Loss of sequences 3' to the testis-determining gene, SRY, including the Y pseudoautosomal boundary associated with partial testicular determination

SOX Genes and Their Role in Disorders of Sex Development

SOX genesare master regulatory genes controlling development and are fundamental to the establishment of sex determination in a multitude of organisms. The discovery of the master sex-determining gene SRY in 1990 was pivotal for the understanding of how testis development is initiated in mammals. With this discovery, an entire family of SOX factors were uncovered that play crucial roles in cell fate decisions during development. The importance of SOX genes in human reproductive development is evident from the various disorders of sex development (DSD) upon loss or overexpression of SOX gene function. Here, we review the roles that SOX genes play in gonad development and their involvement in DSD. We start with an overview of sex determination and differentiation, DSDs, and the SOX gene family and function. We then provide detailed information and discussion on SOX genes that have been implicated in DSDs, both at the gene and regulatory level. These include SRY, SOX9, SOX3, SOX8, and SOX10. This review provides insights on the crucial balance of SOX gene expression levels needed for gonad development and maintenance and how changes in these levels can lead to DSDs.

Targeting the Non-Coding Genome for the Diagnosis of Disorders of Sex Development

Disorders of sex development (DSD) are a complex group of conditions with highly variable clinical phenotypes, most often caused by failure of gonadal development. DSD are estimated to occur in around 1.7% of all live births. Whilst the understanding of genes involved in gonad development has increased exponentially, approximately 50% of patients with a DSD remain without a genetic diagnosis, possibly implicating non-coding genomic regions instead. Here, we review how variants in the non-coding genome of DSD patients can be identified using techniques such as array comparative genomic hybridization (CGH) to detect copy number variants (CNVs), and more recently, whole genome sequencing (WGS). Once a CNV in a patient's non-coding genome is identified, putative regulatory elements such as enhancers need to be determined within these vast genomic regions. We will review the available online tools and databases that can be used to refine regions with potential enhancer activity based on chromosomal accessibility, histone modifications, transcription factor binding site analysis, chromatin conformation, and disease association. We will also review the current in vitro and in vivo techniques available to demonstrate the functionality of the identified enhancers. The review concludes with a clinical update on the enhancers linked to DSD.

Cellular fate of intersex differentiation

Infertile ovotestis (mixture of ovary and testis) often occurs in intersex individuals under certain pathological and physiological conditions. However, how ovotestis is formed remains largely unknown. Here, we report the first comprehensive single-cell developmental atlas of the model ovotestis. We provide an overview of cell identities and a roadmap of germline, niche, and stem cell development in ovotestis by cell lineage reconstruction and a uniform manifold approximation and projection. We identify common progenitors of germline stem cells with two states, which reveal their bipotential nature to differentiate into both spermatogonial stem cells and female germline stem cells. Moreover, we found that ovotestis infertility was caused by degradation of female germline cells via liquid-liquid phase separation of the proteasomes in the nucleus, and impaired histone-to-protamine replacement in spermatid differentiation. Notably, signaling pathways in gonadal niche cells and their interaction with germlines synergistically determined distinct cell fate of both male and female germlines. Overall, we reveal a cellular fate map of germline and niche cell development that shapes cell differentiation direction of ovotestis, and provide novel insights into ovotestis development.

Long-term outcomes and molecular analysis of a large cohort of patients with 46,XY disorder of sex development due to partial gonadal dysgenesis

BACKGROUND

Follow-up data on patients with 46,XY partial gonadal dysgenesis (PGD) until adulthood are scarce, making information on prognosis difficult.

OBJECTIVE

To analyse the long-term outcomes of patients with 46,XY PGD regarding testosterone production, germ cell tumour risk, genotype and psychosexual adaptation.

METHODS

A retrospective longitudinal study of 33 patients (20 assigned male and 13 patients assigned female at birth). Molecular diagnosis was performed by Sanger sequencing or by targeted massively parallel sequencing of 63 genes related to disorders of sex development (DSDs).

RESULTS

Age at first and last visit ranged from 0.1 to 43 and from 17 to 53 years, respectively. Spontaneous puberty was observed in 57% of the patients. During follow-up, six of them had a gonadectomy (four due to female gender, and two because of a gonadal tumour). At last evaluation, five of six patients had adult male testosterone levels (median 16.7 nmol/L, range 15.3-21.7 nmol/L) and elevated LH and FSH levels. Germ cell tumours were found in two postpubertal patients (one with an abdominal gonad and one patient with Frasier syndrome). Molecular diagnosis was possible in 11 patients (33%). NR5A1 variants were the most prevalent molecular defects (n = 6), and four of five patients harbouring them developed spontaneous puberty. Gender change was observed in four patients, two from each sex assignment group; all patients reported satisfaction with their gender at final evaluation. Sexual intercourse was reported by 81% of both gender and 82% of them reported satisfaction with their sexual lives.

CONCLUSION

Spontaneous puberty was observed in 57% of the patients with 46,XY PGD, being NR5A1 defects the most prevalent ones among all the patients and in those with spontaneous puberty. Gender change due to gender dysphoria was reported by 12% of the patients. All the patients reported satisfaction with their final gender, and most of them with their sexual life.

Non-coding variation in disorders of sex development

Genetic studies in Disorders of Sex Development (DSD), representing a wide spectrum of developmental or functional conditions of the gonad, have mainly been oriented towards the coding genome. Application of genomic technologies, such as whole-exome sequencing, result in a molecular genetic diagnosis in ∼50% of cases with DSD. Many of the genes mutated in DSD encode transcription factors such as SRY, SOX9, NR5A1, and FOXL2, characterized by a strictly regulated spatiotemporal expression. Hence, it can be hypothesized that at least part of the missing genetic variation in DSD can be explained by non-coding mutations in regulatory elements that alter gene expression, either by reduced, mis- or overexpression of their target genes. In addition, structural variations such as translocations, deletions, duplications or inversions can affect the normal chromatin conformation by different mechanisms. Here, we review non-coding defects in human DSD phenotypes and in animal models. The wide variety of non-coding defects found in DSD emphasizes that the regulatory landscape of known and to be discovered DSD genes has to be taken into consideration when investigating the molecular pathogenesis of DSD.

Biology of the Sertoli Cell in the Fetal, Pubertal, and Adult Mammalian Testis

A healthy man typically produces between 50 × 10(6) and 200 × 10(6) spermatozoa per day by spermatogenesis; in the absence of Sertoli cells in the male gonad, this individual would be infertile. In the adult testis, Sertoli cells are sustentacular cells that support germ cell development by secreting proteins and other important biomolecules that are essential for germ cell survival and maturation, establishing the blood-testis barrier, and facilitating spermatozoa detachment at spermiation. In the fetal testis, on the other hand, pre-Sertoli cells form the testis cords, the future seminiferous tubules. However, the role of pre-Sertoli cells in this process is much less clear than the function of Sertoli cells in the adult testis. Within this framework, we provide an overview of the biology of the fetal, pubertal, and adult Sertoli cell, highlighting relevant cell biology studies that have expanded our understanding of mammalian spermatogenesis.

DSDs: genetics, underlying pathologies and psychosexual differentiation

Mammalian sex determination is the unique process whereby a single organ, the bipotential gonad, undergoes a developmental switch that promotes its differentiation into either a testis or an ovary. Disruptions of this complex genetic process during human development can manifest as disorders of sex development (DSDs). Sex development can be divided into two distinct processes: sex determination, in which the bipotential gonads form either testes or ovaries, and sex differentiation, in which the fully formed testes or ovaries secrete local and hormonal factors to drive differentiation of internal and external genitals, as well as extragonadal tissues such as the brain. DSDs can arise from a number of genetic lesions, which manifest as a spectrum of gonadal (gonadal dysgenesis to ovotestis) and genital (mild hypospadias or clitoromegaly to ambiguous genitalia) phenotypes. The physical attributes and medical implications associated with DSDs confront families of affected newborns with decisions, such as gender of rearing or genital surgery, and additional concerns, such as uncertainty over the child's psychosexual development and personal wishes later in life. In this Review, we discuss the underlying genetics of human sex determination and focus on emerging data, genetic classification of DSDs and other considerations that surround gender development and identity in individuals with DSDs.

Switching on sex: transcriptional regulation of the testis-determining gene Sry

Mammalian sex determination hinges on the development of ovaries or testes, with testis fate being triggered by the expression of the transcription factor sex-determining region Y (Sry). Reduced or delayed Sry expression impairs testis development, highlighting the importance of its accurate spatiotemporal regulation and implying a potential role for SRY dysregulation in human intersex disorders. Several epigenetic modifiers, transcription factors and kinases are implicated in regulating Sry transcription, but it remains unclear whether or how this farrago of factors acts co-ordinately. Here we review our current understanding of Sry regulation and provide a model that assembles all known regulators into three modules, each converging on a single transcription factor that binds to the Sry promoter. We also discuss potential future avenues for discovering the cis-elements and trans-factors required for Sry regulation.

Unique karyotype: mos 46,X,dic(X;Y)(p22.33;p11.32)/ 45,X/45,dic(X;Y)(p22.33;p11.32) in an Egyptian patient with Ovotesticular disorder of sexual development

Ovotesticular disorder of sexual development (OT-DSD) is an unusual form of DSD, characterized by the coexistence of testicular and ovarian tissue in the same individual. In this report, we present clinical, cytogenetic and molecular data of an Egyptian patient with ambiguous genitalia and OT-DSD, who had a unique karyotype comprising 3 different cell lines: mos 46,X,dic(X;Y)(p22.33;p11.32)/45,X/ 45,dic(X;Y)(p22.33;p11.32). This mosaic karyotype probably represents 2 different events: abnormal recombination between the X and Y chromosomes during paternal meiosis and postzygotic abnormality in mitotic segregation of the dic(X;Y) chromosome, resulting in a mosaic karyotype. The presence of the sex-determining region Y (SRY) gene explains the development of testicular tissue. On the other hand, other factors, including the presence of a 45,X cell line, partial SRY deletion, X inactivation pattern, and position effect, could be contributed to genital ambiguity. Explanation of the patient's phenotype in relation to the genotype is discussed with a literature review. We conclude that FISH analysis with X- and Y-specific probes and molecular analysis of the SRY gene are highly recommended and allow accurate diagnosis for optimal management of cases with ambiguous genitalia.

Understanding the genetic aetiology in patients with XY DSD

BACKGROUND

Disorders of sex development (DSD) consist of a wide range of disorders and are commoner in those with an XY karyotype. In over half of these cases who have a 46,XY karyotype and who are raised as boys, the underlying aetiology remains unclear.

AREAS OF AGREEMENT

Identification of the underlying genetic abnormality may predict long-term outcome. However, genetic abnormalities that are associated with XY DSD manifest themselves with a wide range of phenotype. To understand the aetiology as well as the phenotypic variation, there is a need to harness the advanced genetic technology that is now available.

AREAS OF CONTROVERSY

The point at which genetic analysis should be undertaken in the course of investigations is unclear. In addition, there is little agreement on the most effective approach for genetic analysis that will be of clinical benefit to the patient.

AREAS TIMELY FOR DEVELOPING RESEARCH

There is a need to understand and improve the clinical utility of genetic analysis in the clinical setting of the patient with a suspected DSD. This will be even more important when parallel gene sequencing identifies variations in multiple genes.

Gender Development in 46,XY DSD: Influences of Chromosomes, Hormones, and Interactions with Parents and Healthcare Professionals

Variables that impact gender development in humans are difficult to evaluate. This difficulty exists because it is not usually possible to tease apart biological influences on gender from social variables. People with disorders of sex development, or DSD, provide important opportunities to study gender within individuals for whom biologic components of sex can be discordant with social components of gender. While most studies of gender development in people with 46,XY DSD have historically emphasized the importance of genes and hormones on gender identity and gender role, more recent evidence for a significant role for socialization exists and is considered here. For example, the influence of parents' perceptions of, and reactions to, DSD are considered. Additionally, the impact of treatments for DSD such as receiving gonadal surgeries or genitoplasty to reduce genital ambiguity on the psychological development of people with 46,XY DSD is presented. Finally, the role of multi-disciplinary care including access to peer support for advancing medical, surgical and psychosexual outcomes of children and adults with 46,XY DSD, regardless of sex of rearing, is discussed.

A position effect on TRPS1 is associated with Ambras syndrome in humans and the Koala phenotype in mice

Ambras syndrome (AS) is a rare form of congenital hypertrichosis with excessive hair on the shoulders, face and ears. Cytogenetic studies have previously implicated an association with rearrangements of chromosome 8. Here we define an 11.5 Mb candidate interval for AS on chromosome 8q based on cytogenetic breakpoints in three patients. TRPS1, a gene within this interval, was deleted in a patient with an 8q23 chromosomal rearrangement, while its expression was significantly downregulated in another patient with an inversion breakpoint 7.3 Mb downstream of TRPS1. Here, we describe the first potential long-range position effect on the expression of TRPS1. To gain insight into the mechanisms by which Trps1 affects the hair follicle, we performed a detailed analysis of the hair abnormalities in Koa mice, a mouse model of hypertrichosis. We found that the proximal breakpoint of the Koa inversion is located 791 kb upstream of Trps1. Quantitative real-time polymerase chain reaction, in situ hybridization and immunofluorescence analysis revealed that Trps1 expression levels are reduced in Koa mutant mice at the sites of pathology for the phenotype. We determined that the Koa inversion creates a new Sp1 binding site and translocates additional Sp1 binding sites within a highly conserved stretch spanning the proximal breakpoint, providing a potential mechanism for the position effect. Collectively, these results describe a position effect that downregulates TRPS1 expression as the probable cause of hypertrichosis in AS in humans and the Koa phenotype in mice.

Rapid sex determination using PCR technique compared to classic cytogenetics

BACKGROUND

Fetal sexual differentiation relies on the translation of chromosomal sex established at fertilization into gonadal sex and somatic sex as development proceeds. In cases where chromosomal, gonadal, and somatic sex are incongruent in human infants and children, rapid establishment of the diagnosis and implementation of medical and surgical management is of paramount importance, since the gender identity is so important to the psychological well-being throughout life.

OBJECTIVE

This work was done in order to test the value of PCR technique for rapid sex determination compared to classic cytogenetic technique.

METHODS

Subjects included 20, cases including 10 neonates with ambiguous genitalia, 2 adult females with delayed puberty and 8 adult males with infertility, in addition to 20 normal infants of both sexes as a control group. The diagnosis of sex was attempted through examination, cytogenetic study, ultrasonography, gonadal biopsy and hormonal analysis, in addition to PCR amplification for the detection of SRY and ATL1 gene loci on Y and X chromosomes respectively.

RESULTS

Four neonates were diagnosed as partial testicular feminization showed both positive bands for the Y and X chromosomes and a karyogram of 46/XY. Three neonates were diagnosed as true hermaphrodites showed positive amplification for both Y and X chromosomes with a mosaic karyogram 46,XX/XY. Three neonates were diagnosed as cases of adrenogenital syndrome showed positive amplification of only the Xchromosome and had a karyogram of 46/XX. One of the two adult females was diagnosed as turner syndrome showed positive amplification of the X chromosome and a karyogram of 45/XO; the other one was diagnosed as complete testicular feminization had a positive amplification of X and Y chromosomes and a karyogram of 46/XY. The 8 adult males with infertility showed a positive amplification of X and Y chromosome and a karyogram of 47/XXY (Klinefelter syndrome) in 7 cases and 46/XY gonadal dysgenesis in one case.

CONCLUSION

We concluded that PCR as a simple, rapid and reliable technique can complement and also confirm cytogenetic studies in the diagnosis of sex in cases of sex chromosome disorders.

Primary amenorrhea in a 46,XY adolescent girl with partial gonadal dysgenesis: identification of a new SRY gene mutation

OBJECTIVE

To determine the genetic cause of primary amenorrhea in a 46,XY adolescent girl.

DESIGN

Case report.

SETTING

Pediatric endocrinology and gynecologic unit of an academic hospital.

PATIENT(S)

A 16-year-old adolescent referred for primary amenorrhea.

INTERVENTION(S)

Endocrine and surgical investigation, SRY mutational analysis.

MAIN OUTCOME MEASURE(S)

Plasma gonadotropin levels, estradiol and testosterone levels, and pathologic findings.

RESULT(S)

We report a new mutation of the SRY gene in a 46,XY sex-reversed patient. We observed two unusual features. First, partial pubertal development has rarely been described in association with SRY gene mutation. Second, the location of the mutation was in the HMG box region of the SRY gene, in contrast to the other partial cases of 46,XY gonadal dysgenesis. In addition, the presence of a gonadoblastoma underlines the necessity of removing the gonads quickly in 46,XY sex-reversal cases, and raises several questions about the role of the SRY gene in the development of such tumors.

CONCLUSION(S)

Partial pubertal development in a 46,XY sex-reversed patient does not exclude SRY gene mutation.

Mechanisms of disease: Transcription factors in sex determination--relevance to human disorders of sex development

Sex determination is the series of molecular events that direct the undifferentiated bipotential gonad to become either a testis or an ovary. In humans, disruption of this process results in intersexuality, also referred to as disorders of sex development (DSD). Despite the discovery of the sex-determining gene SRY (sex-determining region Y) 15 years ago, the molecular mechanisms of sex determination remain poorly understood. Analysis of clinically relevant mutations of sex-determining genes in individuals with DSD has provided considerable insight into the function of these genes. The majority of disorders of sex determination with known causes are explained by mutations in one of three transcription factors at the core of the sex-determining pathway: SRY, SOX9 (SRY-box 9) and NR5A1 (nuclear receptor subfamily 5, group A, member 1). These mutations either affect the level of protein available at its nuclear site of action (via changes in regulatory sequences, deletions, non-sense mutations or mutations in nuclear localization sequences), or alter the structure of the protein (via modifications of binding or bending activity, or of interactions with other proteins). Deciphering the functional diversity of the mutations affecting the sex-determining pathway has immediate clinical impact on the diagnosis, outcome studies and classification of patients with DSD.

Structural variants: changing the landscape of chromosomes and design of disease studies

The near completeness of human chromosome sequences is facilitating accurate characterization and assessment of all classes of genomic variation. Particularly, using the DNA reference sequence as a guide, genome scanning technologies, such as microarray-based comparative genomic hybridization (array CGH) and genome-wide single nucleotide polymorphism (SNP) platforms, have now enabled the detection of a previously unrecognized degree of larger-sized (non-SNP) variability in all genomes. This heterogeneity can include copy number variations (CNVs), inversions, insertions, deletions and other complex rearrangements, most of which are not detected by standard cytogenetics or DNA sequencing. Although these genomic alterations (collectively termed structural variants or polymorphisms) have been described previously, mainly through locus-specific studies, they are now known to be more global in occurrence. Moreover, as just one example, CNVs can contain entire genes and their number can correlate with the level of gene expression. It is also plausible that structural variants may commonly influence nearby genes through chromosomal positional or domain effects. Here, we discuss what is known of the prevalence of structural variants in the human genome and how they might influence phenotype, including the continuum of etiologic events underlying monogenic to complex diseases. Particularly, we highlight the newest studies and some classic examples of how structural variants might have adverse genetic consequences. We also discuss why analysis of structural variants should become a vital step in any genetic study going forward. All these progresses have set the stage for a golden era of combined microscopic and sub-microscopic (cytogenomic)-based research of chromosomes leading to a more complete understanding of the human genome.

Holoprosencephaly and cleidocranial dysplasia in a patient due to two position-effect mutations: case report and review of the literature

Holoprosencephaly (HPE) is a genetically heterogeneous developmental field defect in which midline cleavage of the forebrain and craniofacial structures is impaired. Based on the analysis of HPE patients with chromosome rearrangements, at least six loci for the disorder have been assigned. The sonic hedgehog gene (SHH) at 7q36 has been identified as the HPE3 locus. Cleidocranial dysplasia (CCD) is an autosomal dominant skeletal disorder characterized by clavicular, pelvic and dental anomalies. It is caused by mutations in the osteoblast-specific transcription factor CBFA1/RUNX2, which maps to 6p21. We report a 20-year-old female with premaxillary agenesis (part of the HPE spectrum), as well as skeletal abnormalities and impacted teeth reminiscent of CCD. She carries a de novo 6;7 reciprocal translocation, with breakpoints at 6p21.1 and 7q36. We have shown previously that the 7q36 breakpoint maps 15 kb telomeric to the 5' end of SHH, which explains the patient's HPE phenotype. Now, using fluorescence in situ hybridization, we have identified a P1 artificial chromosome clone 800 kb upstream of CBFA1/RUNX2 that spans the 6p breakpoint. We propose that the proband's complex phenotype is due to two position-effect (PE) mutations, one at each translocation breakpoint, which have altered the expression of the SHH and CBFA1/RUNX2 genes. The role of PE mutations in human disease is also reviewed.

Mutations in SRY and WT1 genes required for gonadal development are not responsible for XY partial gonadal dysgenesis

The WT1 transcription factor regulates SRY expression during the initial steps of the sex determination process in humans, activating a gene cascade leading to testis differentiation. In addition to causing Wilms' tumor, mutations in WT1 are often responsible for urogenital defects in men, while SRY mutations are mainly related to 46,XY pure gonadal dysgenesis. In order to evaluate their role in abnormal testicular organogenesis, we screened for SRY and WT1 gene mutations in 10 children with XY partial gonadal dysgenesis, 2 of whom with a history of Wilms' tumor. The open reading frame and 360 bp of the 5' flanking sequence of the SRY gene, and the ten exons and intron boundaries of the WT1 gene were amplified by PCR of genomic DNA. Single-strand conformation polymorphism was initially used for WT1 mutation screening. Since shifts in fragment migration were only observed for intron/exon 4, the ten WT1 exons from all patients were sequenced manually. No mutations were detected in the SRY 5' untranslated region or within SRY open-reading frame sequences. WT1 sequencing revealed one missense mutation (D396N) in the ninth exon of a patient who also had Wilms' tumor. In addition, two silent point mutations were found in the first exon including one described here for the first time. Some non-coding sequence variations were detected, representing one new (IVS4+85A>G) and two already described (-7ATG T>G, IVS9-49 T>C) single nucleotide polymorphisms. Therefore, mutations in two major genes required for gonadal development, SRY and WT1, are not responsible for XY partial gonadal dysgenesis.

Fetal hormones and sexual differentiation

The process of fetal sexual differentiation, which involves establishment of genetic sex, differentiation of the gonads, and development of phenotypic sex, is summarized. The morphologic changes that occur in utero that lead to development of the male and female gonads, germ cells, reproductive tracts, and external genitalia are described. Most of the article focuses on the hormones that regulate sexual differentiation and development in utero. The genetic factors that regulate sexual differentiation, which constitute a new and emerging field, also are discussed.

Fishing for new genes in skin biology: impact of cytogenetics on gene discovery

Research into the field of skin biology has grown exponentially over the past two decades. Even though the fundamental molecular pathways are still not fully understood, there have been significant advances in our understanding of the underlying mechanisms involved in the pathogenesis of genodermatosis. The cloning of many candidate genes involved in the etiology of skin diseases has been facilitated by initial cytogenetic evidence. This review will synthesize recent findings that led to the discovery of candidate genes for anhidrotic ectodermal dysplasia, Williams-Beuren syndrome, neurofibromatosis-I and tricho-rhino-phalangeal syndrome.

Screening for mutations in the SRY gene in patients with mixed gonadal dysgenesis or with Turner syndrome and Y mosaicism

OBJECTIVE

To investigate the presence of mutations in the open reading frame (ORF), as well as on the 5' and 3', flanking regions of the SRY gene in patients with mixed gonadal dysgenesis (MGD) or with Turner syndrome (TS) and Y mosaicism.

STUDY DESIGN

We studied 13 patients with MGD and three patients with TS and Y mosaicism. DNA was isolated from blood leukocytes for subsequent polymerase chain reaction (PCR) and direct sequencing were performed in the ORF, as well as from the 5' and 3' flanking regions of the SRY gene.

RESULTS

No mutations were present in any of the patients studied.

CONCLUSION

The absence of mutations in these regions indicated that mutations were an unlikely cause of MGD or TS with Y mosaicism and suggested that there are others genes playing an important role in sex development.

Turning on the male – SRY, SOX9 and sex determination in mammals

The decision of the bi-potential gonad to develop into either a testis or ovary is determined by the presence or absence of the Sex-determining Region gene on the Y chromosome (SRY). Since its discovery, almost 13 years ago, the molecular role that SRY plays in initiating the male sexual development cascade has proven difficult to ascertain. While biochemical studies of clinical mutants and mouse genetic models have helped in our understanding of SRY function, no direct downstream targets of SRY have yet been identified. There are, however, a number of other genes of equal importance in determining sexual phenotype, expressed before and after expression of SRY. Of these, one has proven of central importance to mammals and vertebrates, SOX9. This review describes our current knowledge of SRY and SOX9 structure and function in the light of recent key developments.

The molecular action and regulation of the testis-determining factors, SRY (sex-determining region on the Y chromosome) and SOX9 [SRY-related high-mobility group (HMG) box 9]

Despite 12 yr since the discovery of SRY, little is known at the molecular level about how SRY and the SRY-related protein, SOX9 [SRY-related high-mobility group (HMG) box 9], initiate the program of gene expression required to commit the bipotential embryonic gonad to develop into a testis rather than an ovary. Analysis of SRY and SOX9 clinical mutant proteins and XX mice transgenic for testis-determining genes have provided some insight into their normal functions. SRY and SOX9 contain an HMG domain, a DNA-binding motif. The HMG domain plays a central role, being highly conserved between species and the site of nearly all missense mutations causing XY gonadal dysgenesis. SRY and SOX9 are architectural transcription factors; their HMG domain is capable of directing nuclear import and DNA bending. Whether SRY and SOX9 activate testis-forming genes, repress ovary-forming genes, or both remains speculative until downstream DNA target genes are identified. However, factors that control SRY and SOX9 gene expression have been identified, as have a dozen sex-determining genes, allowing some of the pieces in this molecular genetic puzzle to be connected. Many genes, however, remain unidentified, because in the majority of cases of XY females and in all cases of XX males lacking SRY, the mutated gene is unknown.

Transcription factor SOX3 is involved in X-linked mental retardation with growth hormone deficiency

Physical mapping of the breakpoints of a pericentric inversion of the X chromosome (46,X,inv[X][p21q27]) in a female patient with mild mental retardation revealed localization of the Xp breakpoint in the IL1RAPL gene at Xp21.3 and the Xq breakpoint near the SOX3 gene (SRY [sex determining region Y]-box 3) (GenBank accession number NM_005634) at Xq26.3. Because carrier females with microdeletion in the IL1RAPL gene do not present any abnormal phenotype, we focused on the Xq breakpoint. However, we were unable to confirm the involvement of SOX3 in the mental retardation in this female patient. To validate SOX3 as an X-linked mental retardation (XLMR) gene, we performed mutation analyses in families with XLMR whose causative gene mapped to Xq26-q27. We show here that the SOX3 gene is involved in a large family in which affected individuals have mental retardation and growth hormone deficiency. The mutation results in an in-frame duplication of 33 bp encoding for 11 alanines in a polyalanine tract of the SOX3 gene. The expression pattern during neural and pituitary development suggests that dysfunction of the SOX3 protein caused by the polyalanine expansion might disturb transcription pathways and the regulation of genes involved in cellular processes and functions required for cognitive and pituitary development.

Equilibrium binding assays reveal the elevated stoichiometry and salt dependence of the interaction between full-length human sex-determining region on the Y chromosome (SRY) and DNA

In an effort to better define the molecular mechanism of the functional specificity of human sex-determining region on the Y chromosome (SRY), we have carried out equilibrium binding assays to study the interaction of the full-length bacterial-expressed protein with a DNA response element derived from the CD3epsilon gene enhancer. These assays are based on the observation of the fluorescence anisotropy of a fluorescein moiety covalently bound to the target oligonucleotide. The low anisotropy value due to the fast tumbling of the free oligonucleotide in solution increases substantially upon binding the protein to the labeled target DNA. Our results indicate that the full-length human wild-type SRY (SRY(WT)) forms a complex of high stoichiometry with its target DNA. Moreover, we have demonstrated a strong salt dependence of both the affinity and specificity of the interaction. We have also addressed the DNA bending properties of full-length human SRY(WT) in solution by fluorescence resonance energy transfer and revealed that maximal bending is achieved with a protein to DNA ratio significantly higher than the classical 1:1. Oligomerization thus appears, at least in vitro, to be tightly coupled to SRY-DNA interactions. Alteration of protein-protein interactions observed for the mutant protein SRY(Y129N), identified in a patient presenting with 46,XY sex reversal, suggests that oligomerization may play an important role in vivo as well.

The genetics of male undermasculinization

A review of the genetics of male undermasculinization must encompass a description of the embryology of the genital system. The dimorphism of sex development consequent upon the formation of a testis and the subsequent secretion of hormones to impose a male phenotype is highlighted. Thus, an understanding of the causes of male undermasculinization (manifest as XY sex reversal, complete and partial) includes reviewing the genetic factors which control testis determination and the production and action of testicular hormones. The study of disorders of male sex development has contributed substantially to knowledge of normal male development before birth. This knowledge has been complimented in recent years by the use of targeted murine gene disruption experiments to study the sex phenotype, although murine and human phenotypes are not always concordant. The investigation of disorders associated with male undermasculinization of prenatal onset is described briefly to complete the review.

Molecular analysis of SRY gene in patients with mixed gonadal dysgenesis

Mixed gonadal dysgenesis (MGD) includes a group of heterogeneous conditions consisting of a dysgenetic testis with a streak gonad. MGD is probably due to a disturbance in testicular determination/differentiation. The objective of this study is to analyze the SRY gene in MGD patients. A molecular investigation was undertaken in sixteen patients with this disorder in an attempt to determine mutations in SRY through polymerase chain reaction, single strand conformational polymorphism and direct sequencing. Eleven patients showed 45,X/46,XY and five 46,XY karyotype. Mutations in SRY gene were shown to be absent in these patients. This study confirms the findings of other studies. The etiology of MGD is heterogeneous, and cytogenetics mosaicism typically seen in these patients may be a cause of this condition, although, the presence of mutations in testicular organizing genes downstream of SRY is still to rule out.

Testis determination in mammals: more questions than answers

In humans, testis development depends on a regulated genetic hierarchy initiated by the Y-linked SRY gene. Failure of testicular determination results in the condition termed 46,XY gonadal dysgenesis (GD). Several components of the testis determining pathway have recently been identified though it has been difficult to articulate a cascade with the known elements of the system. It seems, however, that early gonadal development is the result of a network of interactions instead of the outcome of a linear cascade. Accumulating evidence shows that testis formation in man is sensitive to gene dosage. Haploinsufficiency of SF1, WT1 and SOX9 is responsible for 46,XY gonadal dysgenesis. Besides, data on SRY is consistent with possible dosage anomalies in certain cases of male to female sex reversal. 46,XY GD due to monosomy of distal 9p and 10q might also be associated with an insufficient gene dosage effect. Duplications of the locus DSS can lead to a failure of testicular development and a duplication of the region containing SOX9 has been implicated in XX sex reversal. Transgenic studies in mouse have shown, however, that this mammal is less sensitive to gene dosage than man. Here, we will try to put in place the known pieces of the jigsaw puzzle that is sex determination in mammals, as far as current knowledge obtained from man and animal models allows. We are certain that from this attempt more questions than answers will arise.

Sry, Sox9 and mammalian sex determination

Sry is the Y-chromosomal gene that acts as a trigger for male development in mammalian embryos. This gene encodes a high mobility group (HMG) box transcription factor that is known to bind to specific target sequences in DNA and to cause a bend in the chromatin. DNA bending appears to be part of the mechanism by which Sry influences transcription of genes downstream in a cascade of gene regulation leading to maleness, but the factors that cooperate with, and the direct targets of, Sry remain to be identified. One gene known to be downstream from Sry in this cascade in Sox9, which encodes a transcription factor related to Sry by the HMG box. Like Sry, mutations in Sox9 disrupt male development, but unlike Sry, the role of Sox9 is not limited to mammals. This review focuses on what is known about the two genes and their likely modes of action, and draws together recent data relating to how they might interconnect with the network of gene activity implicated in testis determination in mammals.

Three novel SRY mutations in XY gonadal dysgenesis and the enigma of XY gonadal dysgenesis cases without SRY mutations

Mutations in the Y-located testis-determining gene SRY are one cause for XY sex reversal. We have previously identified four SRY mutations in a total of 45 sex-reversed females with XY gonadal dysgenesis (XY GD). In a new sample of 16 XY GD cases, three previously undescribed SRY mutations were identified. Two are point mutations that lead to amino acid substitutions in the HMG domain of SRY, M64R, and F67V. The third SRY mutation is a single base insertion 5' to the HMG box within codon 43, converting this lysine codon to a stop codon (K43X). A total of 33 SRY mutations have so far been described that account for only 10-15% of XY GD females. A further 10-15% of these cases result from deletion of SRY due to aberrant X/Y interchange. The etiology of the remaining 70-80% of XY GD cases is still enigmatic. Possible explanations for these XY sex-reversal cases are discussed.

Sex determination and the Y chromosome

Although SRY was first identified 10 years ago, we still know remarkably little about its mode of action or downstream target genes. Recently, potential protein partners have been identified and there has been considerable activity to understand the roles of WT1, SF-1, DAX-1 and SOX9 in gonadogenesis. The emerging picture is one of complex interactions, involving both positive and negative regulatory signals that, depending on the cellular and promoter context, drive the expression of male-specific genes. Despite recent advances, however, we are still unable to explain the genetic cause of most cases of 46,XY gonadal dysgenesis or even a single case of Y-chromosome-negative 46,XX maleness.

Prenatal karyotype and ultrasound discordance in intersex conditions

An infant born at 38 weeks' gestation with ambiguous genitalia had a prenatal 45X karyotype but an enlarged phallus on an ultrasound scan at 31 weeks' gestation. The newborn examination demonstrated penoscrotal hypospadias with chordee and two gonads palpable in the scrotum with a right hydrocele. Ultrasound showed a saccular structure containing debris behind the bladder. The postnatal karyotype was revealed to be 45X/46XY, with a pseudodicentric Y chromosome. Cystoscopy/genitography identified a uterus and a right fallopian tube, which were removed along with a dysgenetic right gonad. Biopsy of the descended left gonad revealed rare germ cells. The final diagnosis was 45X/46XY male pseudohermaphroditism with testicular dysgenesis. One should be aware of possible chromosomal mosaicism and combine the prenatal karyotype with the ultrasound genital findings to formulate an intersex differential diagnosis.

Variants of the type II 3beta-hydroxysteroid dehydrogenase gene in children with premature pubic hair and hyperandrogenic adolescents

To ascertain the potential role of heterozygosity for 3beta-hydroxysteroid (3beta-HSD) deficiency in children with premature pubic hair and adolescent girls with hyperandrogenism, we performed single-strand conformational polymorphism (SSCP) analysis of the 3beta-hydroxysteroid dehydrogenase type 2 (3beta-HSD2) gene in 34 hyperandrogenic patients. Three sequence variants, two missense mutations and a 3'-UTR sequence variant, were detected among seven patients and in none of 100 healthy control subjects. One of these seven patients carried Leu236 --> Ser on one 3beta-HSD2 allele and Glu318 --> STOP on one 21-hydroxylase (CYP21) allele. ACTH stimulation tests were performed in 5/7 patients with sequence variants and were compatible with decreased 3beta-hydroxysteroid dehydrogenase activity in three. Thus, 7 of 34 (20.6%) mildly hyperandrogenic patients carry heterozygous sequence variants of the 3beta-HSD2 gene. Since obligate heterozygotic carriers for congenital adrenal hyperplasia are typically asymptomatic, other genetic or environmental influences may contribute to the expression of hyperandrogenic symptoms in our patients.

Sex in the 90s: SRY and the switch to the male pathway

In mammals the male sex determination switch is controlled by a single gene on the Y chromosome, SRY. SRY encodes a protein with an HMG-like DNA-binding domain, which probably acts as a local organizer of chromatin structure. It is believed to regulate downstream genes in the sex determination cascade, although no direct targets of SRY are clearly known. More genes in the pathway have been isolated through mutation approaches in mouse and human. At least three genes, SRY itself, SOX9, and DAX1, are dosage sensitive, providing molecular evidence that the sex determination step operates at a critical threshold. SRY initiates development of a testis from the bipotential cells of the early gonad. The dimorphic male and female pathways present a rare opportunity to link a pivotal gene in development with morphogenetic mechanisms that operate to pattern an organ and the differentiation of its cells. Mechanisms of testis organogenesis triggered downstream of SRY include pathways of cell signaling controlling cell reorganization, cell proliferation, cell migration, and vascularization.