Identical origin of adrenal cortex and gonad revealed by expression profiles of Ad4BP/SF-1

The foetal Leydig cell-- differentiation, function and regulation

The foetal Leydig cell population arises shortly after testicular differentiation at around 12.5 dpc in the mouse and 6 weeks in the human. These cells function, primarily, to produce androgens which are essential for masculinization of the foetus. The origin of the foetal Leydig cells remains uncertain but it has been suggested that adrenocortical cells and foetal Leydig cells may share a common origin in an adreno-genital primordium. Studies in the mouse are beginning to identify factors such as desert hedgehog and platelet-derived growth factor which are required for foetal Leydig cell development. Regulation of foetal Leydig cell function remains uncertain in most species. Unlike the adult population of Leydig cells, the foetal Leydig cells in the mouse do not require luteinizing hormone (LH) to stimulate androgen production. An intact pituitary does appear to be required, however, and adrenocorticotrophic hormone (ACTH) will stimulate foetal Leydig cell function directly suggesting that both LH and ACTH act to maintain Leydig cell function in vivo. In the human LH/hCG is required for foetal Leydig cell function although the cells may also be sensitive to ACTH.

Identification and lineage tracing of two populations of somatic gonadal precursors in medaka embryos

The gonad contains two major cell lineages, germline and somatic cells. Little is known, however, about the somatic gonadal cell lineage in vertebrates. Using fate mapping studies and ablation experiments in medaka fish (Oryzias latipes), we determined that somatic gonadal precursors arise from the most posterior part of the sdf-1a expression domain in the lateral plate mesoderm at the early segmentation stage; this region has the properties of a gonadal field. Somatic gonadal precursors in this field, which continuously express sdf-1a, move anteriorly and medially to the prospective gonadal area by convergent movement. By the stage at which these somatic gonadal precursors have become located adjacent to the embryonic body, the precursors no longer replace the surrounding lateral plate mesoderm, becoming spatially organized into two distinct populations. We further show that, prior to reaching the prospective gonadal area, these populations can be distinguished by expression of either ftz-f1 or sox9b. These results clearly indicate that different populations of gonadal precursors are present before the formation of a single gonadal primordium, shedding new light on the developmental processes of somatic gonadal cell and subsequent sex differentiation.

Differential gene dosage effects of Ad4BP/SF-1 on target tissue development

Ad4BP/SF-1 (NR5A1) was identified as a key regulator of the hypothalamus-pituitary-gonadal and -adrenal axes. Loss-of-function studies revealed that Ad4BP/SF-1 is essential for the development of these tissues and spleen. Here, we generated transgenic mouse with BAC recombinants carrying a dual promoter and Tet-off system. These recombinants have a potential to express lacZ and Ad4BP/SF-1 in the tissues where endogenous Ad4BP/SF-1 is expressed. However, protein level of Ad4BP/SF-1 varied among the tissues of the transgenic mice and probably thereby the target tissues are affected differentially. The BAC-transgenic mice were applied to rescue Ad4BP/SF-1 KO mouse. Interestingly, the mice successfully rescued the gonad and spleen but failed to rescue the adrenal gland. This variation might be dependent on in part the protein expression levels among the tissues and in part on differential sensitivities to the gene dosage.

Le développement de la surrénale humaine

The human adrenal is an endocrine gland located at the superior part of the kidney. Composed of the adrenal cortex of mesoblastic origin and the adrenal medulla of neuroectoblastic origin, the human fetal adrenal grows considerably during the first three months of development. From 12 to 18 weeks of development (WD), the weight of the adrenals increases seven-fold. The gland's weight doubles from 18 to 28 WD and from 28 to 36 WD. At birth, the two adrenals weigh on average 10 g. At the 8th week, two zones are individualized in the adrenal cortex: the definitive zone and the fetal inner zone. At the second trimester, according to ultrastructural and biochemical studies, a third zone, called the transition zone, is individualized between the definitive zone and the fetal inner zone. The definitive zone persists, but the origin of the three zones (glomerular, fascicular and reticular) of adult adrenal cortex is not known. The fetal inner zone regresses from the 5th month of gestation and disappears totally one year after birth. At the 8th week, the immature neuroblasts migrate to the definitive zone, then to the fetal inner zone to compose the adrenal medulla, which develops essentially after birth and during the first year. Before the 10th week, the human fetal adrenal is able to produce steroid hormones, in particular dehydroepiandrosterone sulfate (DHEA-S); the secretion of cortisol remains discussed. The development of the human fetal adrenal is complex and is under the control of hormones (ACTH, LH and betaHCG), growth factors (ACTH essentially) and transcription factors (essentially SF1 and DAX-1). Knowledge of morphological and molecular phenomena of this development permits to understand the pathophisiology of congenital adrenal deficiencies.

SF-1/Ad4BP transforms primary long-term cultured bone marrow cells into ACTH-responsive steroidogenic cells

Bone marrow stem cells develop into haematopoietic and mesenchymal lineages, but have not been known to participate in steroidogenic cell production. Steroidogenic factor 1 (SF-1), also designated adrenal 4 binding protein (Ad4BP), is an essential orphan nuclear receptor for steroidogenesis as well as for adrenal and gonadal gland development. In the present study, we revealed that the adenovirus-mediated forced expression of SF-1 can transform cultured primary long-term cultured bone marrow cells into steroidogenic cells, showing the de novo synthesis of multiple steroid hormones in response to adrenocorticotropic hormone (ACTH). This finding may provide an initial step in innovative autograft cell transfer therapy for steroid hormone deficiencies.

A FTZ-F1-containing yeast artificial chromosome recapitulates expression of steroidogenic factor 1 in vivo

Steroidogenic factor 1 (SF-1/Nr5a1) is an orphan nuclear receptor encoded by the Ftz-F1 gene and is required for gonad and adrenal development and regulation of hormone production within the reproductive and adrenal axes. To extend our understanding of Ftz-F1 and its role in SF-1 expression, we identified and characterized a yeast artificial chromosome (YAC) containing Ftz-F1. Within this YAC, Ftz-F1 is centrally located and flanked by genes encoding a second orphan nuclear receptor, germ cell nuclear factor, and proteasome (prosome, macropain) subunit beta type 7. Three lines of transgenic mice carrying the YAC were generated and in two lines (lines 7 and 14), RT-PCR and ribonuclease protection analysis showed that expression of transgenic SF-1 mimicked that of endogenous SF-1, both spatially and quantitatively. In the third line (line 15), pituitary and hypothalamic expression were absent. Comparison of the integrated transgenes revealed that line 15 was truncated at the end of intron 4 and revealed a region within the locus that is responsible for SF-1 expression in the pituitary and hypothalamus. The line 14 transgene was introduced into a mouse strain lacking functional SF-1. Examination of SF-1-deficient, transgene-positive mice revealed that the YAC was able to rescue adrenal and gonad development, which normally arrests in the SF-1-null embryos and showed that the 153-kb transgene integrated in line 14 is sufficient to properly direct SF-1 expression and support its biological activity. Thus, the study defines a region of Ftz-F1 that contains the requisite set of regulatory elements to direct SF-1 cell-specific expression and all temporal and quantitative changes need for its biological activity.

Influence on spatiotemporal patterns of a male-specific Sox9 activation by ectopic Sry expression during early phases of testis differentiation in mice

Testis induction is associated with gonadal Sry and Sox9 expression in mammals. This study investigated whether Sry expression directly induces male-specific Sox9 activation during early phases of testis differentiation. We have established an XX sex-reversal mouse line carrying the Sry transgene driven by a weak basal promoter of the Hsp70.3 gene (Hsp-Sry), whereby the transgene was activated in the gonads along the entire anteroposterior axis from earlier stages. The effects of misexpression and overexpression of Sry on the spatiotemporal pattern of Sox9 expression were examined using both XX and XY gonads of Hsp-Sry transgenic embryos. It was shown that ectopic expression of Sry transcripts in the entire gonadal area from earlier stages promotes neither any advance in the timing nor any appreciable ectopic activation of endogenous Sox9 expression. Immediately after the onset of Sox9 activation, however, both the level of Sox9 expression and the number of SOX9-positive cells were significantly enhanced in Hsp-Sry/XY gonads, as compared with those in wild-type/XY and Hsp-Sry/XX gonads. These findings suggest that, although Sry is capable of up-regulating Sox9 expression dose-dependently, Sry mRNA expression alone is not likely to provide positional or timing information needed for male-specific Sox9 activation in developing XY gonads.

Mesonephric FGF signaling is associated with the development of sexually indifferent gonadal primordium in chick embryos

The gonad as well as the reproductive tracts, kidney, and adrenal cortex are derived from the intermediate mesoderm. In addition, the intermediate mesoderm forms the mesonephros. Although the mesonephros is the source of certain testicular cell types, its contribution to gonad formation through expression of growth factors is largely unknown. Here, we examined the expression profiles of FGF9 in the developing mesonephros of chick embryos at sexually indifferent stages, and found that the expression domain is adjacent to the gonadal primordium. Moreover, FGFR3 (FGF receptor 3) showed a strong expression in the gonadal primordium. Next, we examined the functions of FGF signal during gonadal development with misexpressed FGF9. Interestingly, misexpression of FGF9 led to gonadal expansion through stimulation of cell proliferation. In contrast, treatment with a chemical inhibitor for FGFR decreased cell proliferation and resulted in reduction of the gonadal size. Simultaneously, the treatment resulted in reduction of gonadal marker gene expression. Our study demonstrated that FGF expressed in the developing mesonephros is involved in the development of the gonad at the sexually indifferent stages through stimulation of gonadal cell proliferation and gonadal marker gene expression.

Pbx1 is essential for adrenal development and urogenital differentiation

Pbx1 encodes a TALE (three amino acid loop extension) class homeodomain protein that participates in multimeric transcriptional complexes to regulate developmental gene expression. Previous studies demonstrate a critical role for Pbx1 as a developmental regulator whose absence results in embryonic lethality and multiple tissue and organ system abnormalities. Here we report a requirement for Pbx1 in the differentiation of urogenital organs, where Pbx1 is widely expressed in mesenchymal tissues. The complete lack of adrenal glands and formation of gonads displaying rudimentary sexual differentiation correlated with decreased cellular proliferation in Pbx1(-/-) genital ridges. Furthermore, expression of steroidogenic factor-1 (SF-1), a nuclear receptor essential for adrenal organogenesis, was reduced to minimal levels in Pbx1 mutants, indicating an upstream function for Pbx1 in adrenocortical development. Finally, loss of Pbx1 markedly reduces urogenital ridge outgrowth and results in impaired differentiation of the mesonephros and kidneys and the absence of Müllerian ducts. These findings establish a Pbx1-dependent pathway that regulates the expansion of SF-1 positive cells essential for adrenal formation and gonadal differentiation and demonstrate an early requirement for Pbx1 in urogenital development.

Renin cells are precursors for multiple cell types that switch to the renin phenotype when homeostasis is threatened

Renin-synthesizing cells are crucial in the regulation of blood pressure and fluid-electrolyte homeostasis. Adult mammals subjected to manipulations that threaten homeostasis increase circulating renin by increasing the number of renin-expressing/-releasing cells. We hypothesize that the ability of adult cells to synthesize renin does not occur randomly in any cell type, depending instead on the cell's lineage. To determine the fate of renin-expressing cells, we generated knockin mice expressing cre recombinase in renin-expressing cells and crossed them with reporter mice. Results show that renin-expressing cells are precursors for a variety of cells that differentiate into non-renin-expressing cells such as smooth-muscle, epithelial, mesangial, and extrarenal cells. In the kidney, these cells retain the capability to synthesize renin when additional hormone is required to reestablish homeostasis: specific subpopulations of apparently differentiated cells are "held in reserve" to respond (repeatedly) by de-differentiating and expressing renin in response to stress, and re-differentiating when the crisis passes.

Dependence of fetal hairs and sebaceous glands on fetal adrenal cortex and possible control from adrenal medulla

Human fetal adrenal development is characterized by rapid growth, high steroidogenic activity, and a distinct morphology, including a unique cortical compartment known as the fetal zone. For most of gestation, the predominant fetal zone accounts for 80-90% of the cortical volume and is the primary site of growth and steroidogenesis, producing 100-200 mg/day of the androgenic steroid, dehydroepiandrosterone sulfate (DHEA-S). The physiological role of this zone during intrauterine life is not well understood. While the glands appear to be capable of DHEA-S synthesis early in gestation (8-10 weeks), we noticed that this event precedes the differentiation of hairs and sebaceous glands. Hairs begin to develop between 9 and 12 weeks and sebaceous glands between 13 and 15 weeks of gestation. Sebaceous glands form an oily secretion - sebum that mixes with desquamated epidermal cells to form vernix caseosa. Vernix caseosa protects the developing skin from constant exposure to amniotic fluid, and hairs helps to hold the vernix caseosa on the skin. We suggest therefore that the human fetal adrenal cortex produces DHEA-S beginning at around 8-10 weeks of gestation in sufficient quantities to influence the growth of hairs and sebaceous glands. Soon after birth, the fetal zone atrophies, and adrenal androgen production decreases to minimal levels. As a consequence, in concordance with the rapid decrease in adrenal androgen levels and in consistent with our hypothesis, fetal hairs are shed and sebaceous glands shrink to small structures. The mechanism that regulates fetal adrenal androgen production is a key unanswered problem in human adrenal biology. Since there exists a close relationship between epinephrine and DHEA-S levels during adrenarche which shows modulatory interactions between adrenal androgen production and adrenomedullary function, we suggest again that adrenomedullary function might play a role in the control of fetal adrenal androgen secretion.

Regionally distinct potencies of mouse XY genital ridge to initiate testis differentiation dependent on anteroposterior axis

In mouse gonadal differentiation, the center-to-pole Sry expression pattern suggests the regionally distinct potencies of the genital ridge, which induce testis differentiation. In this study, we examined the anteroposterior axis-dependent differences in testis-differentiation potencies by using cultures of anterior, middle, and posterior segments of the XY genital ridge. The inducible pattern of Sertoli cell differentiation showed a center-to-pole wave similar to the initial Sry expression pattern. In contrast, the ability to induce Leydig cell differentiation emanated from the anterior segment and then spread to the posterior side. These findings suggest the presence of two distinct dynamic waves in the capacity of the genital ridge to induce Sertoli or Leydig cell differentiation at early phases of testis differentiation.

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.

Mouse strain susceptibility to gonadectomy-induced adrenocortical tumor formation correlates with the expression of GATA-4 and luteinizing hormone receptor

Certain inbred strains of mice, including DBA/2J, develop adrenocortical tumors in response to gonadectomy. Spindle-shaped cells with limited steroidogenic capacity, termed A cells, appear in the subcapsular region of the adrenal gland, followed by sex steroid-producing cells known as B cells. These changes result from unopposed gonadotropin production by the pituitary, but the adrenocortical factors involved in tumorigenesis have not been characterized. GATA-4, a transcription factor normally expressed in fetal, but not adult, adrenocortical cells, was found in neoplastic cells that proliferate in the adrenal cortex of gonadectomized DBA/2J mice. GATA-4 mRNA was detected in the adrenal glands of female mice 0.5 months after ovariectomy and reached a maximum by 4 months. Castrated male mice developed adrenocortical tumors more slowly than gonadectomized females, and the onset of GATA-4 expression in the adrenal was delayed. In situ hybridization and immunohistochemistry revealed GATA-4 mRNA and protein in A and B cells, but not in normal adrenocortical cells. mRNA encoding another factor associated with adrenocortical tumorigenesis, LH receptor (LHR), was detected in A and B cells. In addition, transcripts for P450 17 alpha-hydroxylase/C17-C20 lyase, an enzyme essential for the production of sex steroids, and inhibin-alpha were found in B cells. Unilateral ovarian regeneration, a phenomenon known to occur in gonadectomized mice, was observed in a subset of DBA/2J mice undergoing complete ovariectomy. In these animals, adrenocortical tumor progression was arrested; A cells and GATA-4 expression were evident, but there was no expression of LHR or P450 17 alpha-hydroxylase/C17-C20 lyase. Strain susceptibility to adrenocortical tumorigenesis (DBA/2J >> FVB/N) correlated with the expression of GATA-4 and LHR, implicating these factors in the process of adrenocortical neoplasia in response to continuous gonadotropin stimulation.

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.

Adrenocorticotropic hormone directly stimulates testosterone production by the fetal and neonatal mouse testis

Adult Leydig cell steroidogenesis is dependent on LH but fetal Leydig cells can function independently of gonadotropin stimulation. To identify factors that may be involved in regulation of fetal Leydig cells expressed sequence tag libraries from fetal and adult testes were compared, and fetal-specific genes identified. The ACTH receptor [melanocortin type 2 receptor (Mc2r)] was identified within this fetal-specific group. Subsequent real-time PCR studies confirmed that Mc2r was expressed in the fetal testis at 100-fold higher levels than in the adult testis. Incubation of fetal or neonatal testes with ACTH in vitro stimulated testosterone production more than 10-fold, although ACTH had no effect on testes from animals aged 20 d or older. The steroidogenic response of fetal and neonatal testes to a maximally stimulating dose of human chorionic gonadotropin was similar to the response shown to ACTH. The ED(50) for ACTH, measured in isolated fetal and neonatal testicular cells, was 5 x 10(-10) M and the lowest dose of ACTH eliciting a response was 2 x 10(-11) M. Circulating ACTH levels in fetal mice were around 8 x 10(-11) M. Neither alpha-MSH nor gamma-MSH had any effect on androgen production in vitro at any age. Fetal testosterone levels were normal in mice that lack circulating ACTH (proopiomelanocortin-null) indicating that ACTH is not essential for fetal Leydig cell function. Results show that both LH and ACTH can regulate testicular steroidogenesis during fetal development in the mouse and suggest that fetal Leydig cells, but not adult Leydig cells, are sensitive to ACTH stimulation.

The complex life of WT1

The Wilms' tumour gene, WT1, encodes a zinc-finger transcription factor that is inactivated in a subset of Wilms' tumours. Mutation analysis in human patients and genetic experiments in mice have revealed that WT1 has a role much wider than just tumour suppression. Alternative splicing, RNA editing, and the use of alternative translation initiation sites generate a multitude of isoforms, which seem to have overlapping but also distinct functions during embryonic development and the maintenance of organ function. Recently, mouse strains lacking the WT1(-KTS) or WT1(+KTS) splice variants of exon 9 were generated. More severe defects of kidneys and gonads are found in mice lacking the WT1(-KTS) variant. Animals lacking the WT1(+KTS) variant show disturbed podocyte function and male-to-female sex reversal. Alternative splicing of exon 5, however, might not modify WT1 function dramatically. Recently, it was also described that reduction of WT1 levels in the kidney results in glomerulosclerosis and upregulation of WT1 in the heart might contribute to neovascularization after infarction.

Pdgfr-alpha mediates testis cord organization and fetal Leydig cell development in the XY gonad

During testis development, the rapid morphological changes initiated by Sry require the coordinate integration of many signaling pathways. Based on the established role of the platelet-derived growth factor (PDGF) family of ligands and receptors in migration, proliferation, and differentiation of cells in various organ systems, we have investigated the role of PDGF in testis organogenesis. Analysis of expression patterns and characterization of the gonad phenotype in Pdgfr-alpha(-/-) embryos identified PDGFR-alpha as a critical mediator of signaling in the early testis at multiple steps of testis development. Pdgfr-alpha(-/-) XY gonads displayed disruptions in the organization of the vasculature and in the partitioning of interstitial and testis cord compartments. Closer examination revealed severe reductions in characteristic XY proliferation, mesonephric cell migration, and fetal Leydig cell differentiation. This work identifies PDGF signaling through the alpha receptor as an important event downstream of Sry in testis organogenesis and Leydig cell differentiation.

Development of a transgenic green fluorescent protein lineage marker for steroidogenic factor 1

Knockout (KO) mice lacking steroidogenic factor 1 (SF-1, officially designated Nr5a1) have a complex phenotype that includes adrenal and gonadal agenesis, impaired function of pituitary gonadotropes, and abnormalities of the ventromedial hypothalamic nucleus (VMH). To develop a lineage marker for cells that express SF-1, we used bacterial artificial chromosome (BAC) transgenesis. A BAC fragment containing 50 kb of the mouse Nr5a1 gene was placed upstream of the coding sequence for enhanced green fluorescent protein (eGFP) and used to generate SF-1/eGFP transgenic mice. These sequences directed eGFP expression to multiple cell lineages that express SF-1, including steroidogenic cells of the adrenal cortex, testes, and ovaries, VMH neurons, and reticuloendothelial cells of the spleen. Despite the essential role of SF-1 in gonadotropes, eGFP was not expressed in the anterior pituitary. These studies show that 50 kb of the mouse Nr5a1 gene can target transgenic expression to multiple cell lineages that normally express SF-1. The SF-1/eGFP transgene provides a valuable tool to expand our understanding of the actions of SF-1 in endocrine development and function.

Leydig cells of the human testis possess astrocyte and oligodendrocyte marker molecules

It has been established, that Leydig cells of the human testis possess neuroendocrine properties and are therefore a member of the diffuse neuroendocrine (paraneuron) system. In the present study, we examined whether Leydig cells of adult (51-86 year of age) and developing (between the 15th and 36th week of gestation) human testes are immunopositive for glial cell-specific antigens such as glial fibrillary acidic protein (GFAP), galactocerebroside (GalC), cyclic 2',3'-nucleotide-3'-phosphodiesterase (CNPase), A2B5-antigen (A2B5) and O4-antigen (O4). With the use of Western blots and dot blot analyses, respectively, GFAP, CNPase, GalC, A2B5 and O4 were found in whole testes and Leydig cell protein extracts of adult men. Corresponding immunohistochemical studies revealed presence of these antigens in the cytoplasm of Leydig cells both of adult testes and testes during prenatal development. Some differences in staining intensity of single antigens were observed probably depending on the functional and/or developmental stage of the single cells. In addition, GFAP-, GalC- and CNPase-immunopositivity was found in numerous Sertoli cells of the seminiferous tubules. Moreover, some connective tissue cells (compartmentalizing cells or Co-cells) of the intertubular space showed immunopositivity for CNPase, A2B5 and GalC. The results obtained show that Leydig cells of the human testis, in addition to their endocrine, neuronal and neuroendocrine features, possess qualities of both astrocytes and oligodendrocytes and thus show qualities of multipotential cells. Leydig cells probably differentiate to a phenotype that is characteristic for cells in the developing nervous system. Furthermore, the established immunohistochemical similarities are consistent with the assumption that foetal and postnatal Leydig cells are of common origin.

Desert Hedgehog/Patched 1 signaling specifies fetal Leydig cell fate in testis organogenesis

Establishment of the steroid-producing Leydig cell lineage is an event downstream of Sry that is critical for masculinization of mammalian embryos. Neither the origin of fetal Leydig cell precursors nor the signaling pathway that specifies the Leydig cell lineage is known. Based on the sex-specific expression patterns of Desert Hedgehog (Dhh) and its receptor Patched 1 (Ptch1) in XY gonads, we investigated the potential role of DHH/PTCH1 signaling in the origin and specification of fetal Leydig cells. Analysis of Dhh(-/-) XY gonads revealed that differentiation of fetal Leydig cells was severely defective. Defects in Leydig cell differentiation in Dhh(-/-) XY gonads did not result from failure of cell migration from the mesonephros, thought to be a possible source of Leydig cell precursors. Nor did DHH/PTCH1 signaling appear to be involved in the proliferation or survival of fetal Leydig precursors in the interstitium of the XY gonad. Instead, our results suggest that DHH/PTCH1 signaling triggers Leydig cell differentiation by up-regulating Steroidogenic Factor 1 and P450 Side Chain Cleavage enzyme expression in Ptch1-expressing precursor cells located outside testis cords.

Evidence that Sry is expressed in pre-Sertoli cells and Sertoli and granulosa cells have a common precursor

The expression of Sry in the undifferentiated, bipotential genital ridges of mammalian XY fetuses initiates testis development and is hypothesized to do so by directing supporting cell precursors to develop as Sertoli cells and not as granulosa cells. To directly test this hypothesis, transgenic mice expressing EGFP under the control of the Sry promoter were produced. After establishing that the transgene was expressed in fetal gonads similarly to endogenous Sry, the spatial and temporal expression of the Sry-EGFP transgene was investigated in developing gonads by using confocal microscopy and immunofluorescent histochemistry. This analysis indicated: (1) Sry is first expressed in cells located centrally in the genital ridge and then later in cells located at the cranial and caudal poles, (2) Sry is expressed exclusively in pre-Sertoli cells in the urogenital ridge, and (3) Sertoli and granulosa cells develop from a common precursor. These results support the hypothesis that Sry initiates testis differentiation by directing the development of supporting cell precursors as Sertoli rather than granulosa cells. Furthermore, the Sry expression pattern explains the nonrandom distribution of testicular and ovarian tissue in mammalian ovotestes.

Action of hormone responsive sequence in 2.3 kb promoter of CYP11A1

The CYP11A1 gene encodes cytochrome P450scc, the enzyme catalyzing the first step of steroid biosynthesis in the adrenal and gonad. We generated transgenic mice containing 2.3 kb of the 5'-flanking region of CYP11A1 driving LacZ reporter gene expression, in order to study hormonal control of CYP11A1 gene expression in different tissues. This 2.3 kb fragment contains information for hormonal control; by ACTH and hCG which increased reporter gene expression, in the adrenal and testis of transgenic mice respectively, while dexamethasone administration decreased reporter activity in the adrenal. The 5'-fragment of CYP11A1 has appreciable promoter activities in mouse adrenal Y1 cells but not in non-steroidogenic COS-1 cells, showing cell-type specificity. Transcription factor SF-1 activates the 2.3 kb promoter, which can be potentiated by cotransfection with c-Jun in steroidogenic JEG3 cells but not in COS-1 cells. We conclude that the 2.3 kb region of CYP11A1 contains elements controlling hormonal-dependent, cell-type-specific expression. In addition, c-Jun and SF-1 could act synergistically to activate CYP11A1 gene expression.

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.

Ectopic and abnormal hormone receptors in adrenal Cushing's syndrome

The mechanism by which cortisol is produced in adrenal Cushing's syndrome, when ACTH is suppressed, was previously unknown and was referred to as being "autonomous." More recently, several investigators have shown that some cortisol and other steroid-producing adrenal tumors or hyperplasias are under the control of ectopic (or aberrant, illicit, inappropriate) membrane hormone receptors. These include ectopic receptors for gastric inhibitory polypeptide (GIP), beta-adrenergic agonists, or LH/hCG; a similar outcome can result from altered activity of eutopic receptors, such as those for vasopressin (V1-AVPR), serotonin (5-HT4), or possibly leptin. The presence of aberrant receptors places adrenal cells under stimulation by a trophic factor not negatively regulated by glucocorticoids, leading to increased steroidogenesis and possibly to the proliferative phenotype. The molecular mechanisms responsible for the abnormal expression and function of membrane hormone receptors are still largely unknown. Identification of the presence of these illicit receptors can eventually lead to new pharmacological therapies as alternatives to adrenalectomy, now demonstrated by the long-term control of ectopic P-AR- and LH/hCGR-dependent Cushing's syndrome by propanolol and leuprolide acetate. Further studies will potentially identify a larger diversity of hormone receptors capable of coupling to G proteins, adenylyl cyclase, and steroidogenesis in functional adrenal tumors and probably in other endocrine and nonendocrine tumors.

Characterization of a proximal element in the rat preadipocyte factor-1 (Pref-1) gene promoter

Preadipocyte factor-1 (Pref-1) was shown to negatively regulate adipocyte differentiation. We recently reported that ZOG, a rat homolog of Pref-1, was specifically expressed in the adrenal zona glomerulosa. Results of the investigation of Pref-1 expression in preadipocyte and in undifferentiated adrenal cortex suggested that down-regulation of Pref-1 gene was closely correlated with the differentiation process. In this study we demonstrate that an upstream region (from -76 to -47) of the rat Pref-1 gene was essential for its expression in adrenocortical carcinoma-derived H295R cells. A nucleotide sequence found in this region, GCGTGGGCGTGGGCGGGGG (Egr/GC-box), seemed to contain three elements, two early growth response (Egr) elements and one GC-box, overlapping each other. Mutations of four or five nucleotides in a 7-nucleotides-stretch in the midst of the Egr/GC-box eliminated the binding of Sp1/3, abolished the activation by Egr-factor(s) and diminished the Pref-1 promoter activity. When mutations were introduced into the outside of the middle portion, the binding of Sp1/3 to the Egr/GC-box was abolished similarly. However, the decrease in the promoter activity was less than that found with the construct mutated at the middle. These results indicated that an element present at the 7-nucleotides-stretch in the midst of the Egr/GC-box might be important for the Pref-1 promoter activity, and this proximal element was possibly activated by a still-unidentified nuclear factor(s). This element would function as the promoter of the Pref-1 gene in H295R cells, but not in HeLa cells.

Identification of novel first exons in Ad4BP/SF-1 (NR5A1) gene and their tissue- and species-specific usage

It has been demonstrated that the mammalian Ad4BP/SF-1 (NR5A1) gene is regulated precisely in sex, tissue, and developmental stage specific manners. To clarify the complex transcriptional regulation, we investigated in the present study whether the gene transcription is regulated by multiple promoters accompanied by noncoding first exons. Novel first exons (Io and Ig) were identified downstream of the already identified exon Ia. Nucleotide sequences revealed that Ia and Ig exons were well conserved, whereas Io exon was less conserved among the mouse, rat, and human genes. Interestingly, the splice donor of the mouse and human Io and human Ig exons do not satisfy the consensus sequence. Transcripts containing Ia, Io, and Ig were detected in all rat tissues examined, while the transcript containing Io was undetectable in the corresponding tissues of mice. The lack of exon Io usage in the mouse was confirmed by transient transfection assays with cultured cells. Quantitative RT-PCR analysis revealed that the transcript containing Ig exon was the main product in the pituitary but significantly less in the spleen, suggesting that the regulation of Ad4BP/SF-1 gene transcription in the pituitary and spleen is distinct from that of other tissues. The above findings, together with the structural abnormality at the splice donor site, suggest that acquisition of the multiple first exons enables the Ad4BP/SF-1 gene to be regulated differentially in different animal species and in different tissues in the same animal.

Requirement of WT1 for gonad and adrenal development: insights from transgenic animals

Development of the gonad and adrenal gland occurs in close proximity and it has been proposed that they share a common primordium. Recent knockout and transgenic studies in mice have demonstrated that besides the orphan nuclear receptor SF1, the Wilms' tumor suppressor gene WT1 is important for gonad and adrenal gland development. WT1 is a complex gene with at least 24 isoforms produced from its locus. Although the role of each isoform is not yet understood, biochemical studies and analyses of human patients suggest that they do serve different functions in the cell. Here we present our current view of the part WT1 may play in the development of the gonad and discuss its possible role in the formation of the adrenal primordium.

Sex reversal caused by Mus musculus domesticus Y chromosomes linked to variant expression of the testis-determining gene Sry

When the Y chromosomes from certain populations of Mus musculus domesticus are introduced into the mouse strain C57BL/6 (B6), testis determination can fail, resulting in gonads developing either as ovotestes (with both ovarian and testicular components) or as ovaries. Not all Y(DOM) chromosomes cause sex reversal. Y(DOM) chromosomes are divided into three classes based upon their ability to induce testes in B6. The molecular basis underlying the three Y(DOM) classes is an enigma. The simplest explanation is that they harbor different alleles of the testis-determining gene, Sry. Sequencing of Sry(DOM) genes has indeed identified polymorphisms. However, none were unequivocally linked to the sex-reversal trait. It was concluded that all SRY(DOM) proteins are functionally equivalent. Using a semiquantitative RT-PCR assay, we now show that representatives of the three Y(DOM) classes have variant Sry expression patterns, that severity of sex reversal correlates with Sry mRNA titers, and that genetic correction of the sex reversal results in the upregulation of Sry expression. We propose that the variant Sry expression patterns result from polymorphisms at the site of a putative Sry enhancer.

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.

Gonadal and Extragonadal Functions of Ad4BP/SF-1: Developmental Aspects

Gene disruption studies have clearly indicated that 4-binding protein/steroidogenic factor 1 (Ad4BP/SF-1), originally identified as a steroidogenic tissue-specific transcription factor, plays crucial roles in the process of non-steroidogenic as well as steroidogenic tissue differentiation. Although the precise mechanisms underlying differentiation of these tissues are still under investigation, spatial and temporal expression profiles of the gene encoding Ad4BP/SF-1 support its contribution to tissue development from the earliest stages of ontogeny.

The renin-angiotensin system and the development of the kidney and adrenal in sheep

1. The earliest form of the kidney, the pronephros, does not really occur in the ovine embryo; instead, a giant glomerulus forms at the anterior end of the mesonephros. 2. In the sheep, the mesonephros is present from 11-38% of total gestation (150 days) and produces a dilute urine, as well as expressing the genes for erythropoietin, renin, angiotensinogen, angiotensin-converting enzyme and the angiotensin II (AngII) receptors AT1 and AT2. 3. The ovine metanephros begins to develop at 18% of gestation and nephrogenesis is complete several weeks before birth. All components of the renin-angiotensin system (RAS) are expressed from at least 27% of gestation. 4. Both AT1 and AT2 receptors are expressed by the adrenocortical cells early in gestation but, at mid-gestation, exogenous AngII does not stimulate aldosterone secretion in vivo. 5. Preliminary results suggest that AngII has important roles in renal development in the ovine foetus but the role(s), if any, in adrenal development, remains to be investigated.

Implication of ZOG protein (zona glomerulosa-specific protein) in zone development of the adrenal cortex

The three zones of adrenal cortex are thought to arise from a single multipotential stem cell. Immunohistochemical studies of fetal and adult adrenals using an antibody against a previously-cloned ZOG protein, a rat homolog of Pref-1, were conducted to explore its roles in the differentiation of cortical tissues. At the early embryonic stage, ZOG was already expressed in adrenogonadal primordial cells. The ZOG-positive cells gradually formed the adrenal primordium by E14.5. By E17.5 the expression was repressed in the inner part of the aggregate and these cells began to express CYP11B1. The ZOG-positive cells at this stage existed at the periphery of the aggregate but they did not express CYP11B2 yet. Not until E20.5 did the aldosteronogenic cells appear among the ZOG-positive cells at the outermost part of the gland. Based on these and the other findings the zonal development of the adrenal cortex is discussed.

Sex in the 90s: SRY and the switch to the male pathway

In mammals the male sex determination switch is controlled by a single gene on the Y chromosome, SRY. SRY encodes a protein with an HMG-like DNA-binding domain, which probably acts as a local organizer of chromatin structure. It is believed to regulate downstream genes in the sex determination cascade, although no direct targets of SRY are clearly known. More genes in the pathway have been isolated through mutation approaches in mouse and human. At least three genes, SRY itself, SOX9, and DAX1, are dosage sensitive, providing molecular evidence that the sex determination step operates at a critical threshold. SRY initiates development of a testis from the bipotential cells of the early gonad. The dimorphic male and female pathways present a rare opportunity to link a pivotal gene in development with morphogenetic mechanisms that operate to pattern an organ and the differentiation of its cells. Mechanisms of testis organogenesis triggered downstream of SRY include pathways of cell signaling controlling cell reorganization, cell proliferation, cell migration, and vascularization.

Polyadenylation-mediated translational regulation of maternal P450(11beta) mRNA in frog oocytes

Northern blot analysis of bullfrog tissues using a cDNA probe of cytochrome P450(11beta) showed that a large amount of message was present in the ovary as well as in the adrenal tissue. Two kinds of mRNA of different sizes were found in the ovary. Sequence determination of the two cDNAs and analysis by reverse-transcription polymerase chain reaction indicated that the protein encoded by the larger mRNA was identical to the adrenal enzyme, while the protein encoded by the smaller had a truncated sequence lacking an extension peptide necessary for the protein transport to the mitochondria. The mRNAs were present in the oocytes but not in the follicular cells, and their content in an oocyte varied little during its maturation. Immunoblot analyses of the mitochondrial fraction of oocytes failed to demonstrate the presence of P450(11beta) protein. In contrast the eggs were found to contain a large amount of enzymatically active protein. Interestingly the mRNA has a cis-element called cytoplasmic polyadenylation element at its 3' untranslated region. When poly(A) tails of the message prepared from eggs and oocytes were examined by RNase H digestion or reverse-transcription polymerase chain reaction, those of eggs were about 150 nucleotides longer than those of oocytes. These results suggest that translation of the message is stimulated during the oocyte maturation as a result of enhanced polyadenylation at its 3'-end. Finally a finding is presented that progesterone was converted to 11beta-hydroxyprogesterone by the frog P450(11beta), implying that the enzyme expressed in eggs may control a level of progesterone which is needed to initiate the oocyte maturation.

Developmental and functional biology of the primate fetal adrenal cortex

The unique characteristics of the primate (particularly human) fetal adrenal were first realized in the early 1900s when its morphology was examined in detail and compared with that of other species. The unusual architecture of the human fetal adrenal cortex, with its unique and disproportionately enlarged fetal zone, its compact definitive zone, and its dramatic remodeling soon after birth captured the interest of developmental anatomists. Many detailed anatomical studies describing the morphology of the developing human fetal adrenal were reported between 1920 and 1960, and these morphological descriptions have not changed significantly. More recently, it has become clear that fetal adrenal cortical growth involves cellular hypertrophy, hyperplasia, apoptosis, and migration and is best described by the migration theory, i.e. cells proliferate in the periphery, migrate centripetally, differentiate during their migration to form the functional cortical zones, and then likely undergo apoptosis in the center of the cortex. Consistent with this model, cells of intermediate phenotype, arranged in columnar cords typical of migration, have been identified between the definitive and fetal zones. This cortical area has been referred to as the transitional zone and, based on the expression of steroidogenic enzymes, we consider it to be a functionally distinct cortical zone. Elegant experiments during the 1950s and 1960s demonstrated the central role of the primate fetal adrenal cortex in establishing the estrogenic milieu of pregnancy. Those findings were among the first indications of the function and physiological role of the human fetal adrenal cortex and led Diczfalusy and co-workers to propose the concept of the feto-placental unit, in which DHEA-S produced by the fetal adrenal cortex is used by the placenta for estrogen synthesis. Tissue and cell culture techniques, together with improved steroid assays, revealed that the fetal zone is the primary source of DHEA-S, and that its steroidogenic activity is regulated by ACTH. In recent years, function of the human and rhesus monkey fetal adrenal cortical zones has been reexamined by assessing the localization and ontogeny of steroidogenic enzyme expression. The primate fetal adrenal cortex is composed of three functionally distinct zones: 1) the fetal zone, which throughout gestation does not express 3 beta HSD but does express P450scc and P450c17 required for DHEA-S synthesis; 2) the transitional zone, which early in gestation is functionally identical to the fetal zone but late in gestation (after 25-30 weeks) expresses 3 beta HSD, P450scc, and P450c17, and therefore is the likely site of glucocorticoid synthesis, and 3) the definitive zone, which lacks P450c17 throughout gestation but late in gestation (after 22-24 weeks) expresses 3 beta HSD and P450scc, and therefore is the likely site of mineralocorticoid synthesis. Indirect evidence, based on effects of P450c21 deficiency and maternal estriol concentrations, indicate that the fetal adrenal cortex produces cortisol and DHEA-S early in gestation (6-12 weeks). However, controversy exists as to whether cortisol is produced de novo or derived from the metabolism of progesterone, as data regarding the expression of 3 beta HSD in the fetal adrenal cortex early in gestation are conflicting. During the 1960s, Liggins and colleagues demonstrated that in the sheep, cortisol secreted by the fetal adrenal cortex late in gestation regulates maturation of the fetus and initiates the cascade of events leading to parturition. Those pioneering discoveries provided insight into the mechanism underlying the timing of parturition and therefore were of particular interest to obstetricians and perinatologists confronted with the problems of preterm labor. However, although cortisol emanating from the fetal adrenal cortex promotes fetal maturation in primates as it does in sheep, its role in the regulation of primate parturition, unlike that in sheep