonads. To our best knowledge, this study is the first to analyze the C. bouderius gonadal transcriptome and identify the structures of sex-related genes, laying the foundation for future research.

Steroidogenic Factor 1 (NR5A1) Activates ATF3 Transcriptional Activity

Steroidogenic Factor 1 (SF-1/NR5A1), an orphan nuclear receptor, is important for sexual differentiation and the development of multiple endocrine organs, as well as cell proliferation in cancer cells. Activating transcription factor 3 (ATF3) is a transcriptional repressor, and its expression is rapidly induced by DNA damage and oncogenic stimuli. Since both NR5A1 and ATF3 can regulate and cooperate with several transcription factors, we hypothesized that NR5A1 may interact with ATF3 and plays a functional role in cancer development. First, we found that NR5A1 physically interacts with ATF3. We further demonstrated that ATF3 expression is up-regulated by NR5A1. Moreover, the promoter activity of the ATF3 is activated by NR5A1 in a dose-dependent manner in several cell lines. By mapping the ATF3 promoter as well as the site-directed mutagenesis analysis, we provide evidence that NR5A1 response elements (-695 bp and -665 bp) are required for ATF3 expression by NR5A1. It is well known that the transcriptional activities of NR5A1 are modulated by post-translational modifications, such as small ubiquitin-related modifier (SUMO) modification and phosphorylation. Notably, we found that both SUMOylation and phosphorylation of NR5A1 play roles, at least in part, for NR5A1-mediated ATF3 expression. Overall, our results provide the first evidence of a novel relationship between NR5A1 and ATF3.

Expression and regulation of GnRHR2 gene and testosterone secretion mediated by GnRH2 and GnRHR2 within porcine testes

Gonadotropin-releasing hormone 2 receptor (GnRHR2) together with its cognate ligand involves in regulating reproductive behavior. However, little is known concerning the effect of transcription factor steroidogenic factor1 (SF-1) regulation on porcine GnRHR2 gene expression and GnRH2 regulation mechanism in testosterone secretion through GnRHR2. Our study demonstrated that GnRHR2 transcription levels were high in porcine testis. Immunohistochemistry analyses showed that GnRHR2 immunoreactivity was strong in the Leydig cells in boar testes. Two SF-1 binding sites were predicted in GnRHR2 promoter and the second site (-159/-149) was considered to be important for GnRHR2 promoter activity through site-directed mutagenesis. The binding of SF-1 to GnRHR2 promoter was confirmed by electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP). Overexpression and knockdown experiments revealed that SF-1 could up-regulate porcine GnRHR2 expression. DNA methylation of GnRHR2 promoter CpG island also specifically regulated GnRHR2 expression. Meanwhile, our study also demonstrated GnRH2 treatment promoted the expression of SF-1 and steroidogenic acute regulatory protein (StAR), and that this treatment stimulated cAMP responsive element binding protein (CREB) phosphorylation, regulated the expression of GnRHR2, especially that of GnRHR2-X1, and promoted testosterone secretion in porcine Leydig cells. We speculated that testosterone secretion mediated by GnRH2 and GnRHR2 (mainly GnRHR2-X1) was regulated by phosphorylated CREB interacting with SF-1 to control StAR expression. Taken together, the present study indicates that SF-1 and GnRH2 are the essential regulatory factors for GnRHR2 expression. This study also explores the regulation mechanism of testosterone secretion mediated by GnRH2 and GnRHR2 in porcine Leydig cells.

Role of Orphan Nuclear Receptor DAX-1/NR0B1 in Development, Physiology, and Disease

DAX-1/NR0B1 is an unusual orphan receptor that has a pivotal role in the development and function of steroidogenic tissues and of the reproductive axis. Recent studies have also indicated that this transcription factor has an important function in stem cell biology and in several types of cancer. Here I critically review the most important findings on the role of DAX-1 in development, physiology, and disease of endocrine tissues since the cloning of its gene twenty years ago.

Ligand-independent actions of the orphan receptors/corepressors DAX-1 and SHP in metabolism, reproduction and disease

DAX-1 and SHP are two closely related atypical orphan members of the nuclear receptor (NR) family that make up the NR0B subfamily. They combine properties of typical NRs and of NR-associated coregulators: both carry the characteristic NR ligand-binding domain but instead of a NR DNA-binding domain they have unique N-terminal regions that contain LxxLL-related NR-binding motifs often found in coregulators. Recent structural data indicate that DAX-1 lacks a ligand-binding pocket and thus should rely on ligand-independent mechanisms of regulation. This might be true, but remains to be proven, for SHP as well. DAX-1 and SHP have in common that they act as transcriptional corepressors of cholesterol metabolism pathways that are related on a molecular level. However, the expression patterns of the two NRs are largely different, with some notable exceptions, and so are the physiological processes they regulate. DAX-1 is mainly involved in steroidogenesis and reproductive development, while SHP plays major roles in maintaining cholesterol and glucose homeostasis. This review highlights the key similarities and differences between DAX-1 and SHP with regard to structure, function and biology and considers what can be learnt from recent research advances in the field. This article is part of a Special Issue entitled 'Orphan Receptors'.

Mammalian sex determination—insights from humans and mice

Disorders of sex development (DSD) are congenital conditions in which the development of chromosomal, gonadal, or anatomical sex is atypical. Many of the genes required for gonad development have been identified by analysis of DSD patients. However, the use of knockout and transgenic mouse strains have contributed enormously to the study of gonad gene function and interactions within the development network. Although the genetic basis of mammalian sex determination and differentiation has advanced considerably in recent years, a majority of 46,XY gonadal dysgenesis patients still cannot be provided with an accurate diagnosis. Some of these unexplained DSD cases may be due to mutations in novel DSD genes or genomic rearrangements affecting regulatory regions that lead to atypical gene expression. Here, we review our current knowledge of mammalian sex determination drawing on insights from human DSD patients and mouse models.

X-linked congenital adrenal hypoplasia with hypogonadotropic hypogonadism caused by an inversion disrupting a conserved noncoding element upstream of the NR0B1 (DAX1) gene

CONTEXT

X-linked congenital adrenal hypoplasia with hypogonadotropic hypogonadism (AHCH) is known to be caused by coding mutations in the nuclear receptor subfamily 0, group B, member 1 (NR0B1) gene, encoding the transcriptional repressor dosage-sensitive sex-reversal adrenal hypoplasia critical region on the X chromosome protein 1 (DAX1).

OBJECTIVE/PATIENTS

Four males in a family were affected by AHCH. Our aim was to locate the genetic cause of their disease, knowing that they had no mutation in the obvious candidate gene, NR0B1.

DESIGN

Linkage analysis of the X chromosome and mutational screening of conserved noncoding regions upstream of NR0B1 were performed. To functionally characterize the genetic defect, studies of transcription and expression of DAX1 and steroidogenic factor 1 (SF-1) were done.

RESULTS

A 60 Mb inversion on the X chromosome with one of the inversion breakpoints located in a conserved noncoding region 4 kb upstream of NR0B1 was detected. The inversion causes relocation of a putative SF-1 binding site implicated in murine gonadal development. A reporter construct lacking this enhancer element upstream of NR0B1 was unresponsive to SF-1 transcriptional activation. Immunohistochemistry suggested that the inversion leads to SF-1 silencing in the patients' testes both in childhood and in adult life.

CONCLUSION

We report a noncoding mutation causing AHCH, an inversion resulting in a phenotype similar to what is caused by intragenic NR0B1 null mutations. The inversion seems to disrupt and/or relocate regulatory sites crucial in DAX1 expression.

Transcriptional regulation of steroidogenic genes: STARD1, CYP11A1 and HSD3B

Expression of the genes that mediate the first steps in steroidogenesis, the steroidogenic acute regulatory protein (STARD1), the cholesterol side-chain cleavage enzyme, cytochrome P450scc (CYP11A1) and 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (HSD3B), is tightly controlled by a battery of transcription factors in the adrenal cortex, the gonads and the placenta. These genes generally respond to the same hormones that stimulate steroid production through common pathways such as cAMP signaling and common actions on their promoters by proteins such as NR5A and GATA family members. However, there are distinct temporal, tissue and species-specific differences in expression between the genes that are defined by combinatorial regulation and unique promoter elements. This review will provide an overview of the hormonal and transcriptional regulation of the STARD1, CYP11A1 and specific steroidogenic HSD3B genes in the adrenal, testis, ovary and placenta and discuss the current knowledge regarding the key transcriptional factors involved.

Differential effects of high and low steroidogenic factor-1 expression on CYP11B2 expression and aldosterone production in adrenocortical cells

Steroidogenic factor-1 (SF-1/Ad4BP/NR5A1) plays a major role in regulating steroidogenic enzymes. We have previously shown that SF-1 inhibits aldosterone synthase (CYP11B2) reporter gene activity. Herein, we used the H295R/TR/SF-1 adrenal cells that increase SF-1 in a doxycycline-dependent fashion. Cells were incubated with or without doxycycline to induce SF-1 and then treated with angiotensin II (Ang II). Aldosterone was measured by immunoassay. SF-1 mRNA was silenced by small interfering RNA (siRNA) by Nucleofector technology. mRNA levels were measured by real-time RT-PCR. Ang II treatment without doxycycline increased aldosterone production by 11.3-fold and CYP11B2 mRNA by 116-fold. Doxycycline treatment increased SF-1 mRNA levels by 3.7-fold and inhibited Ang II-induced aldosterone by 84%. Doxycycline treatment inhibited Ang II-stimulated CYP11B2 mRNA levels by 86%. Doxycycline decreased basal CYP11B2 promoter activity by 68%. Doxycycline inhibited Ang II stimulation by 85%. Ang II increased CYP21 mRNA expression by 4.6-fold, whereas doxycycline inhibited induction by 69%. In contrast, doxycycline treatment increased CYP11B1 mRNA by 1.7-fold in basal cells and increased Ang II induction by 3.6-fold. SF-1-specific siRNA significantly reduced SF-1 mRNA expression as compared with cells treated with control siRNA. SF-1 siRNA reversed doxycycline stimulation of CYP B1 and its inhibition of CYP11B2. However, in H295R/TR/SF-1 cells without doxycycline treatment, both CYP11B1 and CYP11B2 mRNAs were significantly decreased, suggesting that both enzymes require a minimal level of SF-1 for basal expression. In summary, SF-1 overexpression dramatically inhibited CYP11B2 expression and decreased aldosterone production. The opposing effects of SF-1 on CYP11B1 and CYP11B2 suggest that the regulation of SF-1 activity may play a role that determines the relative ability to produce mineralocorticoid and glucocorticoid.

Mapping of five candidate sex-determining loci in rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Rainbow trout have an XX/XY genetic mechanism of sex determination where males are the heterogametic sex. The homology of the sex-determining gene (SDG) in medaka to Dmrt1 suggested that SDGs evolve from downstream genes by gene duplication. Orthologous sequences of the major genes of the mammalian sex determination pathway have been reported in the rainbow trout but the map position for the majority of these genes has not been assigned.

RESULTS

Five loci of four candidate genes (Amh, Dax1, Dmrt1 and Sox6) were tested for linkage to the Y chromosome of rainbow trout. We exclude the role of all these loci as candidates for the primary SDG in this species. Sox6i and Sox6ii, duplicated copies of Sox6, mapped to homeologous linkage groups 10 and 18 respectively. Genotyping fishes of the OSU x Arlee mapping family for Sox6i and Sox6ii alleles indicated that Sox6i locus might be deleted in the Arlee lineage.

CONCLUSION

Additional candidate genes should be tested for their linkage to the Y chromosome. Mapping data of duplicated Sox6 loci supports previously suggested homeology between linkage groups 10 and 18. Enrichment of the rainbow trout genomic map with known gene markers allows map comparisons with other salmonids. Mapping of candidate sex-determining loci is important for analyses of potential autosomal modifiers of sex-determination in rainbow trout.

SUMOylation inhibits SF-1 activity by reducing CDK7-mediated serine 203 phosphorylation

Steroidogenic factor 1 (SF-1) is an orphan nuclear receptor selectively expressed in the adrenal cortex and gonads, where it mediates the hormonal stimulation of multiple genes involved in steroid hormone biosynthesis. SF-1 is the target of both phosphorylation and SUMOylation, but how these modifications interact or contribute to SF-1 regulation of endogenous genes remains poorly defined. We found that SF-1 is selectively SUMOylated at K194 in Y1 adrenocarcinoma cells and that although SUMOylation does not alter the subcellular localization of SF-1, the modification inhibits the ability of SF-1 to activate target genes. Notably, whereas SF-1 SUMOylation is independent of S203 phosphorylation and is unaffected by adrenocorticotropin (ACTH) treatment, loss of SUMOylation leads to enhanced SF-1 phosphorylation at serine 203. Furthermore, preventing SF-1 SUMOylation increases the mRNA and protein levels of multiple steroidogenic enzyme genes. Analysis of the StAR promoter indicates that blockade of SF-1 SUMOylation leads to an increase in overall promoter occupancy but does not alter the oscillatory recruitment dynamics in response to ACTH. Notably, we find that CDK7 binds preferentially to the SUMOylation-deficient form of SF-1 and that CDK7 inhibition reduces phosphorylation of SF-1. Based on these observations, we propose a coordinated modification model in which inhibition of SF-1-mediated transcription by SUMOylation in adrenocortical cancer cells is mediated through reduced CDK7-induced phosphorylation of SF-1.

The selective Alzheimer's disease indicator-1 gene (Seladin-1/DHCR24) is a liver X receptor target gene

The nuclear hormone receptors liver X receptor alpha (LXRalpha) and LXRbeta function as physiological receptors for oxidized cholesterol metabolites (oxysterols) and regulate several aspects of cholesterol and lipid metabolism. Seladin-1 was originally identified as a gene whose expression was down-regulated in regions of the brain associated with Alzheimer's disease. Seladin-1 has been demonstrated to be neuroprotective and was later characterized as 3beta-hydroxysterol-Delta24 reductase (DHCR24), a key enzyme in the cholesterologenic pathway. Seladin-1 has also been shown to regulate lipid raft formation. In a whole genome screen for direct LXRalpha target genes, we identified an LXRalpha occupancy site within the second intron of the Seladin-1/DHCR24 gene. We characterized a novel LXR response element within the second intron of this gene that is able to confer LXR-specific ligand responsiveness to reporter gene in both HepG2 and human embryonic kidney 293 cells. Furthermore, we found that Seladin-1/DHCR24 gene expression is significantly decreased in skin isolated from LXRbeta-null mice. Our data suggest that Seladin-1/DHCR24 is an LXR target gene and that LXR may regulate lipid raft formation.

Regulation of cholesterologenesis by the oxysterol receptor, LXRalpha

Cholesterol is required for normal cellular and physiological function, yet dysregulation of cholesterol metabolism is associated with diseases such as atherosclerosis. Cholesterol biosynthesis is regulated by end product negative feedback inhibition where the levels of sterols and oxysterols regulate the expression of cholesterologenic enzymes. Sterol regulatory element-binding protein-2 is responsive to both sterols and oxysterols and has been shown to mediate the transcriptional response of the cholesterologenic enzymes to these lipids. Here, we show that the nuclear hormone receptor for oxysterols, the liver X receptor alpha (LXRalpha), regulates cholesterol biosynthesis by directly silencing the expression of two key cholesterologenic enzymes (lanosterol 14alpha-demethylase (CYP51A1), and squalene synthase (farnesyl diphosphate farnesyl transferase 1)) via novel negative LXR DNA response elements (nLXREs) located in each of these genes. Examination of the CYP51A1 gene revealed that both the SRE and nLXRE are required for normal oxysterol-dependent repression of this gene. Thus, these data suggest that LXRalpha plays an important role in the regulation of cholesterol biosynthesis.

Regulation of human 3 alpha-hydroxysteroid dehydrogenase (AKR1C4) expression by the liver X receptor alpha

Type I human hepatic 3alpha-hydroxysteroid dehydrogenase (AKR1C4) plays a significant role in bile acid biosynthesis, steroid hormone metabolism, and xenobiotic metabolism. Utilization of a hidden Markov model for predictive modeling of nuclear hormone receptor response elements coupled with chromatin immunoprecipitation/microarray technology revealed a putative binding site in the AKR1C4 promoter for the nuclear hormone receptor known as liver X receptor alpha, (LXRalpha [NR1H3]), which is the physiological receptor for oxidized cholesterol metabolites. The putative LXRalpha response element (LXRE), identified by chromatin immunoprecipitation, was approximately 1.5 kilobase pairs upstream of the transcription start site. LXRalpha was shown to bind specifically to this LXRE and mediate transcriptional activation of the AKR1C4 gene, leading to increased AKR1C4 protein expression. These data suggest that LXRalpha may modulate the bile acid biosynthetic pathway at a unique site downstream of CYP7A1 and may also modulate the metabolism of steroid hormones and certain xenobiotics.

Reciprocal regulation of a glucocorticoid receptor-steroidogenic factor-1 transcription complex on the Dax-1 promoter by glucocorticoids and adrenocorticotropic hormone in the adrenal cortex

Numerous genes required for adrenocortical steroidogenesis are activated by the nuclear hormone receptor steroidogenic factor 1 (SF-1) (NR5A1). Dax-1 (NR0B1), another nuclear hormone receptor, represses SF-1-dependent activation. Glucocorticoid products of the adrenal cortex provide negative feedback to the production of hypothalamic CRH and pituitary ACTH. We hypothesized that glucocorticoids stimulate an intraadrenal negative feedback loop via activation of Dax-1 expression. Reporter constructs show glucocorticoid-dependent synergy between SF-1 and glucocorticoid receptor (GR) in the activation of Dax-1, which is antagonized by ACTH signaling. We map the functional glucocorticoid response element between -718 and -704 bp, required for activation by GR and synergy with SF-1. Of three SF-1 response elements, only the -128-bp SF-1 response element is required for synergy with GR. Chromatin immunoprecipitation (ChIP) assays demonstrate that dexamethasone treatment increases GR and SF-1 binding to the endogenous murine Dax-1 promoter 10- and 3.5-fold over baseline. Serial ChIP assays reveal that that GR and SF-1 are part of the same complex on the Dax-1 promoter, whereas coimmunoprecipitation assay confirms the presence of a protein complex that contains both GR and SF-1. ACTH stimulation disrupts the formation of this complex by abrogating SF-1 binding to the Dax-1 promoter, while promoting SF-1 binding to the melanocortin-2 receptor (Mc2r) and steroidogenic acute regulatory protein (StAR) promoters. Finally, dexamethasone treatment increases endogenous Dax-1 expression and concordantly decreases StAR expression. ACTH signaling antagonizes the increase in Dax-1 yet strongly activates StAR transcription. These data indicate that GR provides feedback regulation of adrenocortical steroid production through synergistic activation of Dax-1 with SF-1, which is antagonized by ACTH activation of the adrenal cortex.

Nuclear receptors Sf1 and Dax1 function cooperatively to mediate somatic cell differentiation during testis development

Mutations of orphan nuclear receptors SF1 and DAX1 each cause adrenal insufficiency and gonadal dysgenesis in humans, although the pathological features are distinct. Because Dax1 antagonizes Sf1-mediated transcription in vitro, we hypothesized that Dax1 deficiency would compensate for allelic loss of Sf1. In studies of the developing testis, expression of the fetal Leydig cell markers Cyp17 and Cyp11a1 was reduced in heterozygous Sf1-deficient mice at E13.5, consistent with dose-dependent effects of Sf1. In Sf1/Dax1 (Sf1 heterozygous and Dax1-deleted) double mutant gonads, the expression of these genes was unexpectedly reduced further,indicating that loss of Dax1 did not compensate for reduced Sf1 activity. The Sertoli cell product Dhh was reduced in Sf1 heterozygotes at E11.5, and it was undetectable in Sf1/Dax1 double mutants, indicating that Sf1 and Dax1 function cooperatively to induce Dhh expression. Similarly, Amh expression was reduced in both Sf1 and Dax1 single mutants at E11.5, and it was not rescued by the Sf1/Dax1 double mutant. By contrast, Sox9 was expressed in single and in double mutants, suggesting that various Sertoli cell genes are differentially sensitive to Sf1 and Dax1 function. Reduced expression of Dhh and Amh was transient, and was largely restored by E12.5. Similarly, there was recovery of fetal Leydig cell markers by E14.5, indicating that loss of Sf1/Dax1 delays but does not preclude fetal Leydig cell development. Thus, although Sf1 and Dax1 function as transcriptional antagonists for many target genes in vitro, they act independently or cooperatively in vivo during male gonadal development.

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.

DAX1 and its network partners: exploring complexity in development

DAX1 encoded by NR0B1, when mutated, is responsible for X-linked adrenal hypoplasia congenita (AHC). AHC is due to failure of the adrenal cortex to develop normally and is fatal if untreated. When duplicated, this gene is associated with an XY sex-reversed phenotype. DAX1 expression is present during development of the steroidogenic hypothalamic-pituitary-adrenal-gonadal (HPAG) axis and persists into adult life. Despite recognition of the crucial role for DAX1, its function remains largely undefined. The phenotypes of patients and animal models are complex and not always in agreement. Investigations using cell lines have proved difficult to interpret, possibly reflecting cell line choices and their limited characterization. We will review the efforts of our group and others to identify appropriate cell lines for optimizing ex vivo analysis of NR0B1 function throughout development. We will examine the role of DAX1 and its network partners in development of the hypothalamic-pituitary-adrenal/gonadal axis (HPAG) using a variety of different types of investigations, including those in model organisms. This network analysis will help us to understand normal and abnormal development of the HPAG. In addition, these studies permit identification of candidate genes for human inborn errors of HPAG development.

Dax-1 (dosage-sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene 1) gene transcription is regulated by wnt4 in the female developing gonad

Dax-1 [dosage-sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene 1 (NR0B1)] is an orphan nuclear receptor acting as a suppressor of Ad4 binding protein/steroidogenic factor 1 [Ad4BP/SF-1 (NR5A1)] and as an anti-Sry factor in the process of gonadal sex differentiation. The roles of these nuclear receptors in the differentiation of the gonads and the adrenal cortex have been established through studies of the mutant phenotype in both mice and humans. However, the mechanisms underlying transcriptional regulation of these genes remain largely unknown. Here, we examined the relationship between Dax-1 gene transcription and the Wnt4 pathway. Reporter gene analysis revealed that Dax-1 gene transcription was activated by beta-catenin, a key signal-transducing protein in the Wnt pathway, acting in synergy with Ad4BP/SF-1. Interaction between beta-catenin and Ad4BP/SF-1 was observed using yeast two-hybrid and in vitro pull-down assays. The region of Ad4BP/SF-1 essential for this interaction consists of an acidic amino acid cluster, which resides in the first helix of the ligand-binding domain. Mutation of the amino acid cluster impaired transcriptional activation of Dax-1 as well as interaction of Ad4BP/SF-1 with beta-catenin. These results were supported by in vivo observations using Wnt4 gene-disrupted mice, in which Dax-1 gene expression was decreased significantly in sexually differentiating female gonads. We thus conclude that Wnt4 signaling mediates the increased expression of Dax-1 as the ovary becomes sexually differentiated.

Genetic network identification by high density, multiplexed reversed transcriptional (HD-MRT) analysis in steroidogenic axis model cell lines

Transcriptional network analysis in steroidogenic axis cell lines requires an understanding of cellular network composition and complexity. Previous studies have shown that absence of transcriptional network components in a cell line compromises that cell line's functional capacity for transcriptional regulation. Our goal was to analyze qualitatively steroidogenic axis-derived cell lines' expression of a putative transcriptional network involved in human and mouse development. To pursue this analysis we used Northern blots and a high density-multiplexed reverse transcription-polymerase chain reaction (HD-MRT-PCR) approach. Our results revealed that, while some members of this putative network were universally expressed, only a minority of the non-constitutive targeted transcripts were present in any single line. Based on our data and previously published results for contextual expression of these transcription factors, a model was constructed possessing the topology suggestive of a scale-free network: certain network members were highly connected nodes and would represent critical sites of vulnerability. The importance of these highly connected nodes for network function is supported by the severe phenotypes exhibited by human patients and animal models when these genes are mutated. We conclude that knowledge of network composition in specific cell lines is essential for their use as models to investigate functional interactions within selected subnetworks.

Sexually dimorphic expression of Dax-1 in the adrenal cortex

BACKGROUND

The DAX-1 (also known as AHC) gene encodes an unusual member of the nuclear receptor superfamily, and the gene product plays a pivotal role during gonadal and adrenal differentiation. Mutations of the human DAX-1 gene cause X-linked adrenal hypoplasia congenita associated with hypogonadotropic hypogonadism. However, the molecular mechanisms underlying the transcriptional regulation of the gene are not well understood.

RESULTS

Sexually dimorphic expression of Dax-1 (NR0B1) in the adrenal cortex was observed by RT-PCR, Western blotting and immunohistochemistry. The differential expression was abolished by gonadectomy and was restored again by sex steroid replacement. Our results suggested that the Dax-1 gene transcription is suppressed by androgens and androgen receptor (AR/NR3C4). Dax-1 gene transcription is regulated by Ad4BP/SF-1 (NR5A1), therefore we investigated the functional correlation between A4BP/SF-1 and AR. Interestingly, AR down-regulated the Dax-1 gene transcription mediated by Ad4BP/SF-1 in the presence of the ligand. DNA binding by AR was not essential for the suppressive action, however the suppression seemed to be dependent on the promoter contexts. An interaction between Ad4BP/SF-1 and AR was detected in the presence of the ligand for AR.

CONCLUSION

The present study revealed that the expression of Dax-1 in the adrenal cortex is regulated by androgen and the receptor. Interestingly, AR acts as a suppressor in the presence of the ligand through interaction with Ad4BP/SF-1.

The genetics of male undermasculinization

A review of the genetics of male undermasculinization must encompass a description of the embryology of the genital system. The dimorphism of sex development consequent upon the formation of a testis and the subsequent secretion of hormones to impose a male phenotype is highlighted. Thus, an understanding of the causes of male undermasculinization (manifest as XY sex reversal, complete and partial) includes reviewing the genetic factors which control testis determination and the production and action of testicular hormones. The study of disorders of male sex development has contributed substantially to knowledge of normal male development before birth. This knowledge has been complimented in recent years by the use of targeted murine gene disruption experiments to study the sex phenotype, although murine and human phenotypes are not always concordant. The investigation of disorders associated with male undermasculinization of prenatal onset is described briefly to complete the review.

Mutations in NR0B1 (DAX1) and NR5A1 (SF1) responsible for adrenal hypoplasia congenita

Adrenal hypoplasia congenita (AHC) causes primary adrenal insufficiency due to the failure of development of the adrenal cortex. Clinical and pedigree data indicate that the condition is genetically heterogeneous. The predominant adrenal hypoplasia congenita locus, however, is the NR0B1 gene, at Xp21, encoding the protein DAX1. In this article, we present a compendium of published NR0B1 mutations and polymorphisms, and discuss them in the contexts of known biology and clinical applicability. The recent descriptions of patients with primary adrenal insufficiency due to mutations of NR5A1, which encodes SF1, are also discussed.

Transcriptional regulators of steroidogenesis, DAX-1 and SF-1, are expressed in human skin

DAX-1 and SF-1 are members of the orphan nuclear receptor superfamily that are critical regulatory components of the hypothalamic-pituitary-adrenal-gonadal axis. In adrenal and gonadal tissues they regulate the expression of the cytochrome P450 steroid hydroxylase genes, key mediators of steroidogenesis. The identification of a number of steroid hydroxylases in human skin prompted us to investigate the presence of DAX-1 and SF-1. Immuno histochemical analysis of human skin revealed a distinctive staining pattern for DAX-1 and SF-1 in skin and its appendages. Prominent staining for DAX-1 was confined to the epidermis, sebaceous glands, sweat glands, and outer root sheath of the hair follicle with weaker expression in the inner root sheath, matrix cells, and dermal papilla cells. Similarly, SF-1 was also detected in the epidermis but displayed a scattered nuclear pattern across all layers. SF-1 immunoreactivity was also detected in the exocrine glands and was stronger than DAX-1 in the inner root sheath, matrix cells, and dermal papilla cells. Co-localization of DAX-1 and SF-1 was demonstrated by immunocytochemistry in the HaCaT keratinocyte cell line, primary keratinocytes, preadipocytes, and dermal papilla cells. Reverse transcriptase-polymerase chain reaction analysis demonstrated the expression of DAX-1 and SF-1 mRNA in whole human skin and Western analysis also confirmed the presence of DAX-1 protein in skin-derived cells. Our investigations demonstrate that two important regulators of steroidogeneisis are present in human skin and its appendages. These transcription factors may have a role in cutaneous steroidogenesis and thus be involved in hair follicle cycling or pathologies associated with steroids. Further studies are needed to determine the functional roles of DAX-1 and SF-1 in human skin.

Single-tube gene-specific expression analysis by high primer density multiplex reverse transcription

Molecular genetics is rapidly moving from simple identification of a gene of interest to characterization of gene products as components in complex networks. Critical tools for gene product analysis require a rapid method for evaluation of contextual expression. Here, we describe a robust, high primer density, single-tube, multiplex reverse transcription (HD-MRT) technique. This approach is capable of analyzing for the presence of numerous transcripts when polymerase chain reaction (PCR) is subsequently employed for individual gene-specific sequence amplification (HD-MRT-PCR). This assay substantially increases the total number of different cDNAs for amplification beyond previously published techniques. Our approach simultaneously eliminates RNA quality control issues for samples run in parallel while improving efficiency in the use of time and materials. This assay is designed for broad applicability and accessibility, employs modifications of commercially available components, and allows more than 25 independently selected gene-specific primers to be used simultaneously. Our protocol allows multiplexed primers to behave similarly to uniplex RT reactions, while avoiding potential interference between gene-specific and/or nonspecific primers during annealing and reverse transcription. Expression of putatively networked homologous transcripts was analyzed in multiple cell lines and tissues from mouse and human to validate the technique.

Genes essential for early events in gonadal development

The acquisition of a sexually dimorphic phenotype is a critical event in mammalian development. The basic underlying principle of sexual development is that genetic sex--determined at fertilization by the presence or absence of the Y chromosome--directs the embryonic gonads to differentiate into either testes or ovaries. Thereafter, hormones produced by the testes direct the developmental program that leads to male sexual differentiation. In the absence of testicular hormones, the female pathway of sexual differentiation occurs. Recent studies have defined key roles in gonadal development for two transcription factors: Wilms' tumor suppressor 1 (WT1) and steroidogenic factor 1 (SF-1). After presenting a brief overview of gonadal development and sexual differentiation, this chapter reviews the studies that led to the isolation and characterization of WT1 and SF-1, and then discusses how interactions between these two genes may mediate their key roles in a common developmental pathway.

Comparative localization of Dax-1 and Ad4BP/SF-1 during development of the hypothalamic-pituitary-gonadal axis suggests their closely related and distinct functions

Two nuclear receptors, Ad4BP/SF-1 and Dax-1, are essential regulators for development and function of the mammalian reproductive system. Similarity in expression sites, such as adrenal glands, gonads, pituitary, and hypothalamus, suggests a functional interaction, and the phenotype similarities were manifested in Ad4BP/SF-1-deficient mice and in cases of natural human mutations of Dax-1. In this study, quantitative reverse transcriptase polymerase chain reaction analyses revealed that expression profiles of Dax-1 in embryonic gonads are different between the two sexes and also from those of Ad4BP/SF-1. Immunohistochemical analyses clarified the spatial and temporal expressions of the Dax-1 protein during development of tissues composing the hypothalamic-pituitary-gonadal axis. During gonadal development, Dax-1 occurred after Ad4BP/SF-1 exhibiting a sexually dimorphic expression pattern at indifferent stages, indicating a possibility of Dax-1 involvement in earliest sex differentiation. When cord formation begins in the testis at embryonic day 12.5 (E12.5), Dax-1 was expressed strongly in Sertoli cells, but its expression level markedly decreased in Sertoli cells and increased in interstitial cells between E13.5 and E17.5. In the female, Dax-1 was strongly expressed in the entire ovarian primordium from E12.5 until E14.5, and then its expression level was decreased and limited to cells near the surface epithelium between E17.5 and postnatal day 0 (P0). During postnatal development of the testis, the variable staining of Dax-1 in Sertoli cells was detected as early as P7 and Dax-1-expressing Leydig cells became rare. In the postnatal ovary, Dax-1 expression was detected in granulosa cells with variable staining intensity, and occasionally in interstitial cells. During pituitary organogenesis, Dax-1 but not Ad4BP/SF-1 was expressed in the dorsal part of Rathke's pouch from E9.5. Later in development after E14.5, the distribution of Dax-1 overlapped with that of Ad4BP/SF-1, being restricted to gonadotropic cells in the anterior pituitary. In the ventromedial hypothalamus (VMH), Dax-1 and Ad4BP/SF-1 were mostly colocalized throughout the embryonic and postnatal development. Thus, the coexpression of Dax-1 and Ad4BP/SF-1 indicates their closely related functions in the development of the reproductive system. Furthermore, we noticed the presence of cells that express Dax-1 but not Ad4BP/SF-1, further indicating additional functions of Dax-1 in an Ad4BP/SF-1-independent molecular mechanism.

Sexual differentiation: from genes to gender

A person's sex can be considered across various levels. To illustrate, genes, hormones, and genitalia can all be considered physical markers of a person's sex. In addition to physical markers, behaviors such as gender role, gender identity and sexual orientation can be perceived as stereotypically male or female. The purpose of this review is to summarize current knowledge of sexual differentiation which emphasizes genetic and hormonal mechanisms that result in male and female development of gonads and genitalia. Finally, consideration is given to associations between genetic sex, gonadal sex, and hormonal sex with gender.

A novel mutation in DAX1 causes delayed-onset adrenal insufficiency and incomplete hypogonadotropic hypogonadism

Mutations in the DAX1 gene cause X-linked adrenal hypoplasia congenita (AHC) and hypogonadotropic hypogonadism (HHG). In affected boys, primary adrenal insufficiency occurs soon after birth or during early childhood; HHG is recognized at the expected time of puberty. In this report, we describe the novel phenotype of a man who presented with apparently isolated adrenal insufficiency at 28 years of age. Examination revealed partial pubertal development and undiagnosed incomplete HHG. Gonadotropin therapy did not improve his marked oligospermia, suggesting a concomitant primary testicular abnormality. Genomic analysis revealed a novel missense mutation, I439S, in DAX1. The mutant DAX-1 protein was studied for its ability to function as a transcriptional repressor of target genes. Consistent with the patient's mild clinical phenotype, the I439S mutation conferred intermediate levels of repressor activity of DAX-1 when compared with mutations associated with classic AHC. This unique case extends the clinical spectrum of AHC to include delayed-onset primary adrenal insufficiency in adulthood and milder forms of HHG. Furthermore, in accordance with findings in Ahch (Dax1) knockout mice, the clinical features in this patient suggest that DAX-1 function is required for spermatogenesis in humans, independent of its known effects on gonadotropin production.

An atypical kindred with X-linked adrenal hypoplasia congenita, normal puberty, and normal Dax-1 promoter and coding sequence

We report a Chinese kindred with an atypical sex-linked form of isolated adrenal hypoplasia without hypogonadotropic hypogonadism. Evidence of sex linkage was supported by DNA analysis using three polymorphic markers from the X-chromosome: a restriction fragment length polymorphism 200 kb centromeric of the DAX-1 gene, a tetranucleotide repeat marker in the DAX-1 promoter (DAX-P), and a microsatellite in the Duchenne muscular dystrophy locus (3'-19). This pedigree therefore presents the novel phenotype of sex-linked hypoadrenalism without hypogonadotropic hypogonadism, with evidence of possible linkage to the DAX-1 gene. However, all three affected individuals were examined for mutations in the DAX-1 gene, and found to have no sequence anomalies in the coding region, splice sites or 5' non-coding region. This presentation may be due to a defect in the DAX-1 gene outside its known coding region, possibly modulated by functional polymorphisms at other loci, and/or environmental effects, or to a defect in a novel gene on the X chromosome which selectively influences adrenal development.

Dax-1 as one of the target genes of Ad4BP/SF-1

The DAX-1 (also known as AHC) gene encodes an unusual member of the nuclear hormone receptor superfamily. DAX-1 plays a critical role during gonadal and adrenal differentiation since mutations of the human DAX-1 gene cause X-linked adrenal hypoplasia congenita associated with hypogonadotropic hypogonadism. In recent studies, DAX-1 was reported to function as a transcriptional suppressor of Ad4BP/SF-1, a critical transcription factor in gonadal and adrenal differentiation. With respect to implication of Ad4BP/SF-1 in the transcriptional regulation of the DAX-1 gene, inconsistent findings have been previously reported. We investigated the upstream region of the mouse Dax-1 (also known as Ahch) gene and identified a novel Ad4/SF-1 site by transient transfection and electrophoretic mobility shift assays. In addition, immunohistochemical analyses with a specific antibody to Dax-1 indicated the presence of immunoreactive cells in steroidogenic tissues, pituitary gland, and hypothalamus. Although the distributions of Dax-1 and Ad4BP/SF-1 were very similar, they were not completely identical. The expression of Dax-1 was significantly impaired in knock-out mice of the Ftz-f1 gene, which encodes Ad4BP/ SF-1. Taken together, our findings indicate that Ad4BP/SF-1 controls the transcription of the Dax-1 gene.

Steroidogenic factor-1: its role in endocrine organ development and differentiation

The cloning of the first steroid hormone receptor over a decade ago provided vital insight into the mechanisms by which steroid hormones activate gene transcription. When bound by hormone, these receptors function as ligand-dependent transcription factors by binding to unique response elements in the promoter of specific target genes. Over 60 receptors have now been characterized in this superfamily of steroid receptors. Many receptors known as orphan receptors have been cloned by homology and have no known ligands but appear to be mediators of endocrine function in the adult and in many cases are essential developmental regulators in endocrine organogenesis. One such receptor is steroidogenic factor-1 (SF-1). While initially cloned as a transcriptional regulator of the various steroidogenic enzyme genes in the adrenal and gonad, it has become clear through genetic ablation experiments in mice that SF-1 is an essential factor in adrenal and gonadal development and for the proper functioning of the hypothalamic-pituitary-gonadal axis. In addition, these studies have revealed that SF-1 is necessary for the formation of the ventromedial nucleus of the hypothalamus. While we have learned much since the initial cloning of SF-1, the mechanisms by which SF-1 regulates these various developmental programs remain elusive. This article focuses on the characterization of SF-1 and its emerging role in endocrine homeostasis. Specific attention is placed on the mechanisms of action of this unique member of the nuclear receptor superfamily.

Gene interactions in gonadal development

The acquisition of a sexually dimorphic phenotype is a critical event in mammalian development. Although the maturation of sexual function and reproduction occurs after birth, essentially all of the critical developmental steps take place during embryogenesis. Temporally, these steps can be divided into two different phases: sex determination, the initial event that determines whether the gonads will develop as testes or ovaries; and sexual differentiation, the subsequent events that ultimately produce either the male or the female sexual phenotype. A basic tenet of sexual development in mammals is that genetic sex--determined by the presence or absence of the Y chromosome--directs the embryonic gonads to differentiate into either testes or ovaries. Thereafter, hormones produced by the testes direct the developmental program leading to male sexual differentiation. In the absence of testicular hormones, the pathway of sexual differentiation is female. This chapter reviews the anatomic and cellular changes that constitute sexual differentiation and discusses SRY and other genes, including SF-1, WT1, DAX-1, and SOX9, that play key developmental roles in this process. Dose-dependent interactions among these genes are critical for sex determination and differentiation.

The Wilms' tumor suppressor gene (wt1) product regulates Dax-1 gene expression during gonadal differentiation

Gonadal differentiation is dependent upon a molecular cascade responsible for ovarian or testicular development from the bipotential gonadal ridge. Genetic analysis has implicated a number of gene products essential for this process, which include Sry, WT1, SF-1, and DAX-1. We have sought to better define the role of WT1 in this process by identifying downstream targets of WT1 during normal gonadal development. We have noticed that in the developing murine gonadal ridge, wt1 expression precedes expression of Dax-1, a nuclear receptor gene. We document here that the spatial distribution profiles of both proteins in the developing gonad overlap. We also demonstrate that WT1 can activate the Dax-1 promoter. Footprinting analysis, transient transfections, promoter mutagenesis, and mobility shift assays suggest that WT1 regulates Dax-1 via GC-rich binding sites found upstream of the Dax-1 TATA box. We show that two WT1-interacting proteins, the product of a Denys-Drash syndrome allele of wt1 and prostate apoptosis response-4 protein, inhibit WT1-mediated transactivation of Dax-1. In addition, we demonstrate that WT1 can activate the endogenous Dax-1 promoter. Our results indicate that the WT1-DAX-1 pathway is an early event in the process of mammalian sex determination.

Three steroidogenic factor-1 binding elements are required for constitutive and cAMP-regulated expression of the human adrenocorticotropin receptor gene

In the present study, we characterized two new SF-1 binding sites, SF-209 and SF-98, in the promoter of the human ACTH receptor (hACTH-R) gene. Both sites, together with the previously described SF-35 site, are required for full constitutive activity of this gene. This was demonstrated by the use of constructs containing part of the promoter upstream of the luciferase gene and carrying mutation in one of these sites, to transiently transfect H295R cells. Mutations of either SF-35, SF-98, or SF-209 induced a decrease of luciferase activity. This effect was amplified when two or three elements were mutated together in the same construct. Only SF-35 and SF-98 seem to play a major role in the cAMP-induced regulation of the hACTH-R gene, since mutation of either one of these sites reduced the forskolin induction of luciferase activity by 50%. When both elements were mutated, no stimulation was obtained over the control. This indicates that SF-1 protein must bind to both sites for the cAMP response.

Expression of chicken steroidogenic factor-1 during gonadal sex differentiation

The orphan nuclear receptor, steroidogenic factor-1 (SF-1), regulates steroidogenic enzyme expression and is essential for gonadal and adrenal development in mammals. We have examined expression of the chicken homologue, cSF-1, during gonadal sex differentiation using whole mount in situ hybridisation and RNase protection assays (RPA). In the youngest embryos examined (day 3.5; stages 21-22), cSF-1 transcripts were already detectable by in situ hybridisation in the undifferentiated genital ridge of both sexes. Expression continued in the gonads of both sexes at the time of sexual differentiation (days 5.5-6.5; stages 28-30). Expression then became higher in developing ovaries compared to testes at days 6.5-8. 5 (stages 30-35). At day 13.5 (stage 40), when the gonads are well differentiated, both ovaries and testes showed cSF-1 expression, with higher levels of expression in the left ovary compared to the right (regressing) gonad in females and compared to testes. RPA analysis of isolated gonads confirmed higher expression of SF-1 in differentiating ovaries relative to testes. Expression of cSF-1 in the developing adrenal gland was similar for both sexes at all stages examined. In tissue sections of day 8.5 whole mount gonads, cSF-1 expression was localised in the medulla of the ovary and was weakly detectable in the testis. These observations indicate that SF-1 has a conserved role in early gonadal and adrenal development in vertebrates. However, upregulation of cSF-1 expression during ovarian differentiation is opposite to the pattern seen in mammals, in which SF-1 is downregulated in females. This difference between the birds and mammals may reflect differences in steroidogenic activity of the embryonic ovary versus the testis in the two groups.

Porcine steroidogenic factor-1 gene (pSF-1) expression and analysis of embryonic pig gonads during sexual differentiation

The porcine steroidogenic factor-1 gene (pSF-1) was cloned using a combination of genomic and RT-PCR based cloning methods. pSF-1 consists of an open reading frame of 1383 nt corresponding to a deduced amino acid sequence of 461 aa, similar to bovine and human SF-1. Sequence homologies between pSF-1 and human, bovine and mouse molecules indicate strong evolutionary conservation at both the nt and aa levels. Northern analysis of pSF-1 expression in adult steroidogenic tissues correlated with porcine steroidogenic acute regulatory protein gene (pStAR) and porcine side chain cleavage (pP450scc) gene expression. Notably, pSF-1 expression was readily detected in neonatal testes, absent at 3 weeks of age, and again readily detected at 3 months and in adult testes. pSF-1 expression was weak but detectable in placental tissues at various times of gestation, and was correlated with pStAR and pP450scc expression, indicating classical steroidogenesis in this organ. In developing gonads from 6-12 weeks of gestation, i.e. during the time of sex differentiation in the pig, Northern analysis demonstrated increasing expression of PSF-1 in fetal testes and no expression in ovaries. This expression pattern was paralleled for pStAR, pP450scc, and porcine Müllerian inhibitory substance (pMIS), consistent with pSF-1 involvement in both steroid and protein hormone secretions of the developing testes during sex differentiation. Porcine SRY HMG-box related gene-9 (pSOX-9) expression also paralleled that of pSF-1 in developing testes. In contrast, DSS-AHC critical region on the X chromosome, gene 1 (pDAX-1) was expressed predominantly in the developing ovaries, indicating a possible reciprocal regulation of pSF-1 and pDAX-1 genes in developing pig testes and ovaries.

Congenital adrenal hypoplasia: clinical spectrum, experience with hormonal diagnosis, and report on new point mutations of the DAX-1 gene

X-linked congenital adrenal hypoplasia (AHC) is a rare developmental disorder of the human adrenal cortex and is caused by deletion or mutation of the DAX-1 gene, a recently discovered member of the nuclear hormone receptor superfamily. Hypogonadotropic hypogonadism is frequently associated with AHC. AHC occurs as part of a contiguous gene syndrome together with glycerol kinase deficiency (GKD) and Duchenne's muscular dystrophy. The present series, collected over the past 2 decades, includes 18 AHC boys from 16 families: 4 with AHC, GKD, and Duchenne's muscular dystrophy; 2 with AHC and GKD; and 12 with AHC (5 young adults with hypogonadotropic hypogonadism). Most of the boys presented with salt wasting and hyperpigmentation during the neonatal period. Plasma steroid determinations performed in the first weeks of life often showed confusing results, probably caused by steroids produced in the neonates' persisting fetocortex. Aldosterone deficiency usually preceded cortisol deficiency, which explains why the patients more often presented with salt-wasting rather than with hypoglycemic symptoms. An ACTH test was often necessary to detect cortisol deficiency in the very young infants. In some patients, serial testing was necessary to establish the correct diagnosis. In 4 boys studied during the first 3 months after birth, we found pubertal LH, FSH, and testosterone plasma levels indicating postnatal transient activation of the hypothalamic-pituitary-gonadal axis as in normal boys. Previous studies have shown that the DAX-1 gene is deleted in the AHC patients with a contiguous gene syndrome and is mutated in nondeletion patients. Most of the point mutations identified in AHC patients were frameshift mutations and stop mutations. In the 15 patients available for molecular analysis of the DAX-1 gene, there were large deletions in 6 patients and point mutations in another 7 patients. All of the point mutations identified in the present study resulted in a nonfunctional truncated DAX-1 protein. Two brothers with primary adrenal insufficiency and a medical history that strongly suggested AHC had no mutation in the DAX-1 gene. Thus, additional, as yet unknown genes must play a part in normal adrenal cortical development.

A steroidogenic factor-1 binding element is essential for basal human ACTH receptor gene transcription

We have previously shown that the promoter of the human ACTH receptor (ACTH-R) contains, at -35 bp, a binding site for the steroidogenic factor 1 (SF-1), an orphan nuclear receptor which could be responsible for the transcriptional activity of this promoter. In the present study, electrophoretic mobility shift assays demonstrated that the sequence -43/-19 bound the SF-1 protein present in the nuclear extracts of adrenocortical cells. Mutation of the SF-1 binding site markedly reduced (40%) the basal transcription of the reporter gene in Y-1 cells transfected with the mutated p(-56/+22)GH construct compared to the wild-type construct. These results demonstrate that the SF-1 binding element present in this fragment is required for the basal promoter activity of the human ACTH-R gene. In addition, other binding elements located upstream from this characterized SF-1 binding site are involved in the full basal promoter activity of the human ACTH-R since transfection studies with a longer p(-1017/+22)GH construct resulted in a higher GH release than with the p(-56/+22)GH construct.

Expression of an orphan nuclear receptor DAX-1 in human pituitary adenomas

OBJECTIVES

An orphan nuclear receptor, DAX-1, is known to be involved in the development and differentiation of anterior pituitary cells. The present study aimed to examine 1) whether DAX-1 is expressed in human pituitary adenomas, and 2) if it is expressed, what types of adenoma express the factor.

MATERIALS AND METHODS

Adenoma tissues examined included 18 clinically non-functioning adenomas, 14 GH-secreting adenomas and 7 PRL-secreting adenomas. The expression of the following genes were tested by reverse transcription-polymerase chain reaction (RT-PCR): DAX-1, Adrenal-4-binding protein/steroidogenic factor-1 (Ad4BP/SF-1), Pit-1, LH beta, FSH beta, gonadotrophin-releasing hormone receptor (GnRH-R), GH, PRL, and TSH beta, as well as beta-actin as a control.

RESULTS

Eleven clinically non-functioning adenomas expressed DAX-1, 10 of which also expressed Ad4BP/SF-1. Nine out of the 11 DAX-1 expressing adenomas also expressed LH beta, FSH beta and GnRH-R as well, indicating that these adenomas possessed gonadotrophic properties. Nine clinically non-functioning adenomas expressed Pit-1 as well as GH, PRL and/or TSH beta, thus having somatomammotrophic or thyrotrophic properties, 3 of which overlapped with the above DAX-1-expressing adenomas. One non-functioning adenoma expressed Ad4BP/SF1 and FSH beta but not DAX-1, and another one expressed DAX-1 and Ad4BP/SF-1 with PRL. On the other hand, all GH-secreting and PRL-secreting adenomas expressed Pit-1 and GH and/or PRL, but neither DAX-1 nor Ad4BP/SF-1.

CONCLUSIONS

The results shown here indicate that DAX-1 is expressed in the majority of human pituitary adenomas of gonadotrophic origin in parallel with Adrenal-4-binding protein/steroidogenic factor-1.