Human SRY inhibits beta-catenin-mediated transcription

Gonadal sex determination in vertebrates: rethinking established mechanisms

Sex determination and differentiation are fundamental processes that are not only essential for fertility but also influence the development of many other organs, and hence, are important for species diversity and survival. In mammals, sex is determined by the inheritance of an X or a Y chromosome from the father. The Y chromosome harbours the testis-determining gene SRY, and it has long been thought that its absence is sufficient for ovarian development. Consequently, the ovarian pathway has been treated as a default pathway, in the sense that ovaries do not have or need a female-determining factor. Recently, a female-determining factor has been identified in mouse as the master regulator of ovarian development. Interestingly, this scenario was predicted as early as 1983. In this Review, we discuss the model predicted in 1983, how the mechanisms and genes currently known to be important for sex determination and differentiation in mammals have changed or supported this model, and finally, reflect on what these findings might mean for sex determination in other vertebrates.

Functional analysis of SRY variants in individuals with 46,XY differences of sex development

In mammals, male sexual development is initiated by the expression of the Sex-determining-Region-Y (SRY) gene. SRY contains a highly conserved high mobility group (HMG) box essential for DNA binding and activity. Variants in SRY cause Differences of Sex Development (DSD), accounting for 10-15% of 46, XY gonadal dysgenesis cases. Here, we present the functional analysis of five SRY coding variants identified in patients with 46, XY DSD. Four variants (p.Asp58Glu, p.Arg75Lys, p.Met85Thr, and p.Arg86Ter) are located within the HMG box and one variant (p.Tyr198Cysfs∗18) located in the C-terminal domain. We functionally characterise the impact of these variants in vitro, investigating SRY localisation and transactivational activity using SOX9 regulatory elements that are responsive to SRY. We find that three variants (p.Met85Thr, p.Arg86Ter, and p.Tyr198Cysfs∗18) have reduced or abolished transactivational activity suggesting these are pathogenic, with the p.Arg86Ter variant undetectable in our assays and the p.Met85Thr variant exhibiting reduced nuclear localisation. The pathogenic mechanisms underlying reduced activity of the novel elongated p.Tyr198Cysfs∗18 variant is however unclear, although this variant also affected localisation. In contrast, two additional variants (p.Asp58Glu and p.Arg75Lys) had no discernible effects on nuclear localisation or transactivational activity despite in silico analysis predicting impaired DNA binding. Taken together, our data establish the likely pathogenicity of these SRY variants and improve diagnostic certainty for the patients in which they were identified.

Early Gonadal Development and Sex Determination in Mammal

Sex determination is crucial for the transmission of genetic information through generations. In mammal, this process is primarily regulated by an antagonistic network of sex-related genes beginning in embryonic development and continuing throughout life. Nonetheless, abnormal expression of these sex-related genes will lead to reproductive organ and germline abnormalities, resulting in disorders of sex development (DSD) and infertility. On the other hand, it is possible to predetermine the sex of animal offspring by artificially regulating sex-related gene expression, a recent research hotspot. In this paper, we reviewed recent research that has improved our understanding of the mechanisms underlying the development of the gonad and primordial germ cells (PGCs), progenitors of the germline, to provide new directions for the treatment of DSD and infertility, both of which involve manipulating the sex ratio of livestock offspring.

Towards improved genetic diagnosis of human differences of sex development

Despite being collectively among the most frequent congenital developmental conditions worldwide, differences of sex development (DSD) lack recognition and research funding. As a result, what constitutes optimal management remains uncertain. Identification of the individual conditions under the DSD umbrella is challenging and molecular genetic diagnosis is frequently not achieved, which has psychosocial and health-related repercussions for patients and their families. New genomic approaches have the potential to resolve this impasse through better detection of protein-coding variants and ascertainment of under-recognized aetiology, such as mosaic, structural, non-coding or epigenetic variants. Ultimately, it is hoped that better outcomes data, improved understanding of the molecular causes and greater public awareness will bring an end to the stigma often associated with DSD.

Structural basis for nuclear import selectivity of pioneer transcription factor SOX2

SOX (SRY-related HMG-box) transcription factors perform critical functions in development and cell differentiation. These roles depend on precise nuclear trafficking, with mutations in the nuclear targeting regions causing developmental diseases and a range of cancers. SOX protein nuclear localization is proposed to be mediated by two nuclear localization signals (NLSs) positioned within the extremities of the DNA-binding HMG-box domain and, although mutations within either cause disease, the mechanistic basis has remained unclear. Unexpectedly, we find here that these two distantly positioned NLSs of SOX2 contribute to a contiguous interface spanning 9 of the 10 ARM domains on the nuclear import adapter IMPα3. We identify key binding determinants and show this interface is critical for neural stem cell maintenance and for Drosophila development. Moreover, we identify a structural basis for the preference of SOX2 binding to IMPα3. In addition to defining the structural basis for SOX protein localization, these results provide a platform for understanding how mutations and post-translational modifications within these regions may modulate nuclear localization and result in clinical disease, and also how other proteins containing multiple NLSs may bind IMPα through an extended recognition interface.

The SOX2 pioneer transcription factor performs critical roles in pluripotency and self-renewal of embryonic stem cells. Here the authors show that SOX2’s two nuclear localization signal sequences form a contiguous binding interface on the nuclear import receptor importin-α3, and provide a structural basis for the preference of SOX2 binding to IMPα3.

Oestrogen regulates SOX9 bioavailability by rapidly activating ERK1/2 and stabilising microtubules in a human testis-derived cell line

Nuclear SOX9 is essential for Sertoli cell differentiation and the development of a testis. Exposure of Sertoli cells to exogenous oestrogen causes cytoplasmic retention of SOX9, inhibiting testis development and promoting ovarian development. The cytoplasmic localisation of SOX9 requires a stabilised microtubule network and a key MAPK complex, ERK1/2, is responsive to oestrogen and known to affect the microtubule network. We hypothesised that oestrogen could stabilise microtubules through the activation of ERK1/2 to promote the cytoplasmic retention of SOX9. Treatment of human testis-derived NT2/D1 cells for 30 min with oestrogen rapidly activated ERK1/2, stabilised the microtubule network and increased cytoplasmic localisation of SOX9. The effects of oestrogen on SOX9 and tubulin were blocked by the ERK1/2 inhibitor U0126, demonstrating that ERK1/2 mediates the stabilisation of microtubules and cytoplasmic retention of SOX9 by oestrogen. Together, these data revealed a previously unknown mechanism for oestrogen in impacting MAPK signalling to block SOX9 bioavailability and the differentiation of Sertoli cells.

Exogenous Oestrogen Impacts Cell Fate Decision in the Developing Gonads: A Potential Cause of Declining Human Reproductive Health

The increasing incidence of testicular dysgenesis syndrome-related conditions and overall decline in human fertility has been linked to the prevalence of oestrogenic endocrine disrupting chemicals (EDCs) in the environment. Ectopic activation of oestrogen signalling by EDCs in the gonad can impact testis and ovary function and development. Oestrogen is the critical driver of ovarian differentiation in non-mammalian vertebrates, and in its absence a testis will form. In contrast, oestrogen is not required for mammalian ovarian differentiation, but it is essential for its maintenance, illustrating it is necessary for reinforcing ovarian fate. Interestingly, exposure of the bi-potential gonad to exogenous oestrogen can cause XY sex reversal in marsupials and this is mediated by the cytoplasmic retention of the testis-determining factor SOX9 (sex-determining region Y box transcription factor 9). Oestrogen can similarly suppress SOX9 and activate ovarian genes in both humans and mice, demonstrating it plays an essential role in all mammals in mediating gonad somatic cell fate. Here, we review the molecular control of gonad differentiation and explore the mechanisms through which exogenous oestrogen can influence somatic cell fate to disrupt gonad development and function. Understanding these mechanisms is essential for defining the effects of oestrogenic EDCs on the developing gonads and ultimately their impacts on human reproductive health.

Estrogen suppresses SOX9 and activates markers of female development in a human testis-derived cell line

Background

The increasing incidence of reproductive disorders in humans has been attributed to in utero exposure to estrogenic endocrine disruptors. In particular, exposure of the developing testis to exogenous estrogen can negatively impact male reproductive health. To determine how estrogens impact human gonad function, we treated the human testis-derived cell line NT2/D1 with estrogen and examined its impact on SOX9 and the expression of key markers of granulosa (ovarian) and Sertoli (testicular) cell development.

Results

Estrogen successfully activated its cognate receptor (estrogen receptor alpha; ESR1) in NT2/D1 cells. We observed a significant increase in cytoplasmic SOX9 following estrogen treatment. After 48 h of estrogen exposure, mRNA levels of the key Sertoli cell genes SOX9, SRY, AMH, FGF9 and PTGDS were significantly reduced. This was followed by a significant increase in mRNA levels for the key granulosa cell genes FOXL2 and WNT4 after 96 h of estrogen exposure.

Conclusions

These results are consistent with estrogen's effects on marsupial gonads and show that estrogen has a highly conserved impact on gonadal cell fate decisions that has existed in mammals for over 160 million years. This effect of estrogen presents as a potential mechanism contributing to the significant decrease in male fertility and reproductive health reported over recent decades. Given our widespread exposure to estrogenic endocrine disruptors, their effects on SOX9 and Sertoli cell determination could have considerable impact on the adult testis.

Inhibition of Human Y Chromosome Gene, SRY, Promotes Naïve State of Human Pluripotent Stem Cells

Although males and females have a variety of sexually dimorphic features related to hormonal effects, the genetic basis of dimorphism relies on early embryo development. Two pluripotent states, naïve and primed, emerge during early mammalian development. Identification of signaling pathways that induce differences between these two states can help to modulate conversion of primed cells to naïve cells. Naïve cells have a shorter doubling time and longer survival than their primed counterparts when passaged as single cells. In this study, we sought to explore the role of Y chromosome genes on human pluripotent stem cells (hPSCs) by investigating differential expressions of the male-specific region of the Y chromosome (MSY) genes in primed and naïve cells. Interestingly, we found that several MSY genes, including SRY, showed higher expression levels in primed compared to naïve human embryonic stem cells (hESCs). We hypothesize that SRY prevents WNT/β-catenin signaling by its interaction and inhibition of β-catenin activation in the nucleus. Results of the loss-of-function approach conducted by depletion of SRY indicated increased expressions of pluripotency marker genes and alkaline phosphatase (ALP) activity in the primed cells. SRY reduction was associated with overexpression of WNT signaling target genes AXIN2, Brachury, TCF1, TBX2, and TBX3. We suggest that inhibition of SRY may result in activation of β-catenin and up-regulation of the WNT signaling pathway, both of which are important to naïve conversion.

Doxycycline Masks the Genuine Effect of the Doxycycline-Inducible Transgene by Promoting Dopaminergic Neuron Differentiation from Human Pluripotent Stem Cells

Doxycycline (DOX), an antibacterial drug, has been widely used in the inducible gene expression system. However, its effect was largely ignored when studying functions of the inducible transgene. By using a DOX-inducible Tet-ON system, we identified that DOX alone dramatically promoted dopaminergic (DA) neuron differentiation from human pluripotent stem cells (hPSCs), whereas the studied gene had no significant effects after considering the confounding factor DOX. These findings suggest that the effect of DOX should be taken into consideration when it is used in the inducible system especially during DA neuron differentiation from hPSCs. Meanwhile, it also suggests that DOX can be used as an efficient and inexpensive molecule to increase DA neuron differentiation efficacy from hPSCs for cell therapy.

SOX3 can promote the malignant behavior of glioblastoma cells

PURPOSE

Glioblastoma is the most common and lethal adult brain tumor. Despite current therapeutic strategies, including surgery, radiation and chemotherapy, the median survival of glioblastoma patients is 15 months. The development of this tumor depends on a sub-population of glioblastoma stem cells governing tumor propagation and therapy resistance. SOX3 plays a role in both normal neural development and carcinogenesis. However, little is known about its role in glioblastoma. Thus, the aim of this work was to elucidate the role of SOX3 in glioblastoma.

METHODS

SOX3 expression was assessed using real-time quantitative PCR (RT-qPCR), Western blotting and immunohistochemistry. MTT, immunocytochemistry and Transwell assays were used to evaluate the effects of exogenous SOX3 overexpression on the viability, proliferation, migration and invasion of glioblastoma cells, respectively. The expression of Hedgehog signaling pathway components and autophagy markers was assessed using RT-qPCR and Western blot analyses, respectively.

RESULTS

Higher levels of SOX3 expression were detected in a subset of primary glioblastoma samples compared to those in non-tumoral brain tissues. Exogenous overexpression of this gene was found to increase the proliferation, viability, migration and invasion of glioblastoma cells. We also found that SOX3 up-regulation was accompanied by an enhanced activity of the Hedgehog signaling pathway and by suppression of autophagy in glioblastoma cells. Additionally, we found that SOX3 expression was elevated in patient-derived glioblastoma stem cells, as well as in oncospheres derived from glioblastoma cell lines, compared to their differentiated counterparts, implying that SOX3 expression is associated with the undifferentiated state of glioblastoma cells.

CONCLUSION

From our data we conclude that SOX3 can promote the malignant behavior of glioblastoma cells.

A transcriptomic comparison of theca and granulosa cells in chicken and cattle follicles reveals ESR2 as a potential regulator of CYP19A1 expression in the theca cells of chicken follicles

Previous studies have shown that theca and granulosa cell layers in follicles do not play the same roles in mammals and birds, especially regarding the synthesis of estrogen. The functions of these two cell types have been well characterized in cattle, but they remain unclear in chickens. To clarify this issue, a comparison of small yellow follicles (SYFs) in chickens and cattle at different follicular development stages was done by weighted gene co-expression network analysis (WGCNA). The modules obtained from WGCNA were used for further identification of the key genes associated with CYP19A1 expression. Module preservation analysis showed high similarity between cow_D (the follicular phase before the LH surge) and chicken_SYF (small yellow follicle between 6 and 8 mm in diameter) datasets, and 10 top hub genes highly associated with CYP19A1 expression in chicken SYFs were identified in each module. A comparison of the transcriptomes of theca and granulosa cells (TCs and GCs) between chicken SYFs and cattle follicles at the differentiation stage, as well as the aforementioned hub genes, revealed that ESR2 is a potential regulator of CYP19A1 expression in the theca cells of chicken SYFs. Furthermore, 197 cell-specific (179 in theca and 18 in granulosa) and 235 cell-biased expressed genes (196 in theca and 39 in granulosa) in chicken small yellow follicles were also identified by transcriptomic comparison of theca and granulosa cells.

MicroRNA dynamics at the onset of primordial germ and somatic cell sex differentiation during mouse embryonic gonad development

In mammals, commitment and specification of germ cell lines involves complex programs that include sex differentiation, control of proliferation, and meiotic initiation. Regulation of these processes is genetically controlled by fine-tuned mechanisms of gene regulation in which microRNAs (miRNAs) are involved. We have characterized, by small-RNA-seq and bioinformatics analyses, the miRNA expression patterns of male and female mouse primordial germ cells (PGCs) and gonadal somatic cells at embryonic stages E11.5, E12.5, and E13.5. Differential expression analyses revealed differences in the regulation of key miRNA clusters such as miR-199-214, miR-182-183-96, and miR-34c-5p, whose targets have defined roles during gonadal sexual determination in both germ and somatic cells. Extensive analyses of miRNA sequences revealed an increase in noncanonical isoforms on PGCs at E12.5 and dramatic changes of 3' isomiR expression and 3' nontemplate nucleotide additions in female PGCs at E13.5. Additionally, RT-qPCR analyses of genes encoding proteins involved in miRNA biogenesis and 3' nucleotide addition uncovered sexually and developmentally specific expression, characterized by the decay of Drosha, Dgcr8, and Xpo5 expression along gonadal development. These results demonstrate that miRNAs, their isomiRs, and miRNA machinery are differentially regulated and participate actively in gonadal sexual differentiation in both PGCs and gonadal somatic cells.

Distinct epigenetic signatures elucidate enhancer-gene relationships that delineate CIMP and non-CIMP colorectal cancers

Epigenetic changes, like DNA methylation, affect gene expression and in colorectal cancer (CRC), a distinct phenotype called the CpG island methylator phenotype (“CIMP”) has significantly higher levels of DNA methylation at so-called “Type C loci” within the genome. We postulate that enhancer-gene pairs are coordinately controlled through DNA methylation in order to regulate the expression of key genes/biomarkers for a particular phenotype.

Firstly, we found 24 experimentally-validated enhancers (VISTA enhancer browser) that contained statistically significant (FDR-adjusted q-value of <0.01) differentially methylated regions (DMRs) (1000bp) in a study of CIMP versus non-CIMP CRCs. Of these, the methylation of 2 enhancers, 1702 and 1944, were found to be very well correlated with the methylation of the genes Wnt3A and IGDCC3, respectively, in two separate and independent datasets.

We show for the first time that there are indeed distinct and dynamic changes in the methylation pattern of specific enhancer-gene pairs in CRCs. Such a coordinated epigenetic event could be indicative of an interaction between (1) enhancer 1702 and Wnt3A and (2) enhancer 1944 and IGDCC3. Moreover, our study shows that the methylation patterns of these 2 enhancer-gene pairs can potentially be used as biomarkers to delineate CIMP from non-CIMP CRCs.

Altered SOX9 genital tubercle enhancer region in hypospadias

Human mutations in the SOX9 gene or its regulatory region can disrupt testicular development, leading to disorders of sex development (DSDs). Our previous work involving the genomic analysis of isolated DSD patients revealed a 78kb minimal sex determining region (RevSex) far upstream of SOX9 that was duplicated in 46,XX and deleted in 46,XY DSDs. It was postulated that RevSex contains a gonadal enhancer. However, the most highly conserved sub-region within RevSex, called SR4, was neither responsive to sex determining factors in vitro nor active in the gonads of transgenic mice, suggesting that SR4 may not be functioning as a testicular enhancer. Interestingly, SR4 transgenic mice showed reporter activity in the genital tubercle, the primordium of the penis and clitoris, a previously unreported domain of Sox9 expression. SOX9 protein was detected in the genital tubercle, notably in the urethral plate epithelium, preputial glands, ventral surface ectoderm and corpus cavernosa. SR4 may therefore function as a Sox9 genital tubercle enhancer, mutations of which could possibly lead to hypospadias, a birth defect seen in the DSD patients in the RevSex study. SR4 activity and the observed SOX9 expression pattern suggest that SR4 may function as a Sox9 genital tubercle enhancer. However, conditional ablation of Sox9 in the genital tubercle using Shh-Cre/+;Sox9^flox/flox mice revealed no genital tubercle abnormalities, possibly due to compensation by similar Sox factors. To conclude, we have identified a novel regulatory enhancer driving Sox9 expression during external genitalia development.

Genetic Syndromes Affecting Kidney Development

Renal anomalies are common birth defects that may manifest as a wide spectrum of anomalies from hydronephrosis (dilation of the renal pelvis and calyces) to renal aplasia (complete absence of the kidney(s)). Aneuploidies and mosaicisms are the most common syndromes associated with CAKUT. Syndromes with single gene and renal developmental defects are less common but have facilitated insight into the mechanism of renal and other organ development. Analysis of underlying genetic mutations with transgenic and mutant mice has also led to advances in our understanding of mechanisms of renal development.

Sry and SoxE genes: How they participate in mammalian sex determination and gonadal development?

In mammals, sex determination defines the differentiation of the bipotential genital ridge into either testes or ovaries. Sry, the mammalian Y-chromosomal testis-determining gene, is a master regulator of male sex determination. It acts to switch the undifferentiated genital ridge towards testis development, triggering the adoption of a male fate. Sry initiates a cascade of gene networks through the direct regulation of Sox9 expression and promotes supporting cell differentiation, Leydig cell specification, vasculature formation and testis cord development. In the absence of Sry, alternative genetic cascades, including female sex-determining genes RSPO1, Wnt4/β-catenin and Foxl2, are involved in the formation of female genitalia and the maintenance of female ovarian development. The mutual antagonisms between male and female sex-determining pathways are crucial in not just the initiation but also the maintenance of the somatic sex of the gonad throughout the organism's lifetime. Any imbalances in above sex-determining genes can cause disorders of sex development in humans and mice. In this review, we provide a detailed summary of the expression profiles, biochemical properties and developmental functions of Sry and SoxE genes in embryonic testis development and adult gonadal development. We also briefly summarize the dedicate balances between male and female sex-determining genes in mammalian sex development, with particular highlights on the molecular actions of Sry and Sox9 transcription factors.

Molecular mechanisms associated with 46,XX disorders of sex development

In the female gonad, distinct signalling pathways activate ovarian differentiation while repressing the formation of testes. Human disorders of sex development (DSDs), such as 46,XX DSDs, can arise when this signalling is aberrant. Here we review the current understanding of the genetic mechanisms that control gonadal development, with particular emphasis on those that drive or inhibit ovarian differentiation. We discuss how disruption to these molecular pathways can lead to 46,XX disorders of ovarian development. Finally, we look at recently characterized novel genes and pathways that contribute and speculate how advances in technology will aid in further characterization of normal and disrupted human ovarian development.

Methods for the Study of Gonadal Development

Current knowledge on gonadal development and sex determination is the product of many decades of research involving a variety of scientific methods from different biological disciplines such as histology, genetics, biochemistry, and molecular biology. The earliest embryological investigations, followed by the invention of microscopy and staining methods, were based on histological examinations. The most robust development of histological staining techniques occurred in the second half of the nineteenth century and resulted in structural descriptions of gonadogenesis. These first studies on gonadal development were conducted on domesticated animals; however, currently the mouse is the most extensively studied species. The next key point in the study of gonadogenesis was the advancement of methods allowing for the in vitro culture of fetal gonads. For instance, this led to the description of the origin of cell lines forming the gonads. Protein detection using antibodies and immunolabeling methods and the use of reporter genes were also invaluable for developmental studies, enabling the visualization of the formation of gonadal structure. Recently, genetic and molecular biology techniques, especially gene expression analysis, have revolutionized studies on gonadogenesis and have provided insight into the molecular mechanisms that govern this process. The successive invention of new methods is reflected in the progress of research on gonadal development.

SOX family transcription factors involved in diverse cellular events during development

In metazoa, SOX family transcription factors play many diverse roles. In vertebrate, they are well-known regulators of numerous developmental processes. Wide-ranging studies have demonstrated the co-expression of SOX proteins in various developing tissues and that they occur in an overlapping manner and show functional redundancy. In particular, studies focusing on the HMG box of SOX proteins have revealed that the HMG box regulates DNA-binding properties, and mediates both the nucleocytoplasmic shuttling of SOX proteins and their physical interactions with partner proteins. Posttranslational modifications are further implicated in the regulation of the transcriptional activities of SOX proteins. In this review, we discuss the underlying molecular mechanisms involved in the SOX-partner factor interactions and the functional modes of SOX-partner complexes during development. We particularly emphasize the representative roles of the SOX group proteins in major tissues during developmental and physiological processes.

Crosstalk between SOXB1 proteins and WNT/β-catenin signaling in NT2/D1 cells

During early vertebrate embryogenesis, the expression of SOXB1 proteins is precisely regulated by a number of different mechanisms, including Wnt/β-catenin signaling. This is essential for controlling the balance between stemness and differentiation in embryonic stem cells. In the present study, we analyzed the molecular mechanism of LiCl action in NT2/D1 cells and examined the crosstalk between SOXB1 proteins and Wnt signaling in this model system. We have shown that LiCl increases β-catenin level, induces its translocation to the nucleus and consequently up-regulates β-catenin/Tcf-dependent transcription in NT2/D1 cells. Our results also suggest that LiCl treatment leads to increased expression of SOX2 and SOX3 proteins in NT2/D1 cells through activation of canonical Wnt signaling. Finally, we have detected a negative feedback loop between β-catenin and SOX2 expression in NT2/D1 cells. Since β-catenin and SOX2 have been linked to processes of self-renewal and pluripotency, our results have implications for future research on the maintenance of stemness and lineage commitment of embryonic stem cells.

R-spondin1, WNT4, and the CTNNB1 signaling pathway: strict control over ovarian differentiation

Sex differentiation is a unique developmental process. Starting from a bipotential gonad, it gives rise to the ovary and the testis, two highly specialized organs that differ morphologically and physiologically despite sharing common reproductive and endocrine functions. This highlights the specific plasticity of the gonadal precursors and the existence of complex antagonistic genetic regulation. Mammalian sex determination is controlled by paternal transmission of the Y-linked gene, sex-determining region Y (SRY). Using mouse models, it has been shown that the main role of Sry is to activate the expression of the transcription factor Sox9; either one of these two genes is necessary and sufficient to allow testicular development through Sertoli cell differentiation. Thus, defects in SRY/Sry and/or SOX9/Sox9 expression result in male-to-female sex reversal of XY individuals. Molecular mechanisms governing ovarian differentiation remained unknown for a long time, until the discovery of the roles of R-spondin1 (RSPO1) and WNT4. In XX individuals, activation of the β-catenin signaling pathway by the secreted proteins RSPO1 and WNT4 is required to allow granulosa cell differentiation and, in turn, ovarian differentiation. Thus, mutations in RSPO1 result in female-to-male sex reversal of XX patients, and mouse models have allowed the identification of genetic cascades activated by RSPO1 and WNT4 to regulate ovarian development. In this review, we will discuss the respective roles of RSPO1, WNT4, and the β-catenin signaling pathway during ovarian differentiation in mice.

FOXL2: a central transcription factor of the ovary

Forkhead box L2 (FOXL2) is a gene encoding a forkhead transcription factor preferentially expressed in the ovary, the eyelids and the pituitary gland. Its germline mutations are responsible for the blepharophimosis ptosis epicanthus inversus syndrome, which includes eyelid and mild craniofacial defects associated with primary ovarian insufficiency. Recent studies have shown the involvement of FOXL2 in virtually all stages of ovarian development and function, as well as in granulosa cell (GC)-related pathologies. A central role of FOXL2 is the lifetime maintenance of GC identity through the repression of testis-specific genes. Recently, a highly recurrent somatic FOXL2 mutation leading to the p.C134W subtitution has been linked to the development of GC tumours in the adult, which account for up to 5% of ovarian malignancies. In this review, we summarise data on FOXL2 modulators, targets, partners and post-translational modifications. Despite the progresses made thus far, a better understanding of the impact of FOXL2 mutations and of the molecular aspects of its function is required to rationalise its implication in various pathophysiological processes.

Quercetin reduces pluripotency, migration and adhesion of human teratocarcinoma cell line NT2/D1 by inhibiting Wnt/β-catenin signaling

In human teratocarcinoma cell line NT2/D1 quercetin exerts its anticancer effect through the inhibition of Wnt signaling.

Inherited human sex reversal due to impaired nucleocytoplasmic trafficking of SRY defines a male transcriptional threshold

Human testis determination is initiated by SRY (sex determining region on Y chromosome). Mutations in SRY cause gonadal dysgenesis with female somatic phenotype. Two subtle variants (V60L and I90M in the high-mobility group box) define inherited alleles shared by an XY sterile daughter and fertile father. Whereas specific DNA binding and bending are unaffected in a rat embryonic pre-Sertoli cell line, the variants exhibited selective defects in nucleocytoplasmic shuttling due to impaired nuclear import (V60L; mediated by Exportin-4) or export (I90M; mediated by chromosome region maintenance 1). Decreased shuttling limits nuclear accumulation of phosphorylated (activated) SRY, in turn reducing occupancy of DNA sites regulating Sertoli-cell differentiation [the testis-specific SRY-box 9 (Sox9) enhancer]. Despite distinct patterns of biochemical and cell-biological perturbations, V60L and I90M each attenuated Sox9 expression in transient transfection assays by twofold. Such attenuation was also observed in studies of V60A, a clinical variant associated with ovotestes and hence ambiguity between divergent cell fates. This shared twofold threshold is reminiscent of autosomal syndromes of transcription-factor haploinsufficiency, including XY sex reversal associated with mutations in SOX9. Our results demonstrate that nucleocytoplasmic shuttling of SRY is necessary for robust initiation of testicular development. Although also characteristic of ungulate orthologs, such shuttling is not conserved among rodents wherein impaired nuclear export of the high-mobility group box and import-dependent phosphorylation are compensated by a microsatellite-associated transcriptional activation domain. Human sex reversal due to subtle defects in the nucleocytoplasmic shuttling of SRY suggests that its transcriptional activity lies near the edge of developmental ambiguity.

Just how conserved is vertebrate sex determination?

BACKGROUND

Sex determination in vertebrate embryos has long been equated with gonadal differentiation into testes or ovaries. This view has been challenged over the years by reports of somatic sexual dimorphisms pre-dating gonadal sex differentiation. The recent finding that sex determination in birds is likely to be partly cell autonomous has again called for a broader definition of sex determination. Inherent sexual differentiation in each and every cell may apply widely among vertebrates, and may involve more than one "master sex gene" on a sex chromosome. At the gonadal level, key genes required for proper sexual differentiation are conserved among vertebrates, but their relative positions in the ovarian and testicular cascades differ.

RESULTS

We illustrate these differences by comparing key sex genes in fishes versus birds and mammals, with emphasis on DM domain genes and the SOX9-AMH pathway in the testis and the FOXL2-Aromatase pathway in the ovary. Such comparisons facilitate the identification of ancient versus derived genes involved in gonadal sex determination.

CONCLUSIONS

The data indicate that vertebrate sex-determining cascades are not as conserved as once thought.

WNT4 and RSPO1 together are required for cell proliferation in the early mouse gonad

The gonad arises from the thickening of the coelomic epithelium and then commits into the sex determination process. Testis differentiation is activated by the expression of the Y-linked gene Sry, which promotes cell proliferation and differentiation of Sertoli cells, the supporting cells of the testis. In absence of Sry (XX individuals), activation of WNT/CTNNB1 signalling, via the upregulation of Rspo1 and Wnt4, promotes ovarian differentiation. However, Rspo1 and Wnt4 are expressed in the early undifferentiated gonad of both sexes, and Axin2-lacZ, a reporter of canonical WNT/CTNNB1 signalling, is expressed in the coelomic region of the E11.5 gonadal primordium, suggesting a role of these factors in early gonadal development. Here, we show that simultaneous ablation of Rspo1 and Wnt4 impairs proliferation of the cells of the coelomic epithelium, reducing the number of progenitors of Sertoli cells in XY mutant gonads. As a consequence, in XY Wnt4(-/-); Rspo1(-/-) foetuses, this leads to the differentiation of a reduced number of Sertoli cells and the formation of a hypoplastic testis exhibiting few seminiferous tubules. Hence, this study identifies Rspo1 and Wnt4 as two new regulators of cell proliferation in the early gonad regardless of its sex, in addition to the specific role of these genes in ovarian differentiation.

β-catenin/Tcf-signaling appears to establish the murine ovarian surface epithelium (OSE) and remains active in selected postnatal OSE cells

Background

Wnts are a family of secreted signaling molecules involved in a number of developmental processes including the establishment of cell fate, polarity and proliferation. Recent studies also implicate wnts in epithelial adult stem cell maintenance, renewal and differentiation. Wnts transduce their signal through one of three signaling pathways. The best studied, the wnt/β-catenin pathway, leads to an increase in intracellular β-catenin which acts as a co-transcription factor with members of the Tcf/Lef family. A number of wnts are expressed in the ovary, specifically in the membrana granulosa and ovarian surface epithelium (OSE). We investigated the spatio-temporal pattern of β-catenin/Tcf expression in the OSE using responsive transgenic (TopGal) mice.

Results

The generated β-galactosidase response (lacZ⁺) identified the cell population that overlies the medio-lateral surface of the indifferent gonad at embryonic day (E) 11.5. From E12.5 onwards, lacZ expression disappeared in cells covering the testis but remained with ovary development. LacZ⁺ OSE cells were present throughout embryonic and postnatal ovarian development but demonstrated an age-dependent decrease to a small proportion when animals were weaned and remained at this proportion with aging. Flow cytometric (FACS) and ovarian section analyses showed lacZ⁺ cells constitute approximately 20% of OSE in postnatal (day 1) mice which fell to 8% in 5 day-old animals while in prepubertal and adult mice this accounted for only 0.2% of OSE. Apoptosis was undetected in OSE of neonates and β-catenin/Tcf-signaling cells were proliferative in neonatal mice indicating that neither cell death nor proliferation failure was responsible for the proportion alteration. It appeared that lacZ⁺ cells give rise to lacZ^- cells and this was confirmed in cell cultures. The DNA-binding dye DyeCycle Violet was used to set up the side population (SP) assay aimed at identifying subpopulations of OSE cells with chemoresistance phenotype associated with ABCG2 transporter activity. FACS analysis revealed lacZ⁺ cells exhibit cytoprotective mechanisms as indicated by enrichment within the SP.

Conclusions

The study raises the possibility that wnt/β-catenin-signaling cells constitute a progenitor cell population and could underlie the pronounced histopathology observed for human ovarian cancer.

SRY protein function in sex determination: thinking outside the box

Even though the mammalian sex-determining gene Sry has been intensively studied for the two decades since its discovery, the regions outside the conserved HMG box DNA-binding domain have received less attention due to a lack of sequence conservation and of obvious structural/functional motifs. Here, we summarize the available evidence for function beyond the HMG box, identify the known and postulated biochemical functions of the non-HMG-box domains in sex determination, and present possible explanations for the puzzling diversity of these non-HMG-box domains.

Mechanical stretch enhances COL2A1 expression on chromatin by inducing SOX9 nuclear translocalization in inner meniscus cells

The meniscus plays an important role in controlling the biomechanics of the knee. However, the mechanical stress-related response in meniscus cells remains unclear. We investigated mechanical stretch-regulated gene expression in human meniscus cells. Human inner and outer meniscus cells were prepared from the inner and outer halves of the lateral meniscus. The gene expressions of Sry-type HMG box (SOX) 9 and α1(II) collagen (COL2A1) were assessed by real-time PCR analyses after cyclic tensile strain (CTS) treatment (0.5 Hz, 5% stretch). The localization and phosphorylation of SOX9 were evaluated by immunohistochemical and Western blot (WB) analyses. Chromatin immunoprecipitation (IP) analysis was performed to assess the stretch-related protein-DNA complex formation between SOX9 and the COL2A1 enhancer on chromatin. Type II collagen deposition and SOX9 production were detected only in inner menisci. CTS treatments increased expression of the COL2A1 and SOX9 genes in inner meniscus cells, but not in outer meniscus cells. In addition, CTS treatments stimulated nuclear translocalization and phosphorylation of SOX9 in inner meniscus cells. Chromatin IP analyses revealed that CTS increased the association between SOX9 and its DNA-binding site, included in the COL2A1 enhancer, on chromatin. Our results indicate that inner and outer meniscus cells have different properties in mechanical stretch-induced COL2A1 expression. In inner meniscus cells, mechanical stretch may have an essential role in the epigenetic regulation of COL2A1 expression.

Wnt signaling in ovarian development inhibits Sf1 activation of Sox9 via the Tesco enhancer

Genome analysis of patients with disorders of sex development, and gain- and loss-of-function studies in mice indicate that gonadal development is regulated by opposing signals. In females, the Wnt/β-catenin canonical pathway blocks testicular differentiation by repressing the expression of the Sertoli cell-specific gene Sox9 by an unknown mechanism. Using cell and embryonic gonad culture models, we show that activation of the Wnt/β-catenin pathway inhibits the expression of Sox9 and Amh, whereas mRNA and protein levels of Sry and steroidogenic factor 1 (Sf1), two key transcriptional regulators of Sox9, are not altered. Ectopic activation of Wnt/β-catenin signaling in male gonads led to a loss of Sf1 binding to the Tesco enhancer and absent Sox9 expression that we also observed in wild-type ovaries. Moreover, ectopic Wnt/β-catenin signaling induced the expression of the female somatic cell markers, Bmp2 and Rspo1, as a likely consequence of Sox9 loss. Wnt/β-catenin signaling in XY gonads did not, however, affect gene expression of the steroidogenic Leydig cell Sf1 target gene, Cyp11a1, or Sf1 binding to the Cyp11a1 promoter. Our data support a model in ovary development whereby activation of β-catenin prevents Sf1 binding to the Sox9 enhancer, thereby inhibiting Sox9 expression and Sertoli cell differentiation.

Sox9 gene regulation and the loss of the XY/XX sex-determining mechanism in the mole vole Ellobius lutescens

In most mammals, the Y chromosomal Sry gene initiates testis formation within the bipotential gonad, resulting in male development. SRY is a transcription factor and together with SF1 it directly up-regulates the expression of the pivotal sex-determining gene Sox9 via a 1.3-kb cis-regulatory element (TESCO) which contains an evolutionarily conserved region (ECR) of 180 bp. Remarkably, several rodent species appear to determine sex in the absence of Sry and a Y chromosome, including the mole voles Ellobius lutescens and Ellobius tancrei, whereas Ellobius fuscocapillus of the same genus retained Sry. The sex-determining mechanisms in the Sry-negative species remain elusive. We have cloned and sequenced 1.1 kb of E. lutescens TESCO which shares 75% sequence identity with mouse TESCO indicating that testicular Sox9 expression in E. lutescens might still be regulated via TESCO. We have also cloned and sequenced the ECRs of E. tancrei and E. fuscocapillus. While the three Ellobius ECRs are highly similar (94-97% sequence identity), they all display a 14-bp deletion (Δ14) removing a highly conserved SOX/TCF site. Introducing Δ14 into mouse TESCO increased both basal activity and SF1-mediated activation of TESCO in HEK293T cells. We propose a model whereby Δ14 may have triggered up-regulation of Sox9 in XX gonads leading to destabilization of the XY/XX sex-determining mechanism in Ellobius. E. lutescens/E. tancrei and E. fuscocapillus could have independently stabilized their sex determination mechanisms by Sry-independent and Sry-dependent approaches, respectively.

Identification and functional analysis of SOX10 missense mutations in different subtypes of Waardenburg syndrome

Waardenburg syndrome (WS) is a rare disorder characterized by pigmentation defects and sensorineural deafness, classified into four clinical subtypes, WS1-S4. Whereas the absence of additional features characterizes WS2, association with Hirschsprung disease defines WS4. WS is genetically heterogeneous, with six genes already identified, including SOX10. About 50 heterozygous SOX10 mutations have been described in patients presenting with WS2 or WS4, with or without myelination defects of the peripheral and central nervous system (PCWH, Peripheral demyelinating neuropathy-Central dysmyelinating leukodystrophy-Waardenburg syndrome-Hirschsprung disease, or PCW, PCWH without HD). The majority are truncating mutations that most often remove the main functional domains of the protein. Only three missense mutations have been thus far reported. In the present study, novel SOX10 missense mutations were found in 11 patients and were examined for effects on SOX10 characteristics and functions. The mutations were associated with various phenotypes, ranging from WS2 to PCWH. All tested mutations were found to be deleterious. Some mutants presented with partial cytoplasmic redistribution, some lost their DNA-binding and/or transactivation capabilities on various tissue-specific target genes. Intriguingly, several mutants were redistributed in nuclear foci. Whether this phenomenon is a cause or a consequence of mutation-associated pathogenicity remains to be determined, but this observation could help to identify new SOX10 modes of action.

A case of SRY-positive 38,XY true hermaphroditism (XY sex reversal) in a cat

Investigation of abnormal sexual development in companion animals can allow for the elimination of inherited disorders from breeding populations while contributing to the understanding of the complex process of mammalian sexual development and differentiation. A 1-year-old mixed-breed cat, presented for neutering, was tentatively diagnosed as a male with bilateral cryptorchidism. During surgery, the surgeon identified gonads in an ovarian position and a complete bicornuate uterus. Both testicular and ovarian architecture in the gonads and Mullerian and Wolffian duct derivatives were identified histologically. The karyotype was that of a normal male (38,XY), and no causative mutation was identified in the feline SRY coding sequence amplified from genomic DNA. All features of the case were compatible with a diagnosis of SRY-positive 38,XY sex reversal, true hermaphrodite phenotype. To the authors' knowledge, this is the first report of this disorder in a domestic cat.

The Sry3 Y chromosome locus elevates blood pressure and renin-angiotensin system indexes

BACKGROUND

Sex-determining region Y (Sry) is a transcription factor. Our research group has shown that there are multiple copies of Sry in Wistar-Kyoto (WKY) and spontaneous hypertensive (SHR) rats, and that they have novel functions separate from testes determination.

OBJECTIVE

We hypothesized that exogenously delivered Sry3 to the normotensive WKY male kidney would activate the renin-angiotensin system (RAS) and raise blood pressure (BP), based on previous in vitro studies.

METHODS

Sry3 or control vector was electroporated to the left kidney of male WKY rats and the following measurements were taken: BP by telemetry, renin-angiotensin measures by radioimmunoassay, plasma and tissue catecholamines by HPLC with electrochemical detection, sodium by flame photometry, and inulin by ELISA.

RESULTS

Sry3 increased BP 10 to 20 mm Hg compared with controls (P < 0.01) and produced a significant 40% decrease in urine sodium compared with controls (P < 0.05). Sry3 increased renal angiotensin II and plasma renin activity by >100% compared with controls (P < 0.01 and P < 0.05, respectively).

CONCLUSION

The findings presented here confirm and extend the argument for Sry3 as one of the genes responsible for the SHR hypertensive Y chromosome phenotype and are consistent with increased tissue RAS activity due to Sry3 and increased sodium reabsorption.

Failure of SOX9 regulation in 46XY disorders of sex development with SRY, SOX9 and SF1 mutations

BACKGROUND

In human embryogenesis, loss of SRY (sex determining region on Y), SOX9 (SRY-related HMG box 9) or SF1 (steroidogenic factor 1) function causes disorders of sex development (DSD). A defining event of vertebrate sex determination is male-specific upregulation and maintenance of SOX9 expression in gonadal pre-Sertoli cells, which is preceded by transient SRY expression in mammals. In mice, Sox9 regulation is under the transcriptional control of SRY, SF1 and SOX9 via a conserved testis-specific enhancer of Sox9 (TES). Regulation of SOX9 in human sex determination is however poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

We show that a human embryonal carcinoma cell line (NT2/D1) can model events in presumptive Sertoli cells that initiate human sex determination. SRY associates with transcriptionally active chromatin in NT2/D1 cells and over-expression increases endogenous SOX9 expression. SRY and SF1 co-operate to activate the human SOX9 homologous TES (hTES), a process dependent on phosphorylated SF1. SOX9 also activates hTES, augmented by SF1, suggesting a mechanism for maintenance of SOX9 expression by auto-regulation. Analysis of mutant SRY, SF1 and SOX9 proteins encoded by thirteen separate 46,XY DSD gonadal dysgenesis individuals reveals a reduced ability to activate hTES.

CONCLUSIONS/SIGNIFICANCE

We demonstrate how three human sex-determining factors are likely to function during gonadal development around SOX9 as a hub gene, with different genetic causes of 46,XY DSD due a common failure to upregulate SOX9 transcription.

Sry: the master switch in mammalian sex determination

SRY, the mammalian Y-chromosomal testis-determining gene, induces male sex determination. Recent studies in mice reveal that the major role of SRY is to achieve sufficient expression of the related gene Sox9, in order to induce Sertoli cell differentiation, which in turn drives testis formation. Here, we discuss the cascade of events triggered by SRY and the mechanisms that reinforce the differentiation of the testes in males while actively inhibiting ovarian development.

Genetic mechanisms underlying male sex determination in mammals

Genetic control of gonadal development proceeds through either the male or female molecular pathways, driving bipotential gonadal anlage differentiation into a testis or ovary. Antagonistic interactions between the 2 pathways determine the gonadal sex. Essentially sex determination is the enhancement of one of the 2 pathways according to genetic sex. Initially, Sry with other factors upregulates Sox9 expression in XY individuals. Afterwards the expression of Sox9 is maintained by a positive feedback loop with Fgf9 and prostaglandin D2 as well as by autoregulative ability of Sox9. If these factors reach high concentrations, then Sox9 and/or Fgf9 may inhibit the female pathway. Surprisingly, splicing, nuclear transport, and extramatrix proteins may be involved in sex determination. The male sex determination pathway switches on the expression of genes driving Sertoli cell differentiation. Sertoli cells orchestrate testicular differentiation. In the absence of Sry, the predomination of the female pathway results in the realization of a robust genetic program that drives ovarian differentiation.

Epigenetic gene silencing by the SRY protein is mediated by a KRAB-O protein that recruits the KAP1 co-repressor machinery

The sex determination transcription factor SRY is a cell fate-determining transcription factor that mediates testis differentiation during embryogenesis. It may function by repressing the ovarian determinant gene, RSPO1, action in the ovarian developmental pathway and activates genes, such as SOX9, important for testis differentiation at the onset of gonadogenesis. Further, altered expression of SRY and related SOX genes contribute to oncogenesis in many human cancers. Little is known of the mechanisms by which SRY regulates its target genes. Recently a KRAB domain protein (KRAB-O) that lacks a zinc finger motif has been demonstrated to interact with SRY and hypothesized to function as an adaptor molecule for SRY by tethering the KAP1-NuRD-SETDB1-HP1 silencing machinery to repress SRY targets. We have critically examined this hypothesis by reconstituting and characterizing SRY-KRAB-O-KAP1 interactions. These recombinant molecules can form a ternary complex by direct and high affinity interactions. The KRAB-O protein can simultaneously bind KAP1 and SRY in a noncompetitive but also noncooperative manner. An extensive mutagenesis analysis suggests that different surfaces on KRAB-O are utilized for these independent interactions. Transcriptional repression by SRY requires binding to KRAB-O, thus bridging to the KAP1 repression machinery. This repression machinery is recruited to SRY target promoters in chromatin templates via SRY. These results suggest that SRY has co-opted the KRAB-O protein to recruit the KAP1 repression machinery to sex determination target genes. Other KRAB domain proteins, which lack a zinc finger DNA-binding motif, may function in similar roles as adaptor proteins for epigenetic gene silencing.

Interactions between SOX factors and Wnt/beta-catenin signaling in development and disease

The SOX family of transcription factors have emerged as modulators of canonical Wnt/beta-catenin signaling in diverse development and disease contexts. There are over 20 SOX proteins encoded in the vertebrate genome and recent evidence suggests that many of these can physically interact with beta-catenin and modulate the transcription of Wnt-target genes. The precise mechanisms by which SOX proteins regulate beta-catenin/TCF activity are still being resolved and there is evidence to support a number of models including: protein-protein interactions, the binding of SOX factors to Wnt-target gene promoters, the recruitment of co-repressors or co-activators, modulation of protein stability, and nuclear translocation. In some contexts, Wnt signaling also regulates SOX expression resulting in feedback regulatory loops that fine-tune cellular responses to beta-catenin/TCF activity. In this review, we summarize the examples of Sox-Wnt interactions and examine the underlying mechanisms of this potentially widespread and underappreciated mode of Wnt-regulation.