A transgenic insertion upstream of sox9 is associated with dominant XX sex reversal in the mouse

Transcriptional regulation of the FSH receptor: new perspectives

The cell-surface receptor for the gonadotropin follicle-stimulating hormone (FSH) is expressed exclusively on Sertoli cells of the testis and granulosa cells of the ovary. FSH signal transduction through its receptor (Fshr) is critical for the timing and maintenance of normal gametogenesis in the mammalian gonad. In the 13 years since the gene encoding Fshr was first cloned, the mechanisms controlling its transcription have been extensively examined, but a clear understanding of what drives its unique cell-specificity remains elusive. Current knowledge of basal Fshr transcription highlights the role of an E-box in the proximal promoter which is bound by the basic helix-loop-helix transcription factors upstream stimulatory factor 1 (Usf1) and Usf2. Recent studies utilizing knockout mice and chromatin immunoprecipitation validated the importance of Usf to Fshr transcription and demonstrated a sexually dimorphic requirement for the Usf proteins to maintain normal Fshr expression. Studies have also shown that the promoter region itself is insufficient for appropriate Fshr expression in transgenic mice, indicating Fshr transcription depends on regulatory elements that lie outside of the promoter. Identification of such elements has been propelled by recent availability of genome sequence data, which facilitated studies using comparative genomics, DNase I hypersensitivity mapping, and transgenic analysis with large fragments of DNA. This review will focus on the current understanding of transcriptional regulatory processes that control expression of rat Fshr, including recent advances from our laboratory.

Distal regulatory elements are required for Fshr expression, in vivo

The gonadotropin follicle-stimulating hormone (FSH) is required for initiation and maintenance of normal gametogenesis and acts through a specific, cell-surface receptor (Fshr) present only on Sertoli and granulosa cells in the gonads. Despite extensive examination of the transcriptional mechanisms regulating Fshr, the sequences directing its expression to these cells remain unidentified. To establish the minimal region necessary for Fshr expression, we generated transgenic mice carrying a yeast artificial chromosome (YAC) that contained 413 kilobases (kb) of the rat Fshr locus (YAC60). Transgene expression, as determined by RT-PCR, was absent from immature testis and Sertoli cells, limited to germ cells of the adult testis, and never observed in the ovary. While the data is limited to only one transgenic line, it suggests that the 413kb region does not specify the normal spatiotemporal expression pattern of Fshr. Comparative genomics was used to identify potential distal regulatory elements, revealing seven regions of high evolutionary conservation (>80% identity over 100bp or more), six of which were absent from the transgene. Functional examination of the evolutionary conserved regions (ECRs) by transient transfection revealed that all of the ECRs had modest transcriptional activity in Sertoli or myoid cells with two, ECR4 and ECR5, showing differential effects in expressing and non-expressing cells. These data reveal that distal regulatory regions (outside the 413kb in YAC60) are required for appropriate temporal and spatial Fshr expression and implicate the identified ECRs in transcriptional regulation of Fshr.

Immunohistochemical Analysis of Sox9 in Ovarian Sertoli Cell Tumors and Other Tumors in the Differential Diagnosis

The distinction of ovarian Sertoli cell tumor from other tumors in the histological differential diagnosis, particularly endometrioid carcinoma and carcinoid tumor, may be difficult. Many immunohistochemical markers have been studied for this differential diagnosis, but currently available markers are neither 100% sensitive nor specific. Sox9 is a transcription factor involved in Sertoli cell differentiation in the testis. The role that this molecule plays in the pathogenesis of ovarian Sertoli cell tumors and the potential use as an immunohistochemical marker for differential diagnosis have not been investigated. Immunohistochemical staining for Sox9 was performed in 152 ovarian tumors: pure Sertoli cell tumor (n = 36), endometrioid borderline tumor (n = 38), well-differentiated endometrioid carcinoma (n = 26), sertoliform endometrioid carcinoma (n = 13), and carcinoid tumor (n = 39). Nuclear expression was considered positive. Extent and intensity of staining were semiquantitatively scored. In addition, immunohistochemical composite scores in positive cases (ranging from 1 to 12) were calculated based on the extent score multiplied by the intensity score. Sox9 was expressed in 44% of Sertoli cell tumors, 55% of endometrioid borderline tumors, 65% of well-differentiated endometrioid carcinomas, 39% of sertoliform endometrioid carcinomas, and 10% of carcinoid tumors. The mean Sox9 immunohistochemical composite scores in positive cases were 6.3 for Sertoli cell tumor, 5.3 for endometrioid borderline tumor, 8.0 for well-differentiated endometrioid carcinoma, 2.8 for sertoliform endometrioid carcinoma, and 6.8 for carcinoid tumor. The differences in the mean Sox9 composite scores between Sertoli cell tumor and the other tumor categories were not statistically significant (p values ranged from 0.092 to 0.523). We conclude that Sox9 is variably expressed in ovarian Sertoli cell tumor and other tumors that are in the differential diagnosis and, thus, is not helpful for immunohistochemical distinction. Understanding the role of Sox9 in the pathogenesis of ovarian Sertoli cell tumor requires further study.

Balancing the bipotential gonad between alternative organ fates: a new perspective on an old problem

The embryonic gonads give rise to one of two morphologically and functionally different organs, a testis or an ovary. Sex determination is the embryonic process that determines the developmental fate of the gonad. In mammals, sex determination is regulated by a DNA binding protein encoded on the Y chromosome, Sry, and it's downstream mediator, Sox9, which trigger testis determination in the bipotential gonad. However, evidence suggests that the extracellular signals. Fgf9 and Wnt4, are also required to establish divergent organogenesis of the gonad. In this review, we discuss how these extracellular signals interface with cell-autonomous factors to determine the fate of the mammalian gonad, and we derive a model that could provide a molecular explanation for testis determination in vertebrates where Sry is absent.

R-spondin1 is essential in sex determination, skin differentiation and malignancy

R-spondins are a recently characterized small family of growth factors. Here we show that human R-spondin1 (RSPO1) is the gene disrupted in a recessive syndrome characterized by XX sex reversal, palmoplantar hyperkeratosis and predisposition to squamous cell carcinoma of the skin. Our data show, for the first time, that disruption of a single gene can lead to complete female-to-male sex reversal in the absence of the testis-determining gene, SRY.

Dosage-dependent rescue of definitive nephrogenesis by a distant Gata3 enhancer

Human GATA3 haploinsufficiency leads to HDR (hypoparathyroidism, deafness and renal dysplasia) syndrome, demonstrating that the development of a specific subset of organs in which this transcription factor is expressed is exquisitely sensitive to gene dosage. We previously showed that murine GATA-3 is essential for definitive kidney development, and that a large YAC transgene faithfully recapitulated GATA-3 expression in the urogenital system. Here we describe the localization and activity of a kidney enhancer (KE) located 113 kbp 5' to the Gata3 structural gene. When the KE was employed to direct renal system-specific GATA-3 transcription, the extent of cell autonomous kidney rescue in Gata3-deficient mice correlated with graded allelic expression of transgenic GATA-3. These data demonstrate that a single distant, tissue-specific enhancer can direct GATA-3 gene expression to confer all embryonic patterning information that is required for successful execution of metanephrogenesis, and that the dosage of GATA-3 required has a threshold between 50% and 70% of diploid activity.

Conserved distances between vertebrate highly conserved elements

High numbers of sequence element with very high (>95%) sequence conservation between the human and other vertebrate genomes have been reported and ascribed putative cis-regulatory functions. We have investigated the structural relationships between such elements in mammalian genomes and find that not only their sequences, but also the distances between them are significantly (P<2.2x10(-16)) more conserved than corresponding distances between orthologous protein-coding genes or between exons within these genes. Regions of largely conserved distance between consecutive highly conserved elements (HCE) generally overlap previously identified HCE clusters, but may be far longer (up to 20 Mb) and possibly cover close to 25% of the human genome sequence. Similar conservation of distance is found between bird (chicken) and mammalian genomes and is also discernible in comparisons between fish and mammals. The data suggest either that a substantial amount of essential (functionally active) elements with lower sequence conservation occupy the space between the HCEs or that distance itself is an important factor in transcriptional regulation or chromatin modelling.

The road to maleness: from testis to Wolffian duct

The establishment of the male internal reproductive system involves two crucial events: the formation of the testis and the maintenance and differentiation of the Wolffian duct. Testis formation, particularly the specification of Sertoli cell and Leydig cell lineages, is controlled strictly by genetic components initiated by the testis-determining gene SRY (sex-determining region of the Y chromosome). Conversely, Wolffian duct differentiation is not directly mediated via the composition of the sex chromosome or SRY; instead, it relies on androgens derived from the Leydig cells. Leydig cells do not express SRY, indicating that a crosstalk must be present between the SRY-positive Sertoli and Leydig cells to ensure normal androgen production. Recent advancement of genetic and genomic approaches has unveiled the molecular pathways for differentiation of Sertoli cells and Leydig cells as well as development of the Wolffian duct.

The Wilms tumor gene, Wt1, is required for Sox9 expression and maintenance of tubular architecture in the developing testis

Mutation of the transcription factor and tumor suppressor gene WT1 results in a range of genitourinary anomalies in humans, including 46,XY gonadal dysgenesis, indicating that WT1 plays a critical role in sex determination. However, because knockout of Wt1 in mice results in apoptosis of the genital ridge, it is unknown whether WT1 is required for testis development after the initial steps of sex determination. To address this question, we generated a mouse strain carrying a Wt1 conditional knockout allele and ablated Wt1 function specifically in Sertoli cells by embryonic day 14.5, several days after testis determination. Wt1 knockout resulted in disruption of developing seminiferous tubules and subsequent progressive loss of Sertoli cells and germ cells such that postnatal mutant testes were almost completely devoid of these cell types and were severely hypoplastic. Thus, Wt1 is essential for the maintenance of Sertoli cells and seminiferous tubules in the developing testes. Of particular note, expression of the testis-determining gene Sox9 in mutant Sertoli cells was turned off at embryonic day 14.5 after Wt1 ablation, suggesting that WT1 regulates Sox9, either directly or indirectly, after Sry expression ceases. Our data, along with previous work demonstrating the role of Wt1 at early stages of gonadal development, thus indicate that Wt1 is essential at multiple steps in testicular development.

Sox9 in testis determination

Sox9 is an Sry-box-containing gene that encodes a transcriptional activator. During mouse gonadogenesis, Sox9 is detected in the male gonad at 11.5 days postcoitus (dpc). At 12.5 dpc, testicular cords form, morphologically distinguishing the male gonad from the ovary. From this stage onwards, Sox9 expression is restricted to the Sertoli cell lineage and persists in the adult. Humans with heterozygous mutations in SOX9 develop a skeletal syndrome known as campomelic dysplasia. Furthermore, most XY SOX9 heterozygotes show variable male-to-female sex reversal, implicating SOX9 in testis development. Sox9 heterozygous knockout mice die at birth with a syndrome similar to that of human campomelic dysplasia. In contrast to humans, XY Sox9+/- mice form normal appearing testes. Germ-line knockout of Sox9 using a conditional null allele provides a tool for generating Sox9-/- mice by simple genetic crosses. However, Sox9-/- mice die soon after 11.5 dpc because of cardiovascular defects. In vitro culture of the urogenital ridges of XY Sox9-/- results in gonads lacking testicular cords and Sertoli cell marker expression, but with the expression of ovarian-specific markers. Therefore, Sox9 is essential for diverting an intrinsically ovarian program of organogenesis toward testis formation.

The makings of maleness: towards an integrated view of male sexual development

As the mammalian embryo develops, it must engage one of the two distinct programmes of gene activity, morphogenesis and organogenesis that characterize males and females. In males, sexual development hinges on testis determination and differentiation, but also involves many coordinated transcriptional, signalling and endocrine networks that underpin the masculinization of other organs and tissues, including the brain. Here we bring together current knowledge about these networks, identify gaps in the overall picture, and highlight the known defects that lead to disorders of male sexual development.

A microarray analysis of the XX Wnt4 mutant gonad targeted at the identification of genes involved in testis vascular differentiation

One of the earliest morphological changes during testicular differentiation is the establishment of an XY specific vasculature. The testis vascular system is derived from mesonephric endothelial cells that migrate into the gonad. In the XX gonad, mesonephric cell migration and testis vascular development are inhibited by WNT4 signaling. In Wnt4 mutant XX gonads, endothelial cells migrate from the mesonephros and form a male-like coelomic vessel. Interestingly, this process occurs in the absence of other obvious features of testis differentiation, suggesting that Wnt4 specifically inhibits XY vascular development. Consequently, the XX Wnt4 mutant mice presented an opportunity to focus a gene expression screen on the processes of mesonephric cell migration and testicular vascular development. We compared differences in gene expression between XY Wnt4+/+ and XX Wnt4+/+ gonads and between XX Wnt4+/+ and XX Wnt4+/+ gonads to identify sets of genes similarly upregulated in wildtype XY gonads and XX mutant gonads or upregulated in XX gonads as compared to XY gonads and XX mutant gonads. We show that several genes identified in the first set are expressed in vascular domains, and have predicted functions related to cell migration or vascular development. However, the expression patterns and known functions of other genes are not consistent with roles in these processes. This screen has identified candidates for regulation of sex specific vascular development, and has implicated a role for WNT4 signaling in the development of Sertoli and germ cell lineages not immediately obvious from previous phenotypic analyses.

Fgf9 and Wnt4 act as antagonistic signals to regulate mammalian sex determination

The genes encoding members of the wingless-related MMTV integration site (WNT) and fibroblast growth factor (FGF) families coordinate growth, morphogenesis, and differentiation in many fields of cells during development. In the mouse, Fgf9 and Wnt4 are expressed in gonads of both sexes prior to sex determination. Loss of Fgf9 leads to XY sex reversal, whereas loss of Wnt4 results in partial testis development in XX gonads. However, the relationship between these signals and the male sex-determining gene, Sry, was unknown. We show through gain- and loss-of-function experiments that fibroblast growth factor 9 (FGF9) and WNT4 act as opposing signals to regulate sex determination. In the mouse XY gonad, Sry normally initiates a feed-forward loop between Sox9 and Fgf9, which up-regulates Fgf9 and represses Wnt4 to establish the testis pathway. Surprisingly, loss of Wnt4 in XX gonads is sufficient to up-regulate Fgf9 and Sox9 in the absence of Sry. These data suggest that the fate of the gonad is controlled by antagonism between Fgf9 and Wnt4. The role of the male sex-determining switch--Sry in the case of mammals--is to tip the balance between these underlying patterning signals. In principle, sex determination in other vertebrates may operate through any switch that introduces an imbalance between these two signaling pathways.

Sex determination and sex reversal

Sex determination in mammals is based on a genetic cascade that controls the fate of the gonads. Gonads will then direct the establishment of phenotypic sex through the production of hormones. Different types of sex reversal are expected to occur if mutations disrupt one of the three steps of gonadal differentiation: formation of the gonadal primordia, sex determination, and testis or ovary development.

FGF9 promotes survival of germ cells in the fetal testis

In addition to its role in somatic cell development in the testis, our data have revealed a role for Fgf9 in XY germ cell survival. In Fgf9-null mice, germ cells in the XY gonad decline in numbers after 11.5 days post coitum (dpc), while germ cell numbers in XX gonads are unaffected. We present evidence that germ cells resident in the XY gonad become dependent on FGF9 signaling between 10.5 dpc and 11.5 dpc, and that FGF9 directly promotes XY gonocyte survival after 11.5 dpc, independently from Sertoli cell differentiation. Furthermore, XY Fgf9-null gonads undergo true male-to-female sex reversal as they initiate but fail to maintain the male pathway and subsequently express markers of ovarian differentiation(Fst and Bmp2). By 14.5 dpc, these gonads contain germ cells that enter meiosis synchronously with ovarian gonocytes. FGF9 is necessary for 11.5 dpc XY gonocyte survival and is the earliest reported factor with a sex-specific role in regulating germ cell survival.

Identification of cis-regulatory elements for MECP2 expression

Rett syndrome (RTT) is an X-linked dominant disabling neurodevelopmental disorder caused by loss of function mutations in the MECP2 gene, located at Xq28, which encodes a multifunctional protein. MECP2 expression is regulated in a developmental stage and cell-type-specific manner. The need for tightly controlled MeCP2 levels in brain is strongly suggested by neurologically abnormal phenotypes of mouse models with mild overexpression and by mental retardation in human males with MECP2 duplication. We set out to identify long-range cis-regulatory sequences that differentially regulate MECP2 transcription and, when mutated, may contribute to the pathogenesis of RTT, autism or X-linked mental retardation. By inter-species sequence comparisons, we detected 27 highly conserved non-coding DNA sequences within a 210 kb region covering MECP2. We functionally confirmed four enhancer and two silencer elements by performing luciferase reporter assays in four different human cell lines. The transcription factor binding capability of the identified regulatory elements was tested by gel shift assays. To locate the human MECP2 core promoter, we dissected the promoter region by reporter assays with deletion constructs. We then used chromosome conformation capture methods to document long-range interactions of three enhancers and two silencers with the MECP2 promoter. Acting over distances of up to 130 kb, these elements may influence chromatin configurations and regulate MECP2 transcription. Our study has defined the "MECP2 functional expression module" and identified enhancer and silencer elements that are likely to be responsible for the tissue-specific, developmental stage-specific or splice-variant-specific control of MeCP2 protein expression.

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

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

Ancient duplicated conserved noncoding elements in vertebrates: a genomic and functional analysis

Fish-mammal genomic comparisons have proved powerful in identifying conserved noncoding elements likely to be cis-regulatory in nature, and the majority of those tested in vivo have been shown to act as tissue-specific enhancers associated with genes involved in transcriptional regulation of development. Although most of these elements share little sequence identity to each other, a small number are remarkably similar and appear to be the product of duplication events. Here, we searched for duplicated conserved noncoding elements in the human genome, using comparisons with Fugu to select putative cis-regulatory sequences. We identified 124 families of duplicated elements, each containing between two and five members, that are highly conserved within and between vertebrate genomes. In 74% of cases, we were able to assign a specific set of paralogous genes with annotation relating to transcriptional regulation and/or development to each family, thus removing much of the ambiguity in identifying associated genes. We find that duplicate elements have the potential to up-regulate reporter gene expression in a tissue-specific manner and that expression domains often overlap, but are not necessarily identical, between family members. Over two thirds of the families are conserved in duplicate in fish and appear to predate the large-scale duplication events thought to have occurred at the origin of vertebrates. We propose a model whereby gene duplication and the evolution of cis-regulatory elements can be considered in the context of increased morphological diversity and the emergence of the modern vertebrate body plan.

Comparative proteomic analysis to study molecular events during gonad development in mice

Sex determination represents a critical bifurcation in the road of embryonic development. It is based on a finely regulated network of gene activity, as well as protein-protein interactions and activation or silencing of signaling pathways. Despite the identification of a number of critical genes, many aspects of the molecular cascade that drives the differentiation of the embryonic gonad into either a testis or an ovary remain poorly understood. To identify new proteins involved in this cascade, we employed two-dimensional gel electrophoresis and mass spectrometry to compare the protein expression profiles of fetal mouse testes and ovaries. Three proteins, hnRPA1, TRA1, and HSC71, were found to be expressed in a male-specific manner and this expression was confirmed by real-time reverse transcriptase polymerase chain reaction (RT-PCR) and in situ hybridization. Moreover, HSC71 was found to be hyperphosphorylated in male compared to female gonads, emphasizing the advantage of the proteomic approach in allowing the detection of posttranslational modifications.

Mechanisms of Disease: normal and abnormal gonadal development and sex determination in mammals

Sex differentiation in mammals occurs in three steps. The first is the establishment of chromosomal sex at fertilization, followed by the differentiation of the gonad into an ovary or testis, and finally the establishment of the phenotypic sex of the embryo and adult, which is regulated by the gonad. Disruption of any of these stages gives rise to sexual ambiguities that include 46,XY pure gonadal dysgenesis, 46,XX true hermaphroditism, and variable degrees of intersexuality. In this review, we focus on the development of the mammalian gonad from a bipotential primordium that differentiates into either an ovary or a testis. We describe the recent increase in our knowledge of the genetic defects that directly affect gonadal development, sex determination, and sex differentiation, with emphasis on the comparison of genetic studies in mice with studies of naturally occurring mutations in humans.

Association of palmoplantar keratoderma, cutaneous squamous cell carcinoma, dental anomalies, and hypogenitalism in four siblings with 46,XX karyotype: a new syndrome

The association of palmoplantar keratoderma (PPK) with the development of cutaneous squamous cell carcinomas (SCCs), dental anomalies, severe hypogenitalism with hypospadias, abnormal development of gonads with ambiguous external genitalia, gynecomastia, altered plasma sex hormones levels, and hypertriglyceridemia has not, to our knowledge, been reported previously. We describe it in 4 brothers with 46,XX karyotype, whereas the 5 sisters of their consanguineous parents were unaffected. This family may represent a new syndrome. The PPK was of the classical nonepidermolytic histologic type. The proband also had a laryngeal carcinoma diagnosed in his early forties and nodular testicular hyperplasia of Leydig cells.

Multiple Alternative Splicing and Differential Expression of dmrt1 During Gonad Transformation of the Rice Field Eel1

Morphologically distinct males and females are observed throughout the animal kingdom. Why and how sex evolved and is maintained in most living organisms remains a key question in cellular and evolutionary biology. Here we report that four isoforms of dmrt1 (dsx- and mab3-related transcription factor 1) are generated in testis, ovotestis, and ovary by alternative splicing in the rice field eel, a fresh water fish that undergoes natural sex reversal from female to male during its life cycle. These transcripts encode four different size proteins with 301, 196, 300, and 205 amino acids. Like fly doublesex splicing, the dmrt1 of the rice field eel is also alternatively spliced at the 3' region, which generates diverse isoforms in gonads by alternative use of 3' sequences. Not only is dmrt1 expressed specifically in gonads, but its multiple isoforms are differentially coexpressed in gonadal epithelium during gonad transformation. Expression levels of a and b isoforms of dmrt1 ranged from low to high (ovary < ovotestis I < ovotestis II < ovotestis III < testis), based on comparisons of mean values from real-time fluorescent quantitative reverse transcription-polymerase chain reaction analysis. The overall expression level of dmrt1 b was much lower than that of dmrt1 a. Expression of dmrt1 d was not only low, but it also did not change significantly during sex transformation. The differential expression of dmrt1 isoforms may also be regulated by their 3' untranslated regions (UTRs), although these 3' UTRs do not contribute to intracellular localization of the Dmrt1 protein. These results provide new insight into roles of regulation at the level of splicing of dmrt1 in governing the sex differentiation cascade.

XX sex reversal, palmoplantar keratoderma, and predisposition to squamous cell carcinoma: genetic analysis in one family

We describe a large inbred Sicilian family that includes four 46, XX (SRY-) brothers. Palmoplantar hyperkeratosis (PPK) and an associated predisposition to squamous cell carcinoma (SCC) of the skin, segregates as a recessive trait within the family. Interestingly, all the PPK-affected members of the family are phenotypic males (46,XY or 46,XX) while seven XX sibs are healthy phenotypic females with no signs of PPK. We propose that homozygosity for a single mutational event, possibly including contiguous genes, may cause PPK/SCC in both XY or XX individuals and sex reversal in XX individuals. The family is informative for linkage analysis for the PPK trait and allows linkage exclusion for the sex reversal trait. Here we show that 15 loci involved in PPK etiology, skin differentiation, function or malignancy, and nine loci involved in sex determination/differentiation are not implicated in the phenotype of this family.

Sertoli cell differentiation is induced both cell-autonomously and through prostaglandin signaling during mammalian sex determination

We have raised an antibody specifically recognizing endogenous mouse SRY protein and used it to investigate the molecular and cellular mode of action of SRY in testis determination. We find that expression of SRY protein closely mirrors the expression of Sry mRNA in mouse genital ridges and is detectable for 6 to 8 h after the mRNA ceases to be detectable. The subset of somatic cells that expresses SRY begins to express SOX9 almost immediately. Since these SOX9-positive cells go on to develop as Sertoli cells, it appears that SRY expression marks the pre-Sertoli cell lineage and leads to up-regulation of Sox9 expression cell-autonomously. However, a small proportion of SOX9-positive cells did not appear to express SRY, possibly reflecting the additional involvement of paracrine signaling in activating Sox9 transcription in these cells. We confirmed by ex vivo cell mixing experiments that SRY is able to engage receptor-mediated signaling to up-regulate Sox9 expression. Finally, we showed by employing specific inhibitors that the causative signaling molecule is prostaglandin D2 (PGD2) and that PGD2 can induce Sox9 transcription in cultured XX gonads. Our data indicate a mechanism whereby Sry uses both a cell-autonomous mechanism and a PGD2-mediated signaling mechanism to stimulate expression of Sox9 and induce the differentiation of Sertoli cells in vivo.

Characterization of Pisrt1/Foxl2 in Ellobius lutescens and exclusion as sex-determining genes

The rodent Ellobius lutescens is an exceptional mammal which determines male sex constitutively without the SRY gene and, therefore, may serve as an animal model for human 46,XX female-to-male sex reversal. It was suggested that other factors of the network of sex-determining genes determine maleness in these animals. However, some sex-determining genes like SOX9 and SF1 have already been excluded by segregation analysis as primary sex-determining factors in E. lutescens. In this work, we have cloned and characterized two genes of the PIS (polled intersex syndrome) gene interval, which were reported as candidates in female-to-male sex reversal in hornless goats recently. The genes Foxl2 and Pisrt1 from that interval were identified in E. lutescens DNA and mapped to Chromosome 8. We have excluded linkage of Foxl2 and Pisrt1 loci with the sex of the animals. Hence, the involvement of this gene region in sex determination may be specific for goats and is not a general mechanism of XX sex reversal or XX male sex determination.

Follicular cells acquire sertoli cell characteristics after oocyte loss

Although it has been suggested that in mammals the loss of female germ cells may induce the masculinization of the ovarian compartment, there has been as yet no conclusive demonstration. To directly address that question, the present study has been designed to determine the fate of follicular cells after oocyte loss. Using gamma-irradiation to selectively deplete oocytes in nongrowing follicles in female rats, we show that follicular cells in oocyte-depleted follicles survive, proliferate, and subsequently acquire morphological characteristics of Sertoli cells: elongated cytoplasm, basal location of the nucleus, and specific Sertoli cell junctions, the ectoplasmic specializations. These Sertoli-like cells express, however, the female-specific marker FOXL2 (Forkhead L2) but not the male sex-specific marker SOX-9 (Sry-type high-mobility-group box transcription factor-9) underlying the maintenance of molecular characteristics of granulosa cells. Before transdifferentiating into Sertoli-like cells, follicular cells of oocyte-depleted follicles initiate the expression of anti-Mullerian hormone and inhibin alpha-subunit that are typically synthesized by granulosa cells from the onset of follicular growth. Experimental modifications of the endocrine balance of the irradiated females show that there is a close relationship between plasma FSH levels and the occurrence of Sertoli-like cells. In addition to providing experimental evidence for the crucial role of the oocyte in granulosa cell phenotype maintenance, these results emphasize that the transdifferentiation of granulosa cells into Sertoli cells occurs in a multistep fashion, requiring the maturation of granulosa cells and depending on the endocrine milieu.

From SRY to SOX9: Mammalian Testis Differentiation

Sry (sex-determining region on the Y chromosome) is a master gene that initiates testis differentiation of the bipotential indifferent gonad in mammals. In mice, Sry expression is transiently activated in a center-to-pole wave along the anteroposterior (AP) axis of developing XY gonads. Shortly after the onset of Sry activation, Sox9 (Sry-related HMG box-9), a fundamental testis-differentiation gene common to all vertebrates, is also activated in a center-to-pole pattern similar to the initial Sry expression profile. Several male-specific cellular events, such as glycogenesis, coelomic epithelium proliferation, mesonephric migration and vasculogenesis, are induced in XY gonads following the onset of Sry and Sox9 expression. This paper mainly focuses on recent advances in elucidating the regulatory mechanisms of Sry and Sox9 expression and male-specific cellular events immediately downstream of SRY action during the initial phases of testis differentiation.

Temperature, genes, and sex: a comparative view of sex determination in Trachemys scripta and Mus musculus

Sex determination, the step at which differentiation of males and females is initiated in the embryo, is of central importance to the propagation of species. There is a remarkable diversity of mechanisms by which sex determination is accomplished. In general these mechanisms fall into two categories: Genetic Sex Determination (GSD), which depends on genetic differences between the sexes, and Environmental Sex Determination (ESD), which depends on extrinsic cues. In this review we will consider these two means of determining sex with particular emphasis on two species: a species that depends on GSD, Mus musculus, and a species that depends on ESD, Trachemys scripta. Because the structural organization of the adult testis and ovary is very similar across vertebrates, most biologists had expected that the pathways downstream of the sex-determining switch would be conserved. However, emerging data indicate that not only are the initial sex determining mechanisms different, but the downstream pathways and morphogenetic events leading to the development of a testis or ovary also are different.

New insights into the regulation of mammalian sex determination and male sex differentiation

In mammals, sex development is a genetically and hormonally controlled process that begins with the establishment of chromosomal or genetic sex (XY or XX) at conception. At approximately 6 to 7 weeks of human gestation or embryonic day e11.5 in the mouse, expression of the Y chromosome-linked sex determining gene called SRY (described in detail in this chapter) then initiates gonadal differentiation, which is the formation of either a testis (male) or an ovary (female). Male sex differentiation (development of internal and external reproductive organs and acquisition of male secondary sex characteristics) is then controlled by three principal hormones produced by the testis: Mullerian inhibiting substance (MIS) or anti-Mullerian hormone (AMH), testosterone, and insulin-like factor 3 (INSL3). In the absence of these critical testicular hormones, female sex differentiation ensues. This sequential, three-step process of mammalian sex development is also known as the Jost paradigm. With the advent of modern biotechnologies over the past decade, such as transgenics, array-based gene profiling, and proteomics, the field of mammalian sex determination has witnessed a remarkable boost in the understanding of the genetics and complex molecular mechanisms that regulate this fundamental biological event. Consequently, a number of excellent reviews have been devoted to this topic. The purpose of the present chapter is to provide an overview of selected aspects of mammalian sex determination and differentiation with an emphasis on studies that have marked this field of study.

A complex interaction of imprinted and maternal-effect genes modifies sex determination in Odd Sex (Ods) mice

The transgenic insertional mouse mutation Odd Sex (Ods) represents a model for the long-range regulation of Sox9. The mutation causes complete female-to-male sex reversal by inducing a male-specific expression pattern of Sox9 in XX Ods/+ embryonic gonads. We previously described an A/J strain-specific suppressor of Ods termed Odsm1(A). Here we show that phenotypic sex depends on a complex interaction between the suppressor and the transgene. Suppression can be achieved only if the transgene is transmitted paternally. In addition, the suppressor itself exhibits a maternal effect, suggesting that it may act on chromatin in the early embryo.

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

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

Silencing of Fshr occurs through a conserved, hypersensitive site in the first intron

Expression of the FSH receptor (Fshr) is restricted to testicular Sertoli cells and ovarian granulosa cells, thereby limiting the direct targets of FSH action to these somatic cells of the gonads. Earlier studies indicate that transcription of Fshr in the gonads requires elements outside the gene's immediate 5' flanking sequence. To help uncover candidate regulatory sequences, comparative genomics and deoxyribonuclease I hypersensitivity mapping were employed. A total of 156 evolutionarily conserved sequences were found, and partial deoxyribonuclease I hypersensitivity mapping across 45 kb of 5' flanking sequence and the first intron identified four hypersensitive sites, DHS1-4. Notably, DHS1 and DHS2 localized to conserved sites in the promoter region and exon 1 and correlated with the active state of the gene. DHS3 also corresponded to a conserved site (site 7) but was more pronounced in nonexpressing myoid cells, suggesting a role in gene silencing. Transient transfection analysis of DHS3 confirmed its role in gene silencing, a function that was promoter, cell type, and position dependent. Protein-DNA binding studies on DHS3 revealed that octamer transcription factor 1 (OCT-1) and GATA-4 bound site 7, in vitro, and transient transfection analysis showed that their binding sites were required for silencing activity. Furthermore, chromatin immunoprecipitation revealed that OCT-1 bound to site 7 in the endogenous gene, but only in myoid cells. In contrast, GATA-1 bound site 7 predominantly in Sertoli cells, suggesting that it attenuates silencer activity. The findings reveal that OCT-1 binds within DHS3 to silence Fshr transcription and implicate members of the GATA family in the modulation of this activity.

A novel Sry-downstream cellular event which preserves the readily available energy source of glycogen in mouse sex differentiation

Sry is transiently activated in pre-Sertoli cells of the gonadal ridge to initiate testis differentiation in mice. In pre-Sertoli cells, however, the cellular events induced immediately after the onset of Sry expression remain largely unknown. Here we show that testis-specific glycogen accumulation in pre-Sertoli cells is one of the earliest cellular events downstream of Sry action. In developing XY gonads, glycogen accumulation starts to occur in pre-Sertoli cells from around 11.15 dpc (tail somite 14 stage) in a center-to-pole pattern similar to the initial Sry expression profile. Glycogen accumulation was also found in XX male gonads of Sry-transgenic embryos, but not in XX female gonads of wildtype embryos at any developmental stage. In vitro analyses using various culture conditions suggest that testis-specific glycogen deposition is a tissue-autonomous event that can be induced even in serum-free conditions and in a culture of gonadal explants without adjacent mesonephros. Moreover, glycogen accumulation in pre-Sertoli cells was significantly inhibited in vitro by the PI3K inhibitor LY294002, but not by the MEK inhibitor PD98059. Active phospho-AKT (PI3K effector) showed a high degree of accumulation in gonadal somatic cells of genital ridges in a testis-specific manner, both in vitro and in vivo. Therefore, these findings suggest that immediately after the onset of Sry expression, activation of the PI3K-AKT pathway promotes testis-specific glycogen storage in pre-Sertoli cells. To the best of our knowledge, this is a novel Sry-downstream cellular event which preserves this readily available energy source in Sertoli cells for testis-specific morphogenesis and hormone production.

Fine mapping of chromosome 17 translocation breakpoints > or = 900 Kb upstream of SOX9 in acampomelic campomelic dysplasia and a mild, familial skeletal dysplasia

Previously, our group reported a five-generation family in which a balanced t(13;17) translocation is associated with a spectrum of skeletal abnormalities, including Robin sequence, hypoplastic scapulae, and a missing pair of ribs. Using polymerase chain reaction (PCR) with chromosome-specific markers to analyze DBA from somatic cell hybrids containing the derivative translocation chromosomes, we narrowed the breakpoint on each chromosome. Subsequent sequencing of PCR products spanning the breakpoints identified the breaks precisely. The chromosome 17 breakpoint maps approximately 932 kb upstream of the sex-determining region Y (SRY)-related high-mobility group box gene (SOX) within a noncoding transcript represented by two IMAGE cDNA clones. A growing number of reports have implicated chromosome 17 breakpoints at a distance of up to 1 Mb from SOX9 in some cases of campomelic dysplasia (CD). Although this multigeneration family has a disorder that shares some features with CD, their phenotype is significantly milder than any reported cases of (nonmosaic) CD. Therefore, this case may represent an etiologically distinct skeletal dysplasia or may be an extremely mild familial example of CD, caused by the most proximal translocation breakpoint from SOX9 reported to date. In addition, we have refined the breakpoint in a acampomelic CD case described elsewhere and have found that it lies approximately 900 kb upstream of SOX9.

Position effects due to chromosome breakpoints that map approximately 900 Kb upstream and approximately 1.3 Mb downstream of SOX9 in two patients with campomelic dysplasia

Campomelic dysplasia (CD) is a semilethal skeletal malformation syndrome with or without XY sex reversal. In addition to the multiple mutations found within the sex-determining region Y-related high-mobility group box gene (SOX9) on 17q24.3, several chromosome anomalies (translocations, inversions, and deletions) with breakpoints scattered over 1 Mb upstream of SOX9 have been described. Here, we present a balanced translocation, t(4;17)(q28.3;q24.3), segregating in a family with a mild acampomelic CD with Robin sequence. Both chromosome breakpoints have been identified by fluorescence in situ hybridization and have been sequenced using a somatic cell hybrid. The 17q24.3 breakpoint maps approximately 900 kb upstream of SOX9, which is within the same bacterial artificial chromosome clone as the breakpoints of two other reported patients with mild CD. We also report a prenatal identification of acampomelic CD with male-to-female sex reversal in a fetus with a de novo balanced complex karyotype, 46,XY,t(4;7;8;17)(4qter-->4p15.1::17q25.1-->17qter;7qter-->7p15.3::4p15.1-->4pter;8pter-->8q12.1::7p15.3-->7pter;17pter-->17q25.1::8q12.1-->8qter). Surprisingly, the 17q breakpoint maps approximately 1.3 Mb downstream of SOX9, making this the longest-range position effect found in the field of human genetics and the first report of a patient with CD with the chromosome breakpoint mapping 3' of SOX9. By using the Regulatory Potential score in conjunction with analysis of the rearrangement breakpoints, we identified a candidate upstream cis-regulatory element, SOX9cre1. We provide evidence that this 1.1-kb evolutionarily conserved element and the downstream breakpoint region colocalize with SOX9 in the interphase nucleus, despite being located 1.1 Mb upstream and 1.3 Mb downstream of it, respectively. The potential molecular mechanism responsible for the position effect is discussed.

Sox9 is sufficient for functional testis development producing fertile male mice in the absence of Sry

In the dominant mouse mutant Odd Sex, XXOds/+ mice develop as phenotypic, sterile males due to male-pattern expression of Sox9 in XXOds/+ embryonic gonads. To test whether SOX9 was sufficient to generate a fully fertile male in the absence of Sry, we constructed an XY(Sry(-))Ods/+ male mouse, in which the male phenotype is controlled autosomally by the Ods mutation. Mice were initially fertile, but progressively lost fertility until 5-6 months when they were sterile with very few germ cells in the testis. XY(Sry-)Ods/+ males also failed to establish the correct male-specific pattern of vascularization at the time of sex determination, which could be correlated to an inability of XY(Sry-),Ods/+ males to fully down-regulate Wnt4 expression in the embryonic gonad. Increasing the amount of SOX9 by producing homozygous XY(Sry-)Ods/Ods males was able to completely rescue the phenotype and restore correct vascular patterning and long-term fertility. These data indicate that activation of SOX9 in the gonad is sufficient to trigger all the downstream events needed for the development of a fully fertile male and provide evidence that Sox9 may down-regulate Wnt4 expression in the gonad.

Interspecific chromosome-wide transcription profiles reveal the existence of mammalian-specific and species-specific chromosome domains

A long-range exploration of expression levels through wide chromosome territories was carried out in three species (pig, cattle, and chicken) by aligning EST counts against the human genome. This strategy made it possible to produce expression profiles that were very similar between pig and cattle and that were significantly correlated with chicken levels of expression. In parallel with these alignments, we developed a statistical approach enabling us to screen genomic regions for both underexpression and overexpression at the chromosome level within a given species, as well as interspecifically. The observed correlations are indicative of the existence of interspecifically conserved domains of gene expression, not only for housekeeping genes (which are highly expressed), but also for regions where genes are significantly underexpressed. Furthermore, our strategy made it possible to point out regions that are differentially regulated between species. These expression data were crossed with available comparative mapping information for pigs and cattle, suggesting that coregulated regions are syntenic in various mammals.

Minireview: transcriptional regulation of gonadal development and differentiation

The embryonic gonad is undifferentiated in males and females until a critical stage when the sex chromosomes dictate its development as a testis or ovary. This binary developmental process provides a unique opportunity to delineate the molecular pathways that lead to distinctly different tissues. The testis comprises three main cell types: Sertoli cells, Leydig cells, and germ cells. The Sertoli cells and germ cells reside in seminiferous tubules where spermatogenesis occurs. The Leydig cells populate the interstitial compartment and produce testosterone. The ovary also comprises three main cell types: granulosa cells, theca cells, and oocytes. The oocytes are surrounded by granulosa and theca cells in follicles that grow and differentiate during characteristic reproductive cycles. In this review, we summarize the molecular pathways that regulate the distinct differentiation of these cell types in the developing testis and ovary. In particular, we focus on the transcription factors that initiate these cascades. Although most of the early insights into the sex determination pathway were based on human mutations, targeted mutagenesis in mouse models has revealed key roles for genes not anticipated to regulate gonadal development. Defining these molecular pathways provides the foundation for understanding this critical developmental event and provides new insight into the causes of gonadal dysgenesis.

Conserved non-genic sequences — an unexpected feature of mammalian genomes

Mammalian genomes contain highly conserved sequences that are not functionally transcribed. These sequences are single copy and comprise approximately 1-2% of the human genome. Evolutionary analysis strongly supports their functional conservation, although their potentially diverse, functional attributes remain unknown. It is likely that genomic variation in conserved non-genic sequences is associated with phenotypic variability and human disorders. So how might their function and contribution to human disorders be examined?

Multiple, distant Gata2 enhancers specify temporally and tissue-specific patterning in the developing urogenital system

Transcription factor GATA-2 is expressed in a complex temporally and tissue-specific pattern within the developing embryo. Loss-of-function studies in the mouse showed that GATA-2 activity is first required during very early hematopoiesis. We subsequently showed that a 271-kbp yeast artificial chromosome (YAC) transgene could fully complement the loss of Gata2 hematopoietic function but that these YAC-rescued Gata2 null mutant mice die perinatally due to defective urogenital development. The rescuing YAC did not display appropriate urogenital expression of Gata2, implying the existence of a urogenital-specific enhancer(s) lying outside the boundaries of this transgene. Here we outline a coupled general strategy for regulatory sequence discovery, linking bioinformatics to functional genomics based on the bacterial artificial chromosome (BAC) libraries used to generate the mouse genome sequence. Exploiting this strategy, we screened >1 Mbp of genomic DNA surrounding Gata2 for urogenital enhancer activity. We found that the spatially and tissue-specific functions for Gata2 in the developing urogenital system are conferred by at least three separate regionally and temporally specific urogenital enhancer elements, two of which reside far 3' to the Gata2 structural gene. Including the additional enhancers that were discovered using this strategy (called BAC trap) extends the functional realm of the Gata2 locus to greater than 1 Mbp.

Molecular cloning, expression ofSox5 and its down-regulation ofDmrt1 transcription in Zebrafish

The doublesex and mab-3-related transcription factor 1 (Dmrt1) is the founding member of a family of DM domain genes, involved in gonadogenesis. Here we report the cloning of zebrafish Sox5 and use real time PCR to show that its expression increases while expression of Dmrt1 decreases during embryogenesis. Characterization of the proximal promoter of zebrafish Dmrt1 revealed two positive and two negative regulatory regions and a Sox5-binding site. Co-transfection of dmrt1 (with or without the Sox-binding site), driving an EGFP reporter and Sox5 showed further that Sox5 bound the Dmrt1 promoter and inhibited Dmrt1 expression. This antagonistic partnership between Dmrt1 and Sox5 suggests a potential transcriptional regulatory mechanism for Dmrt1 in early embryogenesis.

Long-range control of gene expression: emerging mechanisms and disruption in disease

Transcriptional control is a major mechanism for regulating gene expression. The complex machinery required to effect this control is still emerging from functional and evolutionary analysis of genomic architecture. In addition to the promoter, many other regulatory elements are required for spatiotemporally and quantitatively correct gene expression. Enhancer and repressor elements may reside in introns or up- and downstream of the transcription unit. For some genes with highly complex expression patterns--often those that function as key developmental control genes--the cis-regulatory domain can extend long distances outside the transcription unit. Some of the earliest hints of this came from disease-associated chromosomal breaks positioned well outside the relevant gene. With the availability of wide-ranging genome sequence comparisons, strong conservation of many noncoding regions became obvious. Functional studies have shown many of these conserved sites to be transcriptional regulatory elements that sometimes reside inside unrelated neighboring genes. Such sequence-conserved elements generally harbor sites for tissue-specific DNA-binding proteins. Developmentally variable chromatin conformation can control protein access to these sites and can regulate transcription. Disruption of these finely tuned mechanisms can cause disease. Some regulatory element mutations will be associated with phenotypes distinct from any identified for coding-region mutations.

SOX9 is up-regulated by the transient expression of SRY specifically in Sertoli cell precursors

The Y chromosome gene Sry encodes a transcription factor required to initiate testis development. The related autosomal gene Sox9 is up-regulated shortly after the onset of Sry transcription and is thought essential for the differentiation of Sertoli cells. The lineage that gives rise to Sertoli cells has its origins within the coelomic epithelium (CE) of the genital ridge, but from cells also able to give rise to an interstitial cell type. It was not known at what point SRY acts in the derivation of this lineage or how the two genes interact. To investigate the identity of the cells expressing Sry, we designed two transgenes driven by the Sry promoter: one gives expression of a stable reporter, human placental alkaline phosphatase (hPLAP), while the second gives expression of a functional Myc-epitope tagged SRY protein (SRYMYC). Taking advantage of lasting hPLAP activity after transcription of the reporter gene has ceased, we could show that SryhPLAP was expressed exclusively in all cells fated to become Sertoli cells. SRYMYC-single-positive cells were first observed in the gonad and not in the CE. Subsequently, they became SRYMYC/SOX9-double-positive, but only for a few hours before turning into SOX9-single-positive cells. After the coelomic epithelial cells migrate into the gonad, there is first a decision to become interstitial or supporting cells, and then the transient expression of SRY in the latter determines their fate as Sertoli cells by up-regulating Sox9.

The endless quest for sex determination genes

Disorders in human sex determination cause defects in gonadal function and can result in a spectrum of abnormalities in the internal and external genitalia, ranging from relatively mild sexual ambiguities to complete sex reversal. Several genes involved in sex determination have been validated in humans, and activities of their gene products are being elucidated, particularly in mouse models. However, how these genes interact in an overall process remains far from clear, and it is probable that many additional genes are involved. Management of patients with pathologies in sex determination and subsequent differentiation is currently under debate, but will require not only an understanding of the multiple definitions of an individual's sex but also an increased knowledge of the molecular mechanisms involved in sex determination.

SOX9 is an intestine crypt transcription factor, is regulated by the Wnt pathway, and represses the CDX2 and MUC2 genes

TCF and SOX proteins belong to the high mobility group box transcription factor family. Whereas TCFs, the transcriptional effectors of the Wnt pathway, have been widely implicated in the development, homeostasis and disease of the intestine epithelium, little is known about the function of the SOX proteins in this tissue. Here, we identified SOX9 in a SOX expression screening in the mouse fetal intestine. We report that the SOX9 protein is expressed in the intestinal epithelium in a pattern characteristic of Wnt targets. We provide in vitro and in vivo evidence that a bipartite β-catenin/TCF4 transcription factor, the effector of the Wnt signaling pathway, is required for SOX9 expression in epithelial cells. Finally, in colon epithelium-derived cells, SOX9 transcriptionally represses the CDX2 and MUC2 genes, normally expressed in the mature villus cells of the intestinal epithelium, and may therefore contribute to the Wnt-dependent maintenance of a progenitor cell phenotype.

The mouse juvenile spermatogonial depletion (jsd) phenotype is due to a mutation in the X-derived retrogene, mUtp14b

The recessive juvenile spermatogonial depletion (jsd) mutation results in a single wave of spermatogenesis, followed by failure of type A spermatogonia to differentiate, resulting in adult male sterility. We have identified a jsd-specific rearrangement in the mouse homologue of the Saccharomyces cerevisiae gene UTP14, termed mUtp14b. Confirmation that mUtp14b underlies the jsd phenotype was obtained by transgenic bacterial artificial chromosome (BAC) rescue. We also identified a homologous gene on the Mus musculus X chromosome (MMUX) (mUtp14a) that is the strict homologue of the yeast gene, from which the intronless mUtp14b has been derived by retrotransposition. Expression analysis showed that mUtp14b is predominantly expressed in the germ line of the testis from zygotene through round spermatids, whereas mUtp14a, although well expressed in all somatic tissues, could be detected only in the germ line in round spermatids. In yeast, depletion of the UTP proteins impedes production of 18S rRNA, leading to cell death. We propose that the retroposed autosomal copy mUtp14b, having acquired a testis-specific expression pattern, could have provided a mechanism for increasing the efficiency and/or numbers of germ cells produced by meeting the need for more 18S rRNA and protein. Such a mechanism would be of obvious reproductive advantage and be strongly selected for in evolution. Consistent with this hypothesis is the finding of a similar X-autosome retroposition of UTP14 in human which seems to have arisen independently of that in rodents. In jsd homozygotes, which lack a functional copy of Utp14b, insufficient production of rRNA quickly leads to a cessation of spermatogenesis.

The effects of estrogen on the expression of genes underlying the differentiation of somatic cells in the murine gonad

Estrogen (17beta-estradiol, E2)-deficient aromatase knockout (ArKO) mice develop Sertoli and Leydig cells at puberty. We hypothesized that estrogen, directly or indirectly, regulates genes responsible for somatic cell differentiation and steroidogenesis. ArKO ovaries expressed estrogen receptors alpha and beta, and LH receptor, indices of estrogen responsiveness in the ovary. Wild-type (Wt) and ArKO mice received either E2 or placebo for 3 wk, from 7-10 wk of age. E2 decreased serum FSH and LH and increased uterine weights of 10-wk-old ArKO mice. We measured mRNA expression of Sertoli cell, Sry-like HMG box protein 9 (Sox9); three upstream transcription factors, liver receptor homolog-1 (Lrh-1), steroidogenic factor 1, and dosage-sensitive sex reversal adrenal hypoplasia congenital critical region on the X chromosome gene 1; and one downstream factor, Müllerian-inhibiting substance. Placebo-treated ArKO ovaries have increased Sox9 (15-fold; P < 0.001), Müllerian-inhibiting substance (2.9-fold), Lrh-1 (7.7-fold), and dosage-sensitive sex reversal adrenal hypoplasia congenital critical region on the X chromosome gene 1 (12-fold) expression compared with Wt at 10 wk. Steroidogenic factor 1 was similar to Wt. Consistent with increased serum T levels and Leydig cells in their ovaries, placebo-treated ArKO ovaries had increased 17alpha-hydroxylase, 17beta-hydroxysteroid dehydrogenase type-3, and 17beta-hydroxysteroid dehydrogenase type-1 expression compared with Wt at 10 wk. E2 treatment for 3 wk improved the ovarian phenotype, decreased development of Sertoli cells, decreased the expression of Sox9, Lrh-1, and the steroidogenic enzymes in ArKO ovaries, and induced ovulation in some cases. In conclusion, the expression of the genes regulating somatic cell differentiation is directly or indirectly responsive to estrogen.

Fgf9induces proliferation and nuclear localization of FGFR2 in Sertoli precursors during male sex determination

Recently, we demonstrated that loss of Fgf9 results in a block of testis development and a male to female sex-reversed phenotype; however, the function of Fgf9 in sex determination was unknown. We now show that Fgf9 is necessary for two steps of testis development just downstream of the male sex-determining gene, Sry: (1) for the proliferation of a population of cells that give rise to Sertoli progenitors; and (2) for the nuclear localization of an FGF receptor (FGFR2) in Sertoli cell precursors. The nuclear localization of FGFR2 coincides with the initiation of Sry expression and the nuclear localization of SOX9 during the early differentiation of Sertoli cells and the determination of male fate.