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Joshua J Meeks

Publications and source records attributed to Joshua J Meeks.

8 recordsLinked to original sources
PubMed2005

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

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

Animals↗
PubMed2003

Leydig cell-specific expression of DAX1 improves fertility of the Dax1-deficient mouse.

Dax1 is an orphan nuclear receptor expressed in both Leydig and Sertoli cells of the testis. Mutation of DAX1 in humans causes adrenal failure and hypogonadotropic hypogonadism. Targeted mutagenesis of Dax1 in mice reveals a primary gonadal defect characterized by overexpression of aromatase and cellular obstruction of the seminiferous tubules and efferent ductules, leading to germ cell death and infertility. Transgenic expression of DAX1 under the control of the müllerian-inhibiting substance promoter, which is selectively expressed in Sertoli cells, improves fertility but does not fully correct the histological abnormalities in the testes of Dax1 knockout (Dax1KO) mice. We therefore hypothesized that Dax1 may also play a crucial role in other somatic cells of the testis, namely the Leydig cells. A 2.1-kilobase fragment of the murine LH receptor 5'-promoter (LHR-DAX1) was used to generate transgenic mice that selectively express DAX1 in Leydig cells. Expression of the LHR-DAX1 transgene caused no observable phenotype in wild-type mice but improved fertility when expressed in Dax1KO males (rescue [RS]). Although testicular size was not increased in LHR-DAX1 RS animals, aromatase expression was restored to normal levels, and sperm production was increased. Testicular pathology was only slightly improved in RS mice compared to Dax1KO animals. Taken together with the result of previous studies of DAX1 expression in Sertoli cells, we conclude that the testis phenotype of Dax1KO mice reflects the combined effects of Dax1 deficiency in both Sertoli and Leydig cells.

Animals↗
PubMed2003

Dax1 is required for testis determination.

The orphan nuclear receptor, Dax1, was originally proposed to act as an 'anti-testis' factor. We find, however, that Nr0b1 (also called Dax1 and Ahch, which encodes Dax1) is in fact required for testis differentiation.

Animals↗
PubMed2003

Sox3 is required for gonadal function, but not sex determination, in males and females.

Sox3 is expressed in developing gonads and in the brain. Evolutionary evidence suggests that the X-chromosomal Sox3 gene may be the ancestral precursor of Sry, a sex-determining gene, and Sox3 has been proposed to play a role in sex determination. However, patients with mutations in SOX3 exhibit normal gonadal determination but are mentally retarded and have short stature secondary to growth hormone (GH) deficiency. We used Cre-LoxP targeted mutagenesis to delete Sox3 from mice. Null mice of both sexes had no overt behavioral deficits and exhibited normal GH gene expression. Low body weight was observed for some mice; overgrowth and misalignment of the front teeth was observed consistently. Female Sox3 null mice (-/-) developed ovaries but had excess follicular atresia, ovulation of defective oocytes, and severely reduced fertility. Pituitary (luteinizing hormone and follicle-stimulating hormone) and uterine functions were normal in females. Hemizygous male null mice (-/Y) developed testes but were hypogonadal. Testis weight was reduced by 42%, and there was extensive Sertoli cell vacuolization, loss of germ cells, reduced sperm counts, and disruption of the seminiferous tubules. We conclude that Sox3 is not required for gonadal determination but is important for normal oocyte development and male testis differentiation and gametogenesis.

Animals↗
PubMed2003

SF1 in the development of the adrenal gland and gonads.

SF1 (steroidogenic factor-1; NR5A1) is an orphan nuclear receptor that is expressed in the adrenal gland, gonads, spleen, ventromedial hypothalamus and pituitary gonadotroph cells. Combined approaches of targeted mutagenesis in mice and examination of the effects of naturally occurring mutations in humans have clarified the role of SF1 in steroidogenesis and development. Targeted disruption of SF1 (FTZF1) in mice prevents gonadal and adrenal development and causes male-to-female sex reversal. A heterozygous loss-of-function human SF1 mutation (G35E) was described in a patient with adrenal failure and complete 46,XY sex reversal, indicating that haploinsufficiency of this transcription factor is sufficient to cause a severe clinical phenotype. In an infant with a similar clinical phenotype, a homozygous SF1 mutation (R92Q) was identified. In functional assays, this mutant SF1 protein exhibited partial loss of DNA binding and transcriptional activity when compared with the more severe G35E P-box mutant. These patients reveal the exquisite sensitivity of SF1-dependent developmental pathways to gene dosage and function in humans.

Adrenal Glands↗
PubMed2003

Dax1 regulates testis cord organization during gonadal differentiation.

Mutations of the DAX1 nuclear receptor gene cause adrenal hypoplasia congenita, an X-linked disorder characterized by adrenal insufficiency and hypogonadotropic hypogonadism. Targeted deletion of Dax1 in mice also reveals primary testicular dysgenesis, which is manifest by obstruction of the rete testis by Sertoli cells and hyperplastic Leydig cells, leading to seminiferous tubule dilation and degeneration of germ cells. Because Dax1 is expressed early in gonadal development, and because Sertoli and Leydig cells are located ectopically in the adult, we hypothesized that these testis abnormalities are the result of an early defect in testis development. In Dax1(-/Y) males, the gonad develops normally until 12.5 dpc. However, by 13.5 dpc, the testis cords are disorganized and incompletely formed in Dax1-deficient mice. The number of germ and Sertoli cells is unchanged, and the expression of Sertoli-specific markers appears to be normal. However, the number of peritubular myoid cells, which normally surround the testis cords, is reduced. BrdU labeling of peritubular myoid cells is low, consistent with decreased proliferation. The basal lamina produced by peritubular myoid and Sertoli cells is disrupted, leading to open and incompletely formed testis cords. Leydig cells, which normally reside in the peritubular space and extend from the coelomic surface to the dorsal surface of the gonad, are restricted to the coelomic surface of Dax1-deficient testis. We conclude that Dax1 plays a crucial role in testis differentiation by regulating the development of peritubular myoid cells and the formation of intact testis cords. The developmental abnormalities in the Dax1-deficient testis lay the foundation for gonadal dysgenesis and infertility in adult mice and, potentially in humans with DAX1 mutations.

Animals↗
PubMed2003

Battle of the sexes: new insights into genetic pathways of gonadal development.

Sex determination is governed by a series of genetic switches that influence cell fate and differentiation during critical periods of gonadal development. Remarkably, the primordial fetal gonad is bipotential. Therefore, gonadal development provides an excellent opportunity to identify genes involved in differential organogenesis. The identification of the testis-determining gene, SRY (Sex-reversed on the Y), was a pivotal first step towards unraveling this genetic pathway. It is now clear that numerous other genes, in addition to SRY, are necessary for normal testis development. For example, human mutations in a variety of genes (SOX9, WT1, SF1) impair testis development. Murine models provide evidence for additional genes (Lhx9, Emx2, M33, Dmrt, Fgf9). This lecture will highlight insights gleaned from human mutations in the nuclear receptors, SF1 (Steroidogenic Factor1) (NR5A1) and DAX1 (Dosage-sensitive sex reversal, Adrenal hypoplasia congenita, X chromosome) (NR0B1). These studies reveal the exquisite sensitivity of SF1-dependent developmental pathways to gene dosage and function in humans.

Adrenal Glands↗