[Show abstract][Hide abstract] ABSTRACT: 17 R esistance to thyroid hormone (RTH) was first de-scribed in 1967 (1), and the first mutations in the THRB gene were identified in 1989 (2,3), only three years after the cloning of the THR genes (4,5). The cardinal features of this syndrome of reduced sensitivity to thyroid hormone are el-evated serum levels of free thyroid hormone with non-suppressed thyrotropin (TSH), often with goiter and no clear symptoms and signs of thyrotoxicosis (6). In fact, signs of decreased and increased thyroid hormone action in different tissues may coexist. During the First International Workshop on Resistance to Thyroid Hormone in Cambridge, United Kingdom, in 1993, a consensus statement was issued to establish a unified no-menclature of THRB gene mutations in RTH (7), as defined above. In the ensuing years more than 3000 cases have been identified, 80% of which harbored mutations in the THRB gene. More recently, two syndromes with reduced cellular access of the biologically active thyroid hormone, triiodo-thyronine (T 3), were identified. These are caused by defects of thyroid hormone cell membrane transport (8,9) and a de-fect reducing the intracellular metabolism generating T 3 from thyroxine (T 4) (10). To accommodate these new findings, it was proposed to broaden the definition of hormone resis-tance. Thus, the Fifth International Workshop on Resistance to Thyroid Hormone, which took place in Lyon, France, in 2005, saw the introduction of the term ''reduced sensitivity to thyroid hormone (RSTH) to encompass all defects that can interfere with the biological activity of a chemically intact thyroid hormone secreted in normal or excessive amounts.'' Following the 10th International Workshop on Resistance to Thyroid Hormone and Action that took place in Quebec City, Canada, in 2012, a number of investigators took on the task to develop a nomenclature for inherited forms of im-paired sensitivity to thyroid hormone (Table 1). The term ''impaired'' was to substitute for ''reduced'' because nascent data indicate that syndromes of increased sensitivity may also exist. We are cognizant that no nomenclature can fit perfectly all aspects of the described syndromes because variability exists. Several aspects were taken into consideration: the already existing nomenclature, new findings, and anticipated putative discoveries. For example, in over 2000 publications ''RTH'' is used to define a phenotype of congenitally in-creased free T 4 with nonsuppressed TSH, irrespective of the presence or absence of a THRB gene mutation (see non-TR-RTH). In view of the identification of THRA gene mu-tations that present a distinct phenotype (11,12), we propose using the term ''RTH a,'' and in new publications to use ''RTH b'' when a THRB gene mutation is present in Citation of this publication should include the three journals in which it has been simultaneously published: Journal of Clinical Endocrinology and Metabolism, Thyroid, and European Thyroid Journal. Departments of
[Show abstract][Hide abstract] ABSTRACT: Genome-wide mutagenesis was performed in mice to identify candidate genes for male infertility, for which the predominant causes remain idiopathic. Mice were mutagenized using N-ethyl-N-nitrosourea (ENU), bred, and screened for phenotypes associated with the male urogenital system. Fifteen heritable lines were isolated and chromosomal loci were assigned using low-density genome-wide SNP arrays. Ten of the 15 lines were pursued further using higher-resolution SNP analysis to narrow the candidate gene regions. Exon sequencing of candidate genes identified mutations in mice with cystic kidneys (Bicc1), cryptorchidism (Rxfp2), restricted germ cell deficiency (Plk4), and severe germ cell deficiency (Prdm9). In two other lines with severe hypogonadism, candidate sequencing failed to identify mutations, suggesting defects in genes with previously undocumented roles in gonadal function. These genomic intervals were sequenced in their entirety and a candidate mutation was identified in SnrpE in one of the two lines. The line harboring the SnrpE variant retains substantial spermatogenesis despite small testis size, an unusual phenotype. In addition to the reproductive defects, heritable phenotypes were observed in mice with ataxia (Myo5a), tremors (Pmp22), growth retardation (unknown gene), and hydrocephalus (unknown gene). These results demonstrate that the ENU screen is an effective tool for identifying potential causes of male infertility.
[Show abstract][Hide abstract] ABSTRACT: The genetic etiologies of male infertility remain largely unknown. To identify genes potentially involved in spermatogenesis and male infertility, we performed genome-wide mutagenesis in mice with N-ethyl-N-nitrosourea and identified a line with dominant hypogonadism and patchy germ cell loss. Genomic mapping and DNA sequence analysis identified a novel heterozygous missense mutation in the kinase domain of Polo-like kinase 4 (Plk4), altering an isoleucine to asparagine at residue 242 (I242N). Genetic complementation studies using a gene trap line with disruption in the Plk4 locus confirmed that the putative Plk4 missense mutation was causative. Plk4 is known to be involved in centriole formation and cell cycle progression. However, a specific role in mammalian spermatogenesis has not been examined. PLK4 was highly expressed in the testes both pre- and postnatally. In the adult, PLK4 expression was first detected in stage VIII pachytene spermatocytes and was present through step 16 elongated spermatids. Because the homozygous Plk4(I242N/I242N) mutation was embryonic lethal, all analyses were performed using the heterozygous Plk4(+/I242N) mice. Testis size was reduced by 17%, and histology revealed discrete regions of germ cell loss, leaving only Sertoli cells in these defective tubules. Testis cord formation (embryonic day 13.5) was normal. Testis histology was also normal at postnatal day (P)1, but germ cell loss was detected at P10 and subsequent ages. We conclude that the I242N heterozygous mutation in PLK4 is causative for patchy germ cell loss beginning at P10, suggesting a role for PLK4 during the initiation of spermatogenesis.
[Show abstract][Hide abstract] ABSTRACT: Steroidogenic factor 1 (SF-1) is essential for the development and function of steroidogenic tissues. Stable incorporation of SF-1 into embryonic stem cells (SF-1-ES cells) has been shown to prime the cells for steroidogenesis. When provided with exogenous cholesterol substrate, and after treatment with retinoic acid and cAMP, SF-1-ES cells produce progesterone but do not produce other steroids such as cortisol, estradiol, or testosterone. In this study, we explored culture conditions that optimize SF-1-mediated differentiation of ES cells into defined steroidogenic lineages. When embryoid body formation was used to facilitate cell lineage differentiation, SF-1-ES cells were found to be restricted in their differentiation, with fewer cells entering neuronal pathways and a larger fraction entering the steroidogenic lineage. Among the differentiation protocols tested, leukemia inhibitory factor (LIF) removal, followed by prolonged cAMP treatment was most efficacious for inducing steroidogenesis in SF-1-ES cells. In this protocol, a subset of SF-1-ES cells survives after LIF withdrawal, undergoes morphologic differentiation, and recovers proliferative capacity. These cells are characterized by induction of steroidogenic enzyme genes, use of de novo cholesterol, and production of multiple steroids including estradiol and testosterone. Microarray studies identified additional pathways associated with SF-1 mediated differentiation. Using biotinylated SF-1 in chromatin immunoprecipitation assays, SF-1 was shown to bind directly to multiple target genes, with induction of binding to some targets after steroidogenic treatment. These studies indicate that SF-1 expression, followed by LIF removal and treatment with cAMP drives ES cells into a steroidogenic pathway characteristic of gonadal steroid-producing cells.
[Show abstract][Hide abstract] ABSTRACT: DAX1 (dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1; also known as NROB1, nuclear receptor subfamily 0, group B, member 1) encodes a nuclear receptor that is expressed in embryonic stem (ES) cells, steroidogenic tissues (gonads, adrenals), the ventromedial hypothalamus (VMH), and pituitary gonadotropes. Humans with DAX1 mutations develop an X-linked syndrome referred to as adrenal hypoplasia congenita (AHC). These boys typically present in infancy with adrenal failure but later fail to undergo puberty because of hypogonadotropic hypogonadism (HHG). The adrenal failure reflects a developmental abnormality in the transition of the fetal to adult zone, resulting in glucocorticoid and mineralocorticoid deficiency. The etiology of HHG involves a combined and variable deficiency of hypothalamic GnRH secretion and/or pituitary responsiveness to GnRH resulting in low LH, FSH and testosterone. Treatment with exogenous gonadotropins generally does not induce spermatogenesis. Animal models indicate that DAX1 also plays a critical role in testis development and function. As a nuclear receptor, DAX1 has been shown to function as a transcriptional repressor, particularly of pathways regulated by other nuclear receptors, such as steroidogenic factor 1 (SF1). In addition to reproductive tissues, DAX1 is also expressed at high levels in ES cells and plays a role in the maintenance of pluripotentiality. Here we review the clinical manifestations associated with DAX1 mutations as well as the evolving information about its function based on animal models and in vitro studies.
Molecular and Cellular Endocrinology 06/2011; 346(1-2):65-73. · 4.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The X-linked Sox3 gene encodes a member of the Sry high-mobility group box proteins, which play a role in many developmental processes including neurogenesis and testis development. This study further examined the role of Sox3 in spermatogenesis. Males without Sox3 expression exhibited a similar number of germ cell nuclear antigen-positive germ cells at 1, 5, and 10 d postpartum (dpp) compared to their wild-type littermates, but there was significant germ cell depletion by 20 dpp. However, spermatogenesis later resumed and postmeiotic germ cells were observed by 56 dpp. The VasaCre transgene was used to generate a germ cell-specific deletion of Sox3. The phenotype of the germ cell-specific Sox3 knockout was similar to the ubiquitous knockout, indicating an intrinsic role for Sox3 in germ cells. The residual germ cells in 20 dpp Sox3(-/Y) males were spermatogonia as indicated by their expression of neurogenin3 but not synaptonemal complex protein 3, which is expressed within cells undergoing meiosis. RNA expression analyses corroborated the histological analyses and revealed a gradual transition from relatively increased expression of spermatogonia genes at 20 dpp to near normal expression of genes characteristic of undifferentiated and meiotic germ cells by 84 dpp. Fluorescent-activated cell sorting of undifferentiated (ret tyrosine kinase receptor positive) and differentiated (kit receptor tyrosine kinase-positive) spermatogonia revealed depletion of differentiated spermatogonia in Sox3(-/Y) tubules. These results indicate that Sox3 functions in an intrinsic manner to promote differentiation of spermatogonia in prepubertal mice but it is not required for ongoing spermatogenesis in adults. The Sox3(-/Y) males provide a unique model for studying the mechanism of germ cell differentiation in prepubertal testes.
[Show abstract][Hide abstract] ABSTRACT: In addition to its role in reproduction, estradiol-17β is critical to the regulation of energy balance and body weight. Estrogen receptor α-null (Erα-/-) mutant mice develop an obese state characterized by decreased energy expenditure, decreased locomotion, increased adiposity, altered glucose homeostasis, and hyperleptinemia. Such features are reminiscent of the propensity of postmenopausal women to develop obesity and type 2 diabetes. The mechanisms by which ERα signaling maintains normal energy balance, however, have remained unclear. Here we used knockin mice that express mutant ERα that can only signal through the noncanonical pathway to assess the role of nonclassical ERα signaling in energy homeostasis. In these mice, we found that nonclassical ERα signaling restored metabolic parameters dysregulated in Erα-/- mutant mice to normal or near-normal values. The rescue of body weight and metabolic function by nonclassical ERα signaling was mediated by normalization of energy expenditure, including voluntary locomotor activity. These findings indicate that nonclassical ERα signaling mediates major effects of estradiol-17β on energy balance, raising the possibility that selective ERα agonists may be developed to reduce the risks of obesity and metabolic disturbances in postmenopausal women.
The Journal of clinical investigation 02/2011; 121(2):604-12. · 15.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Using genome-wide mutagenesis with N-ethyl-N-nitrosourea (ENU), a mouse mutant with cryptorchidism was identified. Genome mapping and exon sequencing identified a novel missense mutation (D294G) in Relaxin/insulin-like family peptide receptor 2 (Rxfp2). The mutation impaired testicular descent and resulted in decreased testis weight in Rxfp2 ( DG/DG ) mice compared to Rxfp2 (+/DG ) and Rxfp2 (+/+) mice. Testicular histology of the Rxfp2 ( DG/DG ) mice revealed spermatogenic defects ranging from germ cell loss to tubules with Sertoli-cell-only features. Genetic complementation analysis using a loss-of-function allele (Rxfp2 (-)) confirmed causality of the D294G mutation. Specifically, mice with one of each mutant allele (Rxfp2 ( DG/-)) exhibited decreased testis weight and failure of the testes to descend compared to their Rxfp2 (+/-) littermates. Total and cell-surface expression of mouse RXFP2 protein and intracellular cAMP accumulation were measured. Total expression of the D294G protein was minimally reduced compared to wild-type, but cell-surface expression was markedly decreased. When analyzed for cAMP accumulation, the EC50 was similar for cells transfected with wild-type and mutant RXFP2 receptor. However, the maximum cAMP response that the mutant receptor reached was greatly reduced compared to the wild-type receptor. In silico modeling of leucine rich repeats (LRRs) 7-9 indicated that aspartic acid 294 is located within the β-pleated sheet of LRR8. We thus postulate that mutation of D294 results in protein misfolding and aberrant trafficking. The ENU-induced D294G mutation underscores the role of the INSL3/RXFP2-mediated pathway in testicular descent and expands the repertoire of mutations known to affect receptor trafficking and function.
[Show abstract][Hide abstract] ABSTRACT: The study objective was to determine whether stromal and/or epithelial estrogen receptor-alpha (ERalpha) is required for relaxin to promote proliferation of stromal and epithelial cells in the mouse cervix. Four types of tissue recombinants were prepared with cervical stroma (St) and epithelium (Ep) from wild-type (wt) and ERalpha knockout (ko) mice: wt-St+wt-Ep, wt-St+ko-Ep, ko-St+wt-Ep and ko-St+ko-Ep. Tissue recombinants were grafted under the renal capsule of syngeneic female mice. After 3 wk of transplant growth, hosts were ovariectomized and fitted with silicon implants containing 17beta-estradiol (treatment d 1). Animals were injected sc with relaxin or vehicle PBS at 6-h intervals from 0600 h on d 8 through 0600 h on d 10. To evaluate cell proliferation, 5-bromo-2'-deoxyuridine was injected sc 10 h before tissue recombinants were collected at 1000 h on d 10. Relaxin promoted marked proliferation of both epithelial and stromal cells in tissue recombinants containing wt St (P < 0.001) but far lower proliferation in recombinants prepared with ko St, regardless of whether Ep was derived from wt or ko mice. An additional experiment using mice expressing wt ERalpha, a mutant of ERalpha that selectively lacks classical signaling through estrogen response element binding, or no ERalpha demonstrated that ERalpha must bind to an estrogen response element to enable relaxin's proliferative effects. In conclusion, this study shows that ERalpha-expressing cells in St, using a classical signaling pathway, are necessary for relaxin to promote marked proliferation in both stromal and epithelial cells of the mouse cervix.
[Show abstract][Hide abstract] ABSTRACT: In vitro models have been used to demonstrate that estrogen receptors (ERs) can regulate estrogen-responsive genes either by directly interacting with estrogen-responsive element (ERE) DNA motifs or by interacting with other transcription factors such as AP1. In this study, we evaluated estrogen (E(2))-dependent uterine gene profiles by microarray in the KIKO mouse, an in vivo knock-in mouse model that lacks the DNA-binding function of ERalpha and is consequently restricted to non-ERE-mediated responses. The 2- or 24-h E(2)-mediated uterine gene responses were distinct in wild-type (WT), KIKO, and alphaERKO genotypes, indicating that unique sets of genes are regulated by ERE and non-ERE pathways. After 2 h E(2) treatment, 38% of the WT transcripts were also regulated in the KIKO, demonstrating that the tethered mechanism does operate in this in vivo model. Surprisingly, 1438 E(2)-regulated transcripts were unique in the KIKO mouse and were not seen in either WT or alphaERKO. Pathway analyses revealed that some canonical pathways, such as the Jak/Stat pathway, were affected in a similar manner by E(2) in WT and KIKO. In other cases, however, the WT and KIKO differed. One example is the Wnt/beta-catenin pathway; this pathway was impacted, but different members of the pathway were regulated by E(2) or were regulated in a different manner, consistent with differences in biological responses. In summary, this study provides a comprehensive analysis of uterine genes regulated by E(2) via ERE and non-ERE pathways.
[Show abstract][Hide abstract] ABSTRACT: Foxl2 is a forkhead transcription factor required for ovary development and ovarian follicle maturation. In this report, we identified and characterized a functional relationship between Foxl2 expression and estrogen receptor (ER)-alpha signaling. We show that Foxl2 has no effect on classical ERalpha-mediated transcription, which occurs through canonical estrogen response elements. However, Foxl2 suppresses ERalpha signaling through nonclassical tethered transcriptional pathways. Specifically, the selective ER modulator tamoxifen stimulates activator protein-1 (AP1)-dependent transcription via the ERalpha, and this enhancement is blocked by Foxl2. Two lines of evidence suggest that Foxl2 suppression is mediated by physical interactions with ERalpha rather than direct action at AP1 binding sites. First, ERalpha is coimmunoprecipitated with Foxl2. Second, activation of a upstream activating sequence (UAS) reporter by Gal4-cJun in the presence of ERalpha and tamoxifen was blocked by Foxl2, demonstrating suppression in the absence of an AP1 site. Cyclooxygenase-2 (COX2), which is required for ovulation, was identified through expression profiling as a candidate physiological target for nonclassical ERalpha signaling and thus modulation by ERalpha/Foxl2 interactions. This possibility was confirmed by two sets of experiments. COX2 protein levels were induced by ERalpha in the presence of tamoxifen, and protein expression was suppressed by Foxl2. In addition, ERalpha stimulation of the COX2 promoter was repressed by Foxl2. We conclude that ERalpha and Foxl2 interact and that Foxl2 selectively suppresses ERalpha-mediated transcription of AP1-regulated genes. These data provide a potential point of convergence for ERalpha and Foxl2 to regulate ovarian development and function.
[Show abstract][Hide abstract] ABSTRACT: Aromatase (CYP19A1) catalyzes the conversion of C(19) steroids to estrogens. Aromatase and its product estradiol (E(2)) are crucial for the sexually dimorphic development of the fetal brain and the regulation of gonadotropin secretion and sexual interest in adults. The regulation of aromatase expression in the brain is not well understood. The aromatase (Cyp19a1) gene is selectively expressed in distinct neurons of the hypothalamus through a distal brain-specific promoter I.f located approximately 36 kb upstream of the coding region. Here, we investigated a short feedback effect of E(2) on aromatase mRNA expression and enzyme activity using estrogen receptor alpha (ESR1; also known as ER alpha)-positive or ESR1-negative mouse embryonic hypothalamic neuronal cell lines that express aromatase via promoter I.f. Estradiol regulated aromatase mRNA expression and enzyme activity in a time- and dose-dependent manner, whereas an E(2) antagonist reversed these effects. The nucleotide -200/-1 region of promoter I.f conferred E(2) responsiveness. Two activator protein 1 (AP-1) elements in this region were essential for induction of promoter activity by E(2). ESR1 and JUN (c-Jun) bound to these AP-1 motifs in intact cells and under cell-free conditions. The addition of an ESR1 mutant that interacts with JUN but not directly with DNA enhanced E(2)-dependent promoter I.f activity. Independently, we demonstrated an interaction between ESR1 and JUN in hypothalamic cells. Knockdown of ESR1 abolished E(2)-induced aromatase mRNA and enzyme activity. Taken together, E(2) regulates Cyp19a1 expression via promoter I.f by enhanced binding of an ESR1/JUN complex to distinct AP-1 motifs in hypothalamic cells. We speculate that this mechanism may, in part, regulate gonadotropin secretion and sexual activity.
Biology of Reproduction 08/2009; 81(5):956-65. · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Kisspeptin is a product of the Kiss1 gene and is expressed in the forebrain. Neurons that express Kiss1 play a crucial role in the regulation of pituitary luteinizing hormone secretion and reproduction. These neurons are the direct targets for the action of estradiol-17beta (E(2)), which acts via the estrogen receptor alpha isoform (ER alpha) to regulate Kiss1 expression. In the arcuate nucleus (Arc), where the dynorphin gene (Dyn) is expressed in Kiss1 neurons, E(2) inhibits the expression of Kiss1 mRNA. However, E(2) induces the expression of Kiss1 in the anteroventral periventricular nucleus (AVPV). The mechanism for differential regulation of Kiss1 in the Arc and AVPV by E(2) is unknown. ER alpha signals through multiple pathways, which can be categorized as either classical, involving the estrogen response element (ERE), or nonclassical, involving ERE-independent mechanisms. To elucidate the molecular basis for the action of E(2) on Kiss1 and Dyn expression, we studied the effects of E(2) on Kiss1 and Dyn mRNAs in the brains of mice bearing targeted alterations in the ER alpha signaling pathways. We found that stimulation of Kiss1 expression by E(2) in the AVPV and inhibition of Dyn in the Arc required an ERE-dependent pathway, whereas the inhibition of Kiss1 expression by E(2) in the Arc involved ERE-independent mechanisms. Thus, distinct ER alpha signaling pathways can differentially regulate the expression of identical genes across different brain regions, and E(2) can act within the same neuron through divergent ER alpha signaling pathways to regulate different neurotransmitter genes.
Journal of Neuroscience 08/2009; 29(29):9390-5. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mutations of the gsp oncogene are responsible for 30-40% of GH-producing pituitary adenomas and 10% of nonfunctioning pituitary adenomas (NFPAs). However, the pathogenetic mechanism of the remaining pituitary tumours still remains to be identified. Recently, the interaction between the chemokine stromal cell-derived factor 1 and its receptor CXCR4 was found to play an important role in GH production and cell proliferation in various pituitary adenoma cell lines. As CXCR4 is a Gi-coupled chemokine receptor, its constitutive activating mutations may be involved in pituitary tumour formation by cyclic adenosine monophosphate (cAMP)-independent, ERK-related pathways.
We investigated whether somatic activating-mutations of CXCR4 might be a possible tumourigenic mechanism for gsp-negative GH-secreting pituitary adenomas and NFPAs. Direct sequencing of polymerase chain reaction-amplified products for coding exons of CXCR4 were performed using genomic deoxyribonucleic acid samples from 37 GH-producing pituitary tumour tissues that were negative for the gsp mutation and 14 CXCR4 expressing NFPAs.
Immunohistochemical analyses and double immunofluorescent staining of sectioned paraffin-embedded pituitary tissues revealed that CXCR4 is highly expressed in GH-producing pituitary adenomas and NFPAs. Direct sequencing showed that two synonymous mutations in exon 2 (87 C > T and 414 C > T) were detected in 4 out of 51 pituitary tumours.
Our results indicate that an activating mutation of the CXCR4 may not be a common pathogenetic mechanism in GH-producing pituitary tumours and NFPAs.
[Show abstract][Hide abstract] ABSTRACT: Nonclassical estrogen receptor alpha (ERalpha) signaling can mediate E(2) negative feedback actions in the reproductive axis; however, downstream pathways conveying these effects remain unclear. These studies tested the hypothesis that p21-activated kinase 1 (PAK1), a serine/threonine kinase rapidly activated by E(2) in nonneural cells, functions as a downstream node for E(2) signaling pathways in cells of the preoptic area, and it may thereby mediate E(2) negative feedback effects. Treatment of ovariectomized (OVX) rats with estradiol benzoate (EB) caused rapid and transient induction of phosphorylated PAK1 immunoreactivity in the medial preoptic nucleus (MPN) but not the arcuate nucleus. To determine whether rapid induction of PAK phosphorylation by E(2) is mediated by nonclassical [estrogen response element (ERE)-independent] ERalpha signaling, we used female ERalpha null (ERalpha(-/-)) mice possessing an ER knock-in mutation (E207A/G208A; AA), in which the mutant ERalpha is incapable of binding DNA and can signal only through membrane-initiated or ERE-independent genotropic pathways (ERalpha(-/AA) mice). After 1-h EB treatment, the number of pPAK1-immunoreactive cells in the MPN was increased in both wild-type (ERalpha(+/+)) and ERalpha(-/AA) mice but was unchanged in ERalpha(-/-) mice. Serum luteinizing hormone (LH) was likewise suppressed within 1 h after EB treatment in ERalpha(+/+) and ERalpha(-/AA) but not ERalpha(-/ -) mice. In OVX rats, 5-min intracerebroventricular infusion of a PAK inhibitor peptide but not control peptide blocked rapid EB suppression of LH secretion. Taken together, our findings implicate PAK1 activation subsequent to nonclassical ERalpha signaling as an important component of the negative feedback actions of E(2) in the brain.
Proceedings of the National Academy of Sciences 05/2009; 106(17):7221-6. · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nuclear receptor subfamily 0, group B, member 1 (Nr0b1; hereafter referred to as Dax1) is an orphan nuclear receptor that regulates adrenal and gonadal development. Dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 (Dax1) mutations in the mouse are sensitive to genetic background. In this report, a spectrum of impaired gonadal differentiation was observed as a result of crossing the Dax1 knockout on the 129SvIm/J strain onto the C57BL/6J strain over two generations of breeding. Dax1-mutant XY mice of a mixed genetic background (129;B6Dax1(-/Y) [101 total]) developed gonads that were predominantly testislike (n = 61), ovarianlike (n = 27), or as intersex (n = 13). During embryonic development, Sox9 expression in the gonads of 129;B6Dax1(-/Y) mutants was distributed across a wide quantitative range, and a threshold level of Sox9 (>0.4-fold of wild-type) was associated with testis development. Germ cell fate also varied widely, with meiotic germ cells being more prevalent in the ovarianlike regions of embryonic gonads, but also observed within testicular tissue. Ptgds, a gene associated with Sox9 expression and Sertoli cell development, was markedly downregulated in Dax1(-/Y) mice. Stra8, a gene associated with germ cell meiosis, was upregulated in Dax1(-/Y) mice. In both cases, the changes in gene expression also occurred in pure 129 mice but were amplified in the B6 genetic background. Sertoli cell apoptosis was prevalent in 129;B6Dax1(-/Y) gonads. In summary, Dax1 deficiency on a partial B6 genetic background results in further modulation of gene expression changes that affect both Sertoli cell and germ cell fate, leading to a phenotypic spectrum of gonadal differentiation.
Biology of Reproduction 12/2008; 79(6):1038-45. · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During the female reproductive cycle, the neuroendocrine action of estradiol switches from negative feedback to positive feedback to initiate the preovulatory GnRH and subsequent LH surges. Estrogen receptor-alpha (ERalpha) is required for both estradiol negative and positive feedback regulation of LH. ERalpha may signal through estrogen response elements (EREs) in DNA and/or via ERE-independent pathways. Previously, a knock-in mutant allele (ERalpha-/AA) that selectively restores ERE-independent signaling onto the ERalpha-/- background was shown to confer partial negative but not positive estradiol feedback on serum LH. The current study investigated the roles of the ERE-dependent and ERE-independent ERalpha pathways for estradiol feedback at the level of GnRH neuron firing activity. The above ERalpha genetic models were crossed with GnRH-green fluorescent protein mice to enable identification of GnRH neurons in brain slices. Targeted extracellular recordings were used to monitor GnRH neuron firing activity using an ovariectomized, estradiol-treated mouse model that exhibits diurnal switches between negative and positive feedback. In wild-type mice, GnRH neuron firing decreased in response to estradiol during negative feedback and increased during positive feedback. In contrast, both positive and negative responses to estradiol were absent in GnRH neurons from ERalpha-/- and ERalpha-/AA mice. ERE-dependent signaling is thus required to increase GnRH neuron firing to generate a GnRH/LH surge. Furthermore, ERE-dependent and -independent ERalpha signaling pathways both appear necessary to mediate estradiol negative feedback on serum LH levels, suggesting central and pituitary estradiol feedback may use different combinations of ERalpha signaling pathways.
[Show abstract][Hide abstract] ABSTRACT: The estrogen receptor-alpha (ERalpha) acts through multiple pathways, including estrogen response element (ERE)-dependent (classical) and ERE-independent (nonclassical) mechanisms. We previously created a mouse model harboring a two-amino-acid mutation of the DNA-binding domain (E207A, G208A) that precludes direct binding of ERalpha to an ERE. After crossing heterozygous mutant mice with an ERalpha knockout (ERKO) line, it was possible to assess the degree of physiological rescue by the isolated ERalpha nonclassical allele (-/AA; AA) when compared with ERKO mice (-/-) and to wild type (+/+; WT). In male ERKO mice up to 8 months of age, testosterone levels were high, although LH levels were similar to WT. Testosterone was normal in the AA mice, indicating that the AA allele rescues the enhanced testosterone biosynthesis in ERKO mice. Male ERKO mice exhibited distention of the seminiferous tubules as early as 2-3 months of age as a consequence of decreased water resorption in the efferent ducts. By 3-4 months of age, ERKO mice had impaired spermatogenesis in approximately 40% of their tubules, and sperm counts and motility declined in association with the histological changes. In the AA mice, histological defects were greatly reduced or absent, and sperm counts and motility were rescued. Levels of aquaporins 1 and 9, which contribute to water uptake in the efferent ducts, were reduced in ERKO mice and partially or fully rescued in AA mice, whereas another water transporter, sodium-hydrogen exchanger-3, was decreased in both ERKO and AA mice. We conclude that non-ERE-dependent estrogen pathways are sufficient to rescue the defective spermatogenesis observed in ERKO mice and play a prominent role in ERalpha action in the testis, including pathways that regulate water resorption and androgen biosynthesis.