Delta-frequency stimulation of cerebellar projections can compensate for schizophrenia-related medial frontal dysfunction

Schizophrenia involves abnormalities in the medial frontal cortex that lead to cognitive deficits. Here we investigate a novel strategy to normalize medial frontal brain activity by stimulating cerebellar projections. We used an interval timing task to study elementary cognitive processing that requires both frontal and cerebellar networks that are disrupted in patients with schizophrenia. We report three novel findings. First, patients with schizophrenia had dysfunctional delta rhythms between 1-4 Hz in the medial frontal cortex. We explored cerebellar-frontal interactions in animal models and found that both frontal and cerebellar neurons were modulated during interval timing and had delta-frequency interactions. Finally, delta-frequency optogenetic stimulation of thalamic synaptic terminals of lateral cerebellar projection neurons rescued timing performance as well as medial frontal activity in a rodent model of schizophrenia-related frontal dysfunction. These data provide insight into how the cerebellum influences medial frontal networks and the role of the cerebellum in cognitive processing.

Prefrontal D1 dopamine signaling is necessary for temporal expectation during reaction time performance

Responses during a simple reaction time task are influenced by temporal expectation, or the ability to anticipate when a stimulus occurs in time. Here, we test the hypothesis that prefrontal D1 dopamine signaling is necessary for temporal expectation during simple reaction time task performance. We depleted dopamine projections to the medial prefrontal circuits by infusing 6-hydroxidopamine, a selective neurotoxin, into the ventral tegmental area (VTA) of rats, and studied their performance on a simple reaction time task with two delays. VTA dopamine depletion did not change movements or learning of the reaction time task. However, VTA dopamine-depleted animals did not develop delay-dependent speeding of reaction times, suggesting that mesocortical dopamine signaling is required for temporal expectation. Next, we manipulated dopamine signaling within the medial prefrontal cortex using local pharmacology. We found that SCH23390, a D1-type dopamine receptor antagonist, specifically attenuated delay-dependent speeding, while sulpiride, a D2-type receptor antagonist, did not. These data suggest that prefrontal D1 dopamine signaling is necessary for temporal expectation during performance of a simple reaction time task. Our findings provide insight into temporal processing of the prefrontal cortex, and how dopamine signaling influences prefrontal circuits that guide goal-directed behavior.

Long-term safety of recombinant human growth hormone in children

BACKGROUND

Between 1985 and 2006, the National Cooperative Growth Study (NCGS) monitored the safety and efficacy of recombinant human growth hormone (rhGH) in 54,996 children.

METHODS

Enrolled patients were followed until rhGH discontinuation. Investigators submitted adverse event reports for targeted events or those potentially rhGH-related.

RESULTS

Early concerns about de novo leukemia in patients without risk factors have not been substantiated--three observed vs. 5.6 expected in age-matched general population based on years at risk [standard incidence ratio (SIR), 0.54; 95% confidence interval (CI), 0.11-1.58]. De novo malignancies (intracranial and extracranial) were not significantly increased in patients without risk factors (29 confirmed vs. 26 expected; SIR, 1.12; 95% CI, 0.75-1.61). Second neoplasms occurred in 49 patients, of whom 37 had irradiation for their initial tumors (including five of 16 retinoblastoma patients, three of whom had bilateral retinoblastoma) consistent with an increased risk with rhGH. Thirty-three patients developed type 1 diabetes mellitus (DM) (37 expected; SIR, 0.90; 95% CI, 0.62-1.26). Type 2 DM and nonspecified DM were reported in 20 and eight patients, respectively. Two deaths were reported in patients with Prader-Willi syndrome and five deaths from aortic dissection in patients with Turner syndrome. In patients with organic GH deficiency and idiopathic panhypopituitarism, 11 events of acute adrenal insufficiency occurred, including four deaths, consistent with a reported increased risk for adrenal insufficiency in hypopituitary patients with or without rhGH treatment.

CONCLUSION

After more than 20 yr, leukemia, a major safety issue initially believed associated with GH, has not been confirmed, but other signals, including risk of second malignancies in patients previously treated with irradiation, have been detected or confirmed through the NCGS. These data further clarify the events associated with rhGH and, although confirming a favorable overall safety profile, they also highlight specific populations at potential risk.

Variation in the seasonal selection of resources by woodland caribou in northern British Columbia

Conservation planning for species of concern or importance can be aided by resource selection functions (RSFs) that identify important areas or attributes. Models that can be interpreted biologically and provide reasonable predictive capacity may best be based on data from individuals grouped into seasonal selection strategies for particular geographical areas or similarities in topographical and vegetative associations. We used logistic regression, the information–theoretic approach, satellite imagery, and locational data (n = 31 females; 16 803 locations) from global positioning system (GPS) collared woodland caribou ( Rangifer tarandus caribou (Gmelin, 1788)) to model resource selection by animals during calving, summer, fall, breeding, winter, and late-winter seasons. Higher variation in resource use corresponded to times when caribou and their young were most susceptible to predation or when food resources were limited. Even with multiple selection strategies, caribou followed a general progression from higher to lower elevation habitats from calving and summer to late winter. Caribou selected against or completely avoided the burned–disturbed vegetation class in every season except summer. We incorporated RSFs with a raster geographic information system to create selection landscapes. We validated selection landscapes using withheld GPS data (n = 6077), 50 known calving sites, and Spearman’s rank correlation coefficient. Selection models and final selection landscapes performed well in validating use locations of woodland caribou in all seasons (all P < 0.003) and in predicting known calving sites (P < 0.001). When seasonal selection strategies are identified and models are coupled with validation, RSFs are effective tools to assist in conservation planning.

Combined haploinsufficiency of SF-1 and GATA4 does not reveal a genetic interaction in mouse gonadal development

The nuclear receptor steroidogenic factor 1 (SF-1 or NR5A1) and the zinc finger protein GATA4 mediate key events in the early steps of gonadal development and sex differentiation, presumably by activating the expression of essential target genes. An important SF-1 target in male sex differentiation is the gene encoding the anti-Müllerian hormone (AMH), which induces regression of the Müllerian ducts in the developing male embryo. In cell transfection studies, there is apparent cooperation between GATA4 and SF-1 in the regulation of both human and mouse Amh promoters. We hypothesized that compound haploinsufficiency of both SF-1 and GATA4, by reducing their synergism, might cause a more severe phenotype than that seen in mice that were heterozygous for either SF-1 or Gata4 alone. Surprisingly, in adult and embryonic mice, compound haploinsufficiency of SF-1 and GATA4 caused no gonadal or reproductive abnormalities beyond those seen in SF-1(+/-) mice. Thus, although cooperation between SF-1 and GATA4 very likely is important for regulation of their target genes, such synergy was not revealed in our in vivo studies of gonadal development and function.

Pituitary-specific knockout of steroidogenic factor 1

Knockout mice lacking the orphan nuclear receptor steroidogenic factor 1 (SF-1) revealed its essential roles at multiple levels of endocrine development and function. These SF-1 knockout mice lacked adrenal glands and gonads, thereby manifesting adrenal insufficiency and sex reversal of their internal and external genitalia. Their pituitary gonadotropes failed to express several markers of normal differentiated function, and they lacked a specific hypothalamic nucleus, the ventromedial hypothalamic nucleus (VMH). Using the Cre-loxP system, we generated mice whose gene encoding SF-1 was inactivated specifically in the anterior pituitary. These pituitary-specific SF-1 knockout mice were sterile and never matured sexually. Their gonads weighed only approximately 5% of the weight of wild-type gonads. SF-1 immunoreactivity was absent in the anterior pituitary but was unaffected in the adrenal cortex, validating the selectivity of the gene targeting strategy. Consistent with an important role of SF-1 in gonadotropes, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were markedly decreased in the pituitary-specific SF-1 knockout mice. The pituitary-specific SF-1 knockout mice are a novel genetic model of hypogonadotropic hypogonadism and establish essential roles of SF-1 in gonadotropin expression.

Approaches to define the role of SF-1 at different levels of the hypothalamic-pituitary-steroidogenic organ axis

Targeted gene disruption has produced knockout mice lacking the orphan nuclear receptor steroidogenic factor 1 (SF-1). These SF-1 knockout mice lacked adrenal glands and gonads, resulting in adrenocortical insufficiency and sex reversal of their internal and external genitalia. They also had impaired expression of pituitary gonadotropins and agenesis of the ventromedial hypothalamic nucleus (VMH), confirming roles of SF-1 at multiple levels of the hypothalamic-pituitary-steroidogenic tissue axis. Using the Cre-loxP system, we now have generated mice in which SF-1 is inactivated selectively in the anterior pituitary. These pituitary-specific SF-1 knockout mice were sterile and failed to exhibit sexual maturation. Histologically, their gonads were markedly hypoplastic, weighing only approximately 5% of the gonads of wild-type mice. Consistent with an important role of SF-1 in gonadotropes, there were no cells in the pituitary gland that expressed either follicle-stimulating hormone (FSH) or luteinizing hormone (LH). These pituitary-specific SF-1 knockout mice are a novel genetic model of hypogonadotropic hypogonadism and establish essential roles of SF-1 in gonadotropin expression.

Hypomorphic phenotype in mice with pituitary-specific knockout of steroidogenic factor 1

The bacteriophage Cre recombinase provides a powerful approach for tissue-specific gene inactivation. Using a Cre transgene driven by the common alpha subunit of glycoprotein hormones (alphaGSU-Cre), we have previously inactivated steroidogenic factor 1 (SF-1) in the anterior pituitary, causing hypogonadotropic hypogonadism with sexual infantilism, sterility, and severe gonadal hypoplasia. We now explore the molecular mechanisms underlying a hypomorphic gonadal phenotype in mice carrying two floxed SF-1 alleles (F/F) relative to mice carrying one recombined and one floxed allele (F/R). Because their Cre-mediated disruption of the locus encoding SF-1 was less efficient, alphaGSU-Cre, F/F mice retained some gonadotropin-expressing cells in the anterior pituitary, thereby stimulating some gonadal function. This novel in vivo model for exploring the effects of differing levels of gonadotropins on gonadal development highlights the need for careful genotype-phenotype comparisons in studies using Cre recombinase to produce tissue-specific knockouts.

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.

TFIIAalpha/beta-like factor is encoded by a germ cell-specific gene whose expression is up-regulated with other general transcription factors during spermatogenesis in the mouse

TFIIAalpha/beta-like factor (ALF) is a testis-specific counterpart of the large subunit of human general transcription factor TFIIA. Northern analysis shows that ALF mRNA first appears in mouse testis at Postnatal Day 14. Similarly, expression of the general transcription factors TBP, TRF2, TFIIAalpha/beta, TFIIAgamma, and TFIIIB(90) is also increased beginning at Postnatal Day 14, suggesting that there is a coordinated induction of many general transcription factors during male germ cell differentiation. Analysis of male germ cells separated by Staput sedimentation shows that ALF is present in pachytene spermatocytes and haploid spermatids. In addition, in situ hybridization experiments with adult mouse testis shows that ALF is present in haploid spermatids. Searches of the human genome sequence database using the basic local alignment search tool reveal that the ALF and TFIIAalpha/beta(GTF2A1) genes are both composed of nine exons, whereas the TFIIAgamma (GTF2A2) gene is composed of five exons. Furthermore, nucleotide and amino acid comparisons among human and mouse ALF, TFIIAalpha/beta, and TFIIAgamma cDNA sequences show that ALF has diverged more rapidly than either TFIIAalpha/beta or TFIIAgamma. Finally, the ALF and SBLF (Stoned B-Like Factor) sequences present in the chimeric SALF cDNA are both present on human chromosome 2, and an analysis of the corresponding genes suggests a model for the formation of SALF.

SF-1: a critical mediator of steroidogenesis

Studies in knockout mice have established that the orphan nuclear receptor steroidogenic factor 1 (SF-1) plays essential roles in the development and function of the primary steroidogenic organs. These SF-1 knockout mice lacked adrenal glands and gonads, causing adrenocortical insufficiency and sex reversal of their internal and external genitalia. They also had impaired expression of pituitary gonadotropins and agenesis of the ventromedial hypothalamic nucleus (VMH), confirming roles of SF-1 at all three levels of the hypothalamic-pituitary-steroidogenic organ axis. Ongoing experiments are directed at developing methods to inactivate SF-1 in a tissue-specific manner.

Steroidogenic factor 1 (SF1) is essential for pituitary gonadotrope function

Knockout mice lacking the orphan nuclear receptor steroidogenic factor 1 (SF1) exhibit a complex endocrine phenotype that includes adrenal and gonadal agenesis, impaired expression of pituitary gonadotropins, and absence of the ventromedial hypothalamic nucleus (VMH). These multiple defects complicate efforts to delineate primary versus secondary effects of SF1 deficiency in different tissues, such that its direct role in gonadotropes remains uncertain. To define this role, we have expressed Cre recombinase driven by the promoter region of the common alpha subunit of glycoprotein hormones (alpha GSU), thereby inactivating a loxP-modified SF1 locus in the anterior pituitary gland. Although pituitary-specific SF1 knockout mice were fully viable, they were sterile and failed to develop normal secondary sexual characteristics. Their adrenal glands and VMH appeared normal histologically, but their testes and ovaries were severely hypoplastic. alpha GSU-Cre, loxP mice had normal levels of most pituitary hormones, but had markedly decreased expression of LH and FSH. Treatment with exogenous gonadotropins stimulated gonadal steroidogenesis, inducing germ cell maturation in males and follicular and uterine maturation in females--establishing that the gonads can respond to gonadotropins. The pituitary-specific SF1 knockout mice are a novel genetic model of hypogonadotropic hypogonadism that establishes essential role(s) of SF1 in pituitary gonadotropes.

Expression profiles of SF-1, DAX1, and CYP17 in the human fetal adrenal gland: potential interactions in gene regulation

Cytochrome P450 17alpha-hydroxylase/17-20 lyase (P450(C17)) is a critical branchpoint enzyme for steroid hormone biosynthesis. During human gestation, P450(C17) is required for the production of dehydroepiandrostenedione sulfate by the fetal adrenal cortex and for testicular production of androgens that mediate male sexual differentiation. In this study, we investigate the regulation of the human CYP17 gene by two orphan nuclear receptors, steroidogenic factor 1 (SF-1) and DAX1. In human embryos, SF-1 and DAX1 are expressed throughout the developing adrenal cortex from its inception at 33 days post conception (dpc). In contrast, P450(C17) expression, which commences between 41 and 44 dpc, is limited to the fetal zone. The 5'-flanking region of the human CYP17 gene contains three functional SF-1 elements that collectively mediate a > or =25-fold induction of promoter activity by SF-1. In constructs containing all three functional SF-1 elements, DAX1 inhibited this activation by > or =55%. In the presence of only one or two SF-1 elements, DAX1 inhibition was lost even though SF-1 transactivation persisted. These data suggest that efficient repression of SF-1-mediated activation of the human CYP17 gene by DAX1 requires multiple SF-1 elements. Opposing effects of SF-1 and DAX1 may fine tune the differential responses of various SF-1 target genes in different endocrine tissues.

Approaches to define the role of SF-1 at different levels of the hypothalamic-pituitary-steroidogenic organ axis

Targeted gene disruption has produced knockout mice globally deficient in the orphan nuclear receptor steroidogenic factor 1 (SF-1). These SF-1 knockout mice lacked adrenal glands and gonads and consequently exhibited adrenocortical insufficiency and sex reversal of their internal and external genitalia. They also had impaired expression of gonadtropins in the anterior pituitary gonadotropes and agenesis of the ventromedial hypothalamic nucleus (VMH), confirming roles of SF-1 at all three levels of the hypothalamic-pituitary-steroidogenic organ axis. Ongoing experiments are directed at using evolving techniques for tissue-specific gene inactivation to define the roles of SF-1 within discrete sites of the hypthalamic-pituitary-steroidogenic organ axis.

Developmental roles of the steroidogenic acute regulatory protein (StAR) as revealed by StAR knockout mice

Steroidogenic acute regulatory protein (StAR) is essential for adrenal and gonadal steroidogenesis, stimulating the translocation of cholesterol to the inner mitochondrial membrane where steroidogenesis commences. StAR mutations in humans cause congenital lipoid adrenal hyperplasia (lipoid CAH), an autosomal recessive condition with severe deficiencies of all classes of steroid hormones. We previously described StAR knockout mice that mimic many features of lipoid CAH patients. By keeping StAR knockout mice alive with corticosteroid replacement, we now examine the temporal effects of StAR deficiency on the structure and function of steroidogenic tissues. The adrenal glands, affected most severely at birth, exhibited progressive increases in lipid deposits with aging. The testes of newborn StAR knockout mice contained scattered lipid deposits in the interstitial region, presumably in remnants of fetal Leydig cells. By 8 weeks of age, the interstitial lipid deposits worsened considerably and were associated with Leydig cell hyperplasia. Despite these changes, germ cells in the seminiferous tubules appeared intact histologically, suggesting that the StAR knockout mice retained some capacity for androgen biosynthesis. Sperm maturation was delayed, and the germ cells exhibited histological features of apoptosis, consistent with suboptimal androgen production. Immediately after birth, the ovaries of StAR knockout mice appeared normal. After the time of normal puberty, however, prominent lipid deposits accumulated in the interstitial region, accompanied by marked luteinization of stromal cells and incomplete follicular maturation that ultimately culminated in premature ovarian failure. These studies provide the first systematic evaluation of the developmental consequences of StAR deficiency in the various steroidogenic organs.

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

The orphan nuclear receptor steroidogenic factor 1 (SF-1) was identified originally as a key regulator of the tissue-specific expression of the cytochrome P450 steroid hydroxylases. Hints at considerably broader roles for SF-1 came from analyses of its expression pattern in mouse embryos. As anticipated, SF-1 was expressed in the adrenal glands and gonads from their early stages of development. Surprisingly, SF-1 also was expressed outside of the primary steroidogenic tissues in the anterior pituitary and hypothalamus. SF-1 knockout mice dramatically confirmed its multiple essential roles in vivo. These mice lacked adrenal glands and gonads, leading to adrenocortical insufficiency and male-to-female sex reversal of their internal and external genitalia. SF-1 knockout mice also had impaired pituitary expression of gonadotropins and agenesis of the ventromedial hypothalamic nucleus (VMH), confirming roles of SF-1 at all three levels of the hypothalamic-pituitary-gonadal axis. With some focus on the ovary, this review summarizes experiments that have defined essential roles of SF-1 in endocrine development, and highlights important areas for future studies.

The LIM homeobox gene Lhx9 is essential for mouse gonad formation

During mammalian embryonic development, the ovaries and testes develop from somatic cells of the urogenital ridges as indifferent gonads, harbouring primordial germ cells that have migrated there. After sex determination of the gonads, the testes produce testosterone and anti-Mullerian hormone which mediate male sexual differentiation, and the female developmental pathway ensues in their absence. Here we show that transcripts of the LIM homeobox gene Lhx9 are present in urogenital ridges of mice at embryonic day 9.5; later they localize to the interstitial region as morphological differentiation occurs. In mice lacking Lhx9 function, germ cells migrate normally, but somatic cells of the genital ridge fail to proliferate and a discrete gonad fails to form. In the absence of testosterone and anti-Mullerian hormone, genetically male mice are phenotypically female. The expression of steroidogenic factor 1 (Sf1), a nuclear receptor essential for gonadogenesis, is reduced to minimal levels in the Lhx9-deficient genital ridge, indicating that Lhx9 may lie upstream of Sf1 in a developmental cascade. Unlike mice lacking other genes that mediate early stages of gonadogenesis, Lhx9 mutants do not exhibit additional major developmental defects. Thus, LHX9 mutations may underlie certain forms of isolated gonadal agenesis in humans.

Developmental and hormonal regulation of murine scavenger receptor, class B, type 1

The scavenger receptor, class B, type I (SR-BI), is the predominant receptor that supplies plasma cholesterol to steroidogenic tissues in rodents. We showed previously that steroidogenic factor-1 (SF-1) binds a sequence in the human SR-BI promoter whose integrity is required for high-level SR-BI expression in cultured adrenocortical tumor cells. We now provide in vivo evidence that SF-1 regulates SR-BI. During mouse embryogenesis, SR-BI mRNA was initially expressed in the genital ridge of both sexes and persisted in the developing testes but not ovary. This sexually dimorphic expression profile of SR-BI expression in the gonads mirrors that of SF-1. No SR-BI mRNA was detected in the gonadal ridge of day 11.5 SF-1 knockout embryos. Both SR-BI and SF-1 mRNA were expressed in the cortical cells of the nascent adrenal glands. These studies directly support SF-1 participating in the regulation of SR-BI in vivo. We examined the effect of cAMP on SR-BI mRNA and protein in mouse adrenocortical (Y1-BS1) and testicular carcinoma Leydig (MA-10) cells. The time courses of induction were strikingly similar to those described for other cAMP- and SF-1-regulated genes. Addition of lipoproteins reduced SR-BI expression in Y1-BS1 cells, an effect that was reversed by administration of cAMP analogs. SR-BI mRNA and protein were expressed at high levels in the adrenal glands of knockout mice lacking the steroidogenic acute regulatory protein; these mice have extensive lipid deposits in the adrenocortical cells and high circulating levels of ACTH. Taken together, these studies suggest that trophic hormones can override the suppressive effect of cholesterol on SR-BI expression, thus ensuring that steroidogenesis is maintained during stress.

Expression of steroidogenic factor 1 and Wilms' tumour 1 during early human gonadal development and sex determination

The transcription factors SF-1 and WT1 play pivotal roles in mammalian gonadal development and sexual differentiation. In human embryos, both SF-1 and WT1 are expressed when the indifferent gonadal ridge first forms at 32 days post-ovulation. As the sex cords develop - providing morphological evidence of testis differentiation - SF-1 localises predominantly to developing Sertoli cells in the sex cords, whereas WT1 retains a broader pattern of expression. Later, SF-1 localises predominantly to steroidogenic Leydig cells, and WT1 localises to the sex cords. In the ovary, SF-1 and WT1 transcripts persist in the gonadal ridge from the earliest developmental stages throughout the critical period of sex determination. These studies, which delineate for the first time the sequential expression profiles of SF-1 and WT1 during human gonadal development, provide a framework for understanding human sex reversal phenotypes associated with their mutations.

Activation of the promoter of the orphan receptor SHP by orphan receptors that bind DNA as monomers

Small heterodimer partner (SHP) is an orphan nuclear receptor that lacks a conventional DNA binding domain. It interacts with several other members of the nuclear receptor superfamily and inhibits receptor transactivation. In order to characterize the regulation of SHP expression, a number of receptors and other transcription factors were tested for effects on the SHP promoter. Among these, the orphan receptor steroidogenic factor-1 (SF-1) was found to potently transactivate the SHP promoter. Detailed footprinting studies show that the SHP promoter contains at least five SF-1 binding sites, and mutagenesis studies demonstrate each of the three strongest binding sites is required for SF-1 transactivation. SHP is coexpressed with SF-1 in adrenal glands, but is also expressed in tissues that lack SF-1, including liver. However, liver expresses a close relative of SF-1, the orphan fetoprotein transcription factor (FTF), and FTF can also transactivate the SHP promoter. These results suggest that alterations in the levels or activities of SF-1 or FTF could modulate SHP expression in appropriate tissues and thereby affect a variety of receptor dependent signaling pathways.

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 paper 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.

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

Steroidogenic factor 1 (SF-1), an orphan nuclear receptor, initially was isolated as a key regulator of the tissue-specific expression of the cytochrome P450 steroid hydroxylases. Thereafter, analyses of sites of SF-1 expression during mouse embryological development hinted at considerably expanded roles for SF-1, roles that were strikingly confirmed through the analyses of SF-1 knockout mice. These SF-1 knockout mice exhibited adrenal and gonadal agenesis, associated with male-to-female sex reversal of their internal and external genitalia and death from adrenocortical insufficiency. These findings showed unequivocally that SF-1 is essential for the embryonic survival of the primary steroidogenic organs. SF-1 knockout mice also had impaired pituitary expression of gonadotropins and agenesis of the ventromedial hypothalamic nucleus (VMH), establishing that SF-1 regulates reproductive function at all three levels of the hypothalamic-pituitary gonadal axis. This article reviews the experiments that have defined these essential roles of SF-1 in endocrine development and highlights important areas for future studies.

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 roles of steroidogenic factor 1 in endocrine development and function

The orphan nuclear receptor steroidogenic factor 1 (SF-1) was initially isolated as a key regulator of the cytochrome P450 steroid hydroxylases in adrenocortical and gonadal cells. Subsequent analyses of SF-1 knockout mice have expanded considerably our understanding of the roles that SF-1 plays in endocrine development. These SF-1 knockout mice lacked adrenal glands and gonads, with consequent male-to-female sex reversal of their internal and external genitalia. Thus, SF-1 is essential for the embryonic survival of the primary steroidogenic organs. They further exhibited impaired gonadotrope function and agenesis of the ventromedial hypothalamic nucleus, establishing that SF-1 contributes to reproductive function at all three levels of the hypothalamic-pituitary-gonadal axis. This report reviews experiments that have defined these critical roles of SF-1 in endocrine development, and highlights areas of ongoing investigation.

Targeted disruption of StAR provides novel insights into congenital adrenal hyperplasia

To explore the function of StAR in a system that can be experimentally manipulated, and to develop a mouse model for the human disorder lipoid congenital adrenal hyperplasia (lipoid CAH), we used targeted gene disruption to produce a mouse line deficient in StAR protein. Initially, StAR knockout mice were indistinguishable from wildtype littermates, except that all had female external genitalia. After birth, they showed signs of either respiratory distress or volume depletion and eventually died. Hormone assays confirmed severe defects in adrenal steroids, whereas hormones constituting the gonadal axis did not differ significantly from levels in wildtype littermates. Histologically, the adrenal cortex of StAR knockout mice contained florid lipid deposits, as visualized with oil red O stain. Lesser lipid deposits were observed in the steroidogenic compartment of the testis and none in the ovary. The sex-specific differences in gonadal involvement provide evidence for a two-stage model of the pathogenesis of StAR deficiency, with trophic hormone stimulation causing progressive accumulation of lipids within the steroidogenic cells which ultimately kills them. These StAR knockout mice provide a novel system in which to study StAR's essential roles in adrenocortical and gonadal steroidogenesis.

The roles of steroidogenic factor 1 in endocrine development and function

The nuclear hormone receptor family--structurally-related transcriptional regulators that mediate the actions of steroid hormones, thyroid hormone, vitamin D, and retinoids--also includes orphan members that lack known activating ligands. One of these orphan receptors, steroidogenic factor 1 (SF-1), has recently been shown to play key roles in steroidogenic cell function within the adrenal cortex and gonads. SF-1 also contributes to reproductive function at all three levels of the hypothalamic-pituitary-gonadal axis. Key insights into these roles came from analyses of SF-1 knockout mice, which revealed adrenal and gonadal agenesis with consequent male-to-female sex reversal of their internal and external genitalia, impaired gonadotrope function, and agenesis of the ventromedial hypothalamic nucleus. This report reviews the data that have established SF-1 as a critical mediator of endocrine differentiation and function.

Structure and localization of the human gene encoding SR-BI/CLA-1. Evidence for transcriptional control by steroidogenic factor 1

The scavenger receptor, class B, type 1 receptor (SR-BI) mediates the selective transport of lipids from high density lipoprotein to cells. We describe the structure and subchromosomal location of human SR-BI and provide evidence that it is regulated by the transcription factor, steroidogenic factor 1 (SF-1). SR-BI resides on chromosome 12q24.2-qter, spans approximately 75 kilobase pairs, and contains 13 exons. RNA blot analysis of human tissues reveals an expression pattern similar to that described previously for rodents with the highest levels of mRNA in the adrenal gland, ovary, and liver. Unlike rodents, human SR-BI was expressed at high levels in the placenta. The transcription start site for SR-BI was mapped, and DNA sequence analysis revealed a binding site for SF-1 in the proximal 5'-flanking sequence. SF-1, an orphan member of the nuclear hormone receptor gene family, plays a key role in the regulation of steroidogenesis and is expressed at high levels in steroidogenic tissues. SF-1 binds to the SR-BI promoter in a sequence-specific manner, and efficient transcription from this promoter in adrenocortical Y1 cells is dependent on an intact SF-1 site. These data extend our understanding of SF-1 function within steroidogenic tissues and suggest that SR-BI, which serves to supply selected tissues with lipoprotein-derived lipids, is part of the repertoire of SF-1-responsive genes involved in steroidogenesis.

Targeted disruption of the mouse gene encoding steroidogenic acute regulatory protein provides insights into congenital lipoid adrenal hyperplasia

An essential component of regulated steroidogenesis is the translocation of cholesterol from the cytoplasm to the inner mitochondrial membrane where the cholesterol side-chain cleavage enzyme carries out the first committed step in steroidogenesis. Recent studies showed that a 30-kDa mitochondrial phosphoprotein, designated steroidogenic acute regulatory protein (StAR), is essential for this translocation. To allow us to explore the roles of StAR in a system amenable to experimental manipulation and to develop an animal model for the human disorder lipoid congenital adrenal hyperplasia (lipoid CAH), we used targeted gene disruption to produce StAR knockout mice. These StAR knockout mice were indistinguishable initially from wild-type littermates, except that males and females had female external genitalia. After birth, they failed to grow normally and died from adrenocortical insufficiency. Hormone assays confirmed severe defects in adrenal steroids-with loss of negative feedback regulation at hypothalamic-pituitary levels-whereas hormones constituting the gonadal axis did not differ significantly from levels in wild-type littermates. Histologically, the adrenal cortex of StAR knockout mice contained florid lipid deposits, with lesser deposits in the steroidogenic compartment of the testis and none in the ovary. The sex-specific differences in gonadal involvement support a two-stage model of the pathogenesis of StAR deficiency, with trophic hormone stimulation inducing progressive accumulation of lipids within the steroidogenic cells and ultimately causing their death. These StAR knockout mice provide a useful model system in which to determine the mechanisms of StAR's essential roles in adrenocortical and gonadal steroidogenesis.

Germ cell nuclear antigen (GCNA1) expression does not require a gonadal environment or steroidogenic factor 1: examination of GCNA1 in ectopic germ cells and in Ftz-F1 null mice

The germ cell lineage is first recognized as a population of mitotically proliferating primordial germ cells that migrate toward the gonadal ridge. Shortly after arriving at the gonadal ridge, the germ cells begin to initiate a commitment to gamete production in the developing gonad. The mechanisms controlling this transition are poorly understood. We recently reported that a mouse germ cell nuclear antigen 1 (GCNA1) is initially detected in both male and female germ cells as they reach the gonad at 11.5 days postcoitum (dpc). GCNA1 is continually expressed in germ cells through all stages of gametogenesis until the diplotene/dictyate stage of meiosis I. Since GCNA1 expression commences soon after primordial germ cells arrive at the gonadal ridge, we wanted to determine whether the gonadal environment was essential for induction of GCNA1 expression. By examining GCNA1 expression in germ cells that migrate ectopically into the adrenal gland, we determined that both the gonadal and adrenal gland environments allow GCNA1 expression. We also examined GCNA1 expression Ftz-F1 null mice, which were born lacking gonads and adrenal glands. During embryonic development in the Ftz-F1 null mice, the gonad and most germ cells undergo apoptotic degeneration at about 12.5 dpc. While most of the germ cells undergo apoptosis without expressing GCNA1, a few surviving germs cells, especially outside the involuting gonad clearly express GCNA1. Thus, although the Ftz-F1 gene is essential for gonadal and adrenal development, induction of GCNA1 expression in germ cells does not require Ftz-F1 gene products. The finding that germ cell GCNA1 expression is not restricted to the gonadal environment and is not dependent on the Ftz-F1 gene products suggests that GCNA1 expression may be initiated in the germ cell lineage by autonomous means.

Activation of the orphan nuclear receptor steroidogenic factor 1 by oxysterols

Steroidogenic factor 1 (SF-1), an orphan member of the intracellular receptor superfamily, plays an essential role in the development and function of multiple endocrine organs. It is expressed in all steroidogenic tissues where it regulates the P450 steroidogenic genes to generate physiologically active steroids. Although many of the functions of SF-1 in vivo have been defined, an unresolved question is whether a ligand modulates its transcriptional activity. Here, we show that 25-, 26-, or 27-hydroxycholesterol, known suppressors of cholesterol biosynthesis, enhance SF-1-dependent transcriptional activity. This activation is dependent upon the SF-1 activation function domain, and, is specific for SF-1 as several other receptors do not respond to these molecules. The oxysterols activate at concentrations comparable to those previously shown to inhibit cholesterol biosynthesis, and, can be derived from cholesterol by P450c27, an enzyme expressed within steroidogenic tissues. Recent studies have shown that the nuclear receptor LXR also is activated by oxysterols. We demonstrate that different oxysterols differ in their rank order potency for these two receptors, with 25-hydroxycholesterol preferentially activating SF-1 and 22(R)-hydroxycholesterol preferentially activating LXR. These results suggest that specific oxysterols may mediate transcriptional activation via different intracellular receptors. Finally, ligand-dependent transactivation of SF-1 by oxysterols may play an important role in enhancing steroidogenesis in vivo.

Characterization of the promoter region of the mouse gene encoding the steroidogenic acute regulatory protein

Steroidogenic acute regulatory protein (StAR) delivers cholesterol to the inner mitochondrial membrane, where the cholesterol side-chain cleavage enzyme carries out the first committed step in steroid hormone biosynthesis. StAR expression is restricted to steroidogenic cells and is rapidly induced by treatment with trophic hormones or cAMP. We analyzed the 5'-flanking region of the mouse StAR gene to elucidate the mechanisms that regulate its cell-specific and hormone-induced expression. In transient transfection assays, a luciferase reporter gene driven by the StAR 5'-flanking region was preferentially expressed by steroidogenic Y1 adrenocortical and MA-10 Leydig cells in a cAMP-responsive manner. 5'-Deletion and site-directed mutagenesis studies identified a region between -254 and -113 that is essential for full levels of promoter activity. This region contains a binding site for the orphan nuclear receptor steroidogenic factor-1 (SF-1) that, although not required for hormone induction, is critical for basal promoter activity, thus implicating SF-1 in StAR expression. Analyses of knockout mice deficient in SF-1 further supported an important role for SF-1 in StAR gene expression. These studies provide novel insights into the mechanisms that regulate StAR gene expression and extend our understanding of SF-1's global roles within steroidogenic cells.

Steroidogenic factor 1 plays multiple roles in endocrine development and function

The nuclear hormone receptor family comprises a group of structurally related transcriptional regulators that mediate the actions of diverse ligands, including steroid hormones, thyroid hormone, vitamin D, and retinoids. The nuclear receptor family also contains members for which activating ligands have not been identified-the orphan nuclear receptors. One of these orphan nuclear receptors, steroidogenic factor 1 (SF-1), has emerged as an essential regulator of steroidogenic cell function within the adrenal cortex and gonads; SF-1 also plays important roles in reproduction at all three levels of the hypothalamic-pituitary-gonadal axis. First identified as a tissue-specific regulator of the transcription of the cytochrome P450 steroid hydroxylases, considerably broader roles for SF-1 were revealed by genetic studies in mice lacking SF-1 due to targeted gene disruption. These SF-1-knockout mice had agenesis of their adrenal glands and gonads, male-to-female sex reversal of their internal and external genitalia, impaired gonadotrope function, and agenesis of the ventromedial hypothalamic nucleus. These studies delineated essential roles of SF-1 in regulating endocrine differentiation and function at multiple levels. Despite these insights into roles of SF-1, the precise mechanisms by which SF-1 exerts its multiple effects remain to be determined. This review highlights experiments that have established SF-1 as a pivotal determinant of endocrine differentiation and function and identifies areas in which additional studies are needed to expand our understanding of SF-1 action.

Steroidogenic factor 1 acts at all levels of the reproductive axis

The conversion of cholesterol into steroid hormones occurs through the sequential actions of the cytochrome P450 steroid hydroxylases. Attempts to understand the mechanisms responsible for the temporal and spatial expression patterns of these enzymes led to the identification of a shared regulator, termed steroidogenic factor 1 (SF-1). SF-1 coordinately regulates the steroid hydroxylase genes and thus functions as a global mediator of steroidogenesis. Of greater significance, recent studies using a knockout mouse model have further implicated SF-1 in a variety of processes ranging from development of the steroidogenic organs to the normal function of gonadotropes and the development of the ventromedial hypothalamic nucleus. A fundamental aspect of elucidating the role of SF-1 at all levels of the reproductive axis is to identify its cell-specific target genes. The recent purification and cloning of the steroidogenic acute regulatory (StAR) protein has provided an intriguing new candidate through which SF-1 acts to mediate its effects on reproductive competence. These studies yield novel insights into the processes of steroidogenesis, endocrine development, and reproductive function.

Differentiation of VEP intermodulation and second harmonic components by dichoptic, monocular, and binocular stimulation

Modulation by two temporal frequencies differentiates visual processing at the fundamentals (1Fs), second harmonics (2Fs), and second-order intermodulation components (IMCs), the latter created neurally as the sum or difference of the two modulation frequencies. Steady-state VEPs were recorded while stereo-normal adults viewed luminance or grating stimuli modulated by up to three temporal frequencies under dichoptic, monocular, or ordinary (binocular) viewing conditions arranged using liquid crystal light shutters. In Experiment 1, modulation of luminance by a single temporal frequency produced strong 1F and 2F VEP components, but modulation of gratings produced only 2Fs. Modulation by two temporal frequencies resulted in IMCs, often in the absence of evoked activity in the EEG at the 1Fs. IMCs were generally larger during pattern as compared to luminance modulation. Amplitudes of 1Fs and IMCs were smaller, but 2Fs were larger, during dichoptic as compared to ordinary viewing. Although the 2F to a single modulation presented to one eye was not reduced when a second frequency was added to the opposite eye, monocular IMCs were diminished when a frequency was added to the opposite eye. We conclude that 2Fs and IMCs are associated with different neural substrates. Results are consistent with a two pathway model with one pathway having a nonlinear filter prior to binocular combination, the other pathway having a nonlinearity following binocular linear summation. Implications of these data for binocular function are discussed.

Adrenocortical-specific transgene expression directed by steroid hydroxylase gene promoters

The 5'-flanking regions of genes for three mouse adrenal steroid hydroxylases were analyzed for their ability to direct adrenal cortex-specific beta-galactosidase (beta-gal) reporter expression both in cell culture and transgenic mice. The 5'-flanking regions chosen were from the genes for steroid 21-hydroxylase (21-OHase), expressed throughout the adrenal cortex and mediating both glucocorticoid and mineralocorticoid synthesis, and aldosterone synthetase (AS) and steroid 11 beta-hydroxylase (11 beta-OHase), which catalyze respectively the terminal steps of mineralocorticoid synthesis in the zona glomerulosa and glucocorticoid synthesis in the zona fasciculata/reticularis. While 5.0 kb of 11 beta-OHase gene 5'-flanking region and 5.4 kb of the AS gene 5'-flanking region mediated respectively moderate and low levels of beta-gal reporter expression in Y1 adrenocortical tumor cells, neither of these 5'-flanking regions was able to direct reporter expression to the appropriate adrenocortical zone of transgenic mice. This suggests that additional regulatory elements, lying outside these 5'-flanking regions, are required for 11 beta-OHase and AS gene expression in the intact mouse. In contrast, 6.4 kb of the mouse 21-OHase A gene 5' flanking region was able to direct specific beta-galactosidase reporter expression, in both Y1 cells and transgenic mice, indicating that elements directing adrenal cortex-specific gene expression in vivo are located not more than 6.4 kb 5' of the 21-OHase gene transcription start site.

Cloning and sequence analysis of the human gene encoding steroidogenic factor 1

The orphan nuclear receptor steroidogenic factor 1 (SF-1) plays key roles in endocrine development and function. Initially identified as a positive regulator of the cytochrome P450 steroid hydroxylases, analyses of knockout mice deficient in SF-1 revealed that SF-1 is essential for adrenal and gonadal development, pituitary gonadotropin expression and formation of the ventromedial hypothalamic nucleus. Although more limited in scope, analyses of SF-1 in humans similarly have suggested that SF-1 is important for differentiated function in adrenocortical and gonadotrope adenomas. In the hope of extending our understanding of SF-1 function by identifying possible roles of SF-1 in clinical endocrine disorders, we isolated the FTZ-F1 gene encoding human SF-1 and mapped it to chromosome 9q33. In this report, we characterize the sequence and structural organization of the human cDNA and gene encoding SF-1, providing new insights into comparative aspects of SF-1 structure that will facilitate efforts to study the role of this transcription factor in human endocrine disorders.

Steroidogenic factor 1 and Dax-1 colocalize in multiple cell lineages: potential links in endocrine development

Mutations of the orphan nuclear receptors, steroidogenic factor 1 (SF-1) and DAX-1, cause complex endocrine phenotypes that include impaired adrenal development and hypogonadotrophic hypogonadism. These similar phenotypes suggest that SF-1 and DAX-1 act in the same pathway(s) of endocrine development. To explore this model, we now compare directly their sites of expression. In mouse embryos, SF-1 expression in the urogenital ridge and brain either preceded or coincided with Dax-1 expression, with coordinate expression thereafter in the adrenal cortex, testis, ovary, hypothalamus, and anterior pituitary. The striking colocalization of SF-1 and Dax-1 supports the model that they are intimately linked in a common pathway of endocrine development. The slightly earlier onset of SF-1 expression and its ability to bind specifically to a conserved sequence in the Dax-1 5'-flanking region suggested that SF-1 may activate Dax-1 expression. However, promoter activity of Dax-1 5'-flanking sequences did not require this potential SF-1-responsive element, and Dax-1 expression was unimpaired in knockout mice lacking SF-1, establishing that SF-1 is not required for Dax-1 gene expression in these settings. Although the precise mechanisms remain to be established and may be multifactorial, our results strongly suggest that these two orphan nuclear receptors interact in a common pathway of endocrine development.

The roles of the nuclear receptor steroidogenic factor 1 in endocrine differentiation and development

The orphan nuclear receptor steroidogenic factor 1 (SF-1) has emerged as a critical determinant of adrenal and gonadal differentiation, development, and function. SF-1 was initially isolated as a positive regulator of the cytochrome P450 steroid hydroxylases in the adrenal glands and gonads; developmental analyses subsequently showed that SF-1 was also expressed in the diencephalon and anterior pituitary, suggesting additional roles in endocrine function. Analyses of knockout mice deficient in SF-1 revealed multiple abnormalities, including adrenal and gonadal agenesis, male to female sex reversal of the internal genitalia, impaired gonadotrope function, and absence of the ventromedial hypothalamic nucleus. Taken together, these results implicate SF-1 as a global regulator within the hypothalamic-pituitary-gonadal axis and the adrenal cortex.

The transcription activator steroidogenic factor-1 is preferentially expressed in the human pituitary gonadotroph

Steroidogenic factor-1 (SF-1), also known as adrenal-4-binding protein, is a transcription factor that is important for the differentiation of steroidogenic tissues. We investigated whether SF-1 is expressed in specific hormone-producing cell types in the human pituitary and its adenomas. Pituitary adenomas (n = 35) were collected at the time of surgery, and normal adenohypophyses were obtained from autopsies; 3 corticotroph adenomas were excluded because pit-1 messenger ribonucleic acid (mRNA) expression indicated contamination by nontumorous elements. Expression of SF-1 mRNA was determined by reverse transcription-PCR. SF-1 protein was localized with immunocytochemistry. By reverse transcription-PCR, SF-1 mRNA was found in the nontumorous pituitary and in pituitary adenomas expressing gonadotropins. All 8 gonadotroph adenomas had a strong signal for SF-1. SF-1 mRNA was also detected in 2 of 3 corticotroph adenomas, 2 of 13 somatotroph/mammosomatotroph adenomas, 1 of 6 lactotroph adenomas, and 2 silent subtype 3 adenomas; however, in most of the positive tumors there was also positivity for FSH beta and/or LH beta mRNA, suggesting that contaminating nontumorous gonadotrophs may be the source of SF-1 mRNA signal. SF-1 protein was localized by immunocytochemistry in the nuclei of scattered cells of the nontumorous adenohypophysis that were shown to be gonadotrophs with double immunostaining and in gonadotroph adenomas; nuclear staining was not found in other adenoma types, except in areas shown to contain trapped nontumorous tissue. We conclude that SF-1 expression correlates with the expression of gonadotropins. These findings implicate SF-1 as a cell-specific transcription factor that may regulate gonadotroph differentiation in the pituitary.

Expression of steroidogenic factor-1 (SF-1) mRNA and protein in the human placenta

Steroidogenic factor-1 (SF-1), also known as adrenal-4-binding protein (Ad4BP), is a recently-described transcription factor, which has been shown to be important for the differentiation of steroidogenic tissues. In addition, SF-1 has been implicated in regulating the glycoprotein hormone alpha-subunit gene in a pituitary gonadotroph cell line. Considering that the human placenta produces both steroids and human chorionic gonadotrophin (HCG), we studied the expression of SF-1 in this tissue. Human first trimester and term placentas were collected at the time of therapeutic abortion and birth respectively. Messenger RNA was extracted, reverse transcribed, and used for polymerase chain reaction (PCR) amplification with primers specific for the human SF-1 cDNA sequence. A band of the expected size was obtained from both first and third trimester samples, indicating that SF-1 expression in the human placenta starts early in pregnancy and is maintained until birth. In addition to normal placental samples, JEG3 and JAR choriocarcinoma cells were also analysed and found to express SF-1 mRNA. The identity of the amplified products was confirmed by diagnostic restriction digest and Southern hybridization. SF-1 protein was localized mainly to the nuclei of the cyto- and syncytiotrophoblast and to some mesenchymal villous nuclei by immunocytochemistry using a specific antibody. We conclude that SF-1 is expressed in human first trimester and term placenta, where it could be implicated in the regulation of HCG production, in steroidogenesis, or both.

Variegated expression of a mouse steroid 21-hydroxylase/beta- galactosidase transgene suggests centripetal migration of adrenocortical cells

5'-Flanking sequences (6.4 kb) of the mouse steroid 21-hyrodxylase (21-OHase) A gene linked to a LacZ reporter gene directed appropriate cell-specific expression in cultured Y1 adrenocortical tumor cells and in the adrenal cortex of transgenic mice. The transgene expression initiated at the same stage of adrenal development as the endogenous 21-OHase gene (embryonic day 11.5). Although the endogenous 21-OHase gene is expressed throughout the adrenal cortex, the 21-OHase/beta-gal transgene showed a strikingly variegated pattern of adrenocortical expression in all 10 transgene-expressing mouse lines examined. This presents as radial stripes of beta-gal staining transcending the classical zonal structure of the adrenal cortex but paralleling the columnar arrangement of cells of the zona fasciculata on the centripetal organization of the adrenocortical blood supply. To the extent that the variegated pattern of 21-OHase/beta-gal transgene expression depicts adrenocortical cell lineage, these results suggest that all cells within an individual stripe have a common clonal origin; the radial pattern of clonally derived cells argues that cellular migration maintains the adult adrenocortical cell population. Adrenal glands of developing embryos also exhibited a variegated pattern of 21-OHase/beta-gal transgene expression. However, this presented as islands of beta-gal reporter staining within the developing gland, suggesting that the rapid embryonic adrenal growth phase, which precedes the establishment of the classic adrenocortical zonal structure, may be governed by cellular mechanisms distinct from those responsible for maintenance of the adult adrenocortical cell population.

The roles of steroidogenic factor-1 in reproductive function

The cytochrome P450 steroid hydroxylases are expressed in a tissue-specific and developmentally regulated manner, and the orphan nuclear receptor steroidogenic factor 1 (SF-1) participates in both aspects of regulated expression. SF-1 is expressed in mouse embryos from the inception of adrenal and gonadal development, suggesting that SF-1 plays important roles in their differentiation. SF-1 is also expressed in the embryonic pituitary gland and ventral diencephalon, suggesting additional roles within the hypothalamic-pituitary-steroidogenic organ axis. To examine the roles of SF-1 in vivo, we used targeted gene disruption to "knock out" the mouse gene encoding SF-1. Analyses of these knockout mice established roles of SF-1 at levels of endocrine development that include adrenal and gonadal differentiation, pituitary gonadotrope function, and formation of the ventromedial hypothalamic nucleus. These results indicate that SF-1 plays multiple roles in endocrine development that are essential for reproduction.

The cell-specific nuclear receptor steroidogenic factor 1 plays multiple roles in reproductive function

The cytochrome P450 steroid hydroxylases exhibit tissue-specific and developmentally regulated gene expression. Recent studies showed that the orphan nuclear receptor steroidogenic factor 1 (SF-1) plays a key role in their gene regulation. In mouse embryos, SF-1 expression began at the inception of adrenal and gonadal development, suggesting that SF-1 plays a key role in the steroidogenic cell differentiation. SF-1 was also expressed in the developing pituitary gland and diencephalon, which raised the possibility that it also has additional roles in endocrine development. To examine the role of SF-1 in intact mice, we disrupted the gene encoding SF-1 by homologous recombination in embryonic stem cells; this approach ultimately permitted us to generate SF-1 knockout mice in which the gene encoding SF-1 was inactivated. These studies revealed essential roles of SF-1 in endocrine development that included adrenal and gonadal development, expression of several markers of pituitary gonadotropes, and formation of the ventromedial hypothalamic (VMH) nucleus. These results indicate that SF-1 acts at multiple levels of the reproductive axis to maintain reproductive competence.