Sex-determining Gene SRY Research Articles

Review: Sex Chromosome Evolution and the Expression of Sex-Specific Genes in the Placenta

Sex chromosomes have a disproportionate influence on health and disease. Both the X and Y are atypical in gene content and activity, as a result of their unique evolutionary trajectory. The X and Y chromosomes originated in a pair of autosomes, and differentiated as the Y chromosome degenerated progressively. The Y contains few active genes and is composed largely of repetitive DNA sequences. Most Y genes have copies on the X from which they evolved; this includes even the sex-determining gene SRY as well as several genes required for spermatogenesis. The X contains a disproportionate number of genes that affect reproduction and brain function (or both). It is also subject to inactivation in females, so that females are mosaics composed of patches of tissue that express only the genes on either the maternally or the paternally derived X chromosome. Several widely expressed genes on the Y chromosome code for male-specific proteins that provoke an immune reaction in females; this HY antigen has a measurable effect on maternal-fetal incompatibility. Imprinted paternal X inactivation in rodent extraembryonic tissues would be expected to mitigate the effect of foreign paternal antigens; however, paternal inactivation seems not to occur in the human placenta.

The male-determining gene SRY is a hybrid of DGCR8 and SOX3, and is regulated by the transcription factor CP2

In mammals, sex is determined by the presence or absence of the Y chromosome that bears a male-dominant sex-determining gene SRY, which switches the differentiation of gonads into male testes. The molecular signaling mechanism turning on the switch, however, has remained unclear for 18 years since the identification of the gene. Here, we describe how this gene emerged and started to work. From amino acid homology, we realized that SRY is a hybrid gene between a portion of the first exon of DiGeorge syndrome critical region gene 8 (DGCR8) and the high-mobility group (HMG) box of SRY box-3 (SOX3) gene. We identified the regulatory sequence in the SRY promotor region by searching for a common motif shared with DGCR8 mRNA. From the motif search between DGCR8 mRNA and the SRY upstream sequence, we found that the transcription factor CP2 (TFCP2) binding motif is present in both. TFCP2 overexpression did not show a significant increase of SRY mRNA expression, and TFCP2 suppression by RNA interference (RNAi) significantly reduced SRY mRNA expression. Furthermore, electrophoretic mobility shift assay (EMSA) demonstrated that TFCP2 acts as a regulator by directly binding to the SRY promoter. We conclude that SRY is a hybrid gene composed of two genes, DGCR8 and SOX3; and TFCP2 is an essential transcription factor for SRY expression regulation.

Re‐sequencing regions of the ovine Y chromosome in domestic and wild sheep reveals novel paternal haplotypes

The male-specific region of the ovine Y chromosome (MSY) remains poorly characterized, yet sequence variants from this region have the potential to reveal the wild progenitor of domestic sheep or examples of domestic and wild paternal introgression. The 5' promoter region of the sex-determining gene SRY was re-sequenced using a subset of wild sheep including bighorn (Ovis canadensis), thinhorn (Ovis dalli spp.), urial (Ovis vignei), argali (Ovis ammon), mouflon (Ovis musimon) and domestic sheep (Ovis aries). Seven novel SNPs (oY2-oY8) were revealed; these were polymorphic between but not within species. Re-sequencing and fragment analysis was applied to the MSY microsatellite SRYM18. It contains a complex compound repeat structure and sequencing of three novel size fragments revealed that a pentanucleotide element remained fixed, whilst a dinucleotide element displayed variability within species. Comparison of the sequence between species revealed that urial and argali sheep grouped more closely to the mouflon and domestic breeds than the pachyceriforms (bighorn and thinhorn). SNP and microsatellite data were combined to define six previously undetected haplotypes. Analysis revealed the mouflon as the only species to share a haplotype with domestic sheep, consistent with its status as a feral domesticate that has undergone male-mediated exchange with domestic animals. A comparison of the remaining wild species and domestic sheep revealed that O. aries is free from signatures of wild sheep introgression.

Weird Animal Genomes and the Evolution of Vertebrate Sex and Sex Chromosomes

Humans, mice, and even kangaroos have an XX female:XY male system of sex determination, in which the Y harbors a male-dominant sex-determining gene SRY. Birds have the opposite, ZZ males and ZW females, and may use a dosage-sensitive Z-borne gene. Other reptiles have genetic sex but no visible sex chromosomes, or determine sex by temperature of egg incubation. How can we make sense of so much variation? How do systems change in evolution? Studies of some unlikely animals-platypus and dragon lizards, frogs and fish-confirm that evolutionary transitions have occurred between TSD and GSD systems, between XY and ZW systems, and even between male and female heterogametic systems. Here I explore nonmodel systems that offer some new perspectives on some venerable questions of sex and sex chromosomes.

Mammalian sex—Origin and evolution of the Y chromosome and SRY

Sex determination in vertebrates is accomplished through a highly conserved genetic pathway. But surprisingly, the downstream events may be activated by a variety of triggers, including sex determining genes and environmental cues. Amongst species with genetic sex determination, the sex determining gene is anything but conserved, and the chromosomes that bear this master switch subscribe to special rules of evolution and function. In mammals, with a few notable exceptions, female are homogametic (XX) and males have a single X and a small, heterochromatic and gene poor Y that bears a male dominant sex determining gene SRY. The bird sex chromosome system is the converse in that females are the heterogametic sex (ZW) and males the homogametic sex (ZZ). There is no SRY in birds, and the dosage-sensitive Z-borne DMRT1 gene is a credible candidate sex determining gene. Different sex determining switches seem therefore to have evolved independently in different lineages, although the complex sex chromosomes of the platypus offer us tantalizing clues that the mammal XY system may have evolved directly from an ancient reptile ZW system. In this review we will discuss the organization and evolution of the sex chromosomes across a broad range of mammals, and speculate on how the Y chromosome, and SRY, evolved.

The fate of donor bone cells in different diameter bone grafts: an experiment study

To investigate the fate of donor bone cells in bone grafts of different diameters during repairing bone defects. One hundred sixteen female syngeneic inbred DA rats were established as radial defect model of 3 kinds: structural bone grafting group (n = 56), morselized bone grafting group (n = 56), and blank group (without bone grafting, n = 4), to be used as receptors The ilia of 58 male inbred DA rats, as donors, were harvested and made into structural bone grafts 2 mm in diameter and morselized bone grafts 0.3 - 0.5 mm in diameter to be transplanted into the radial defects of the female receptors. One and four days, and 1, 2, 4, 6, and 8 weeks after transplantation DNA was extracted from the grafted bones and polymerase chain reaction (PCR) specific for the sex-determining region of Y-chromosome (Sry) was performed to observe the presence and relative amount of Y-chromosome originating from the bone grafts, expression of the sex-determining gene Sry in the receptors' bones and the histology of the receptors' bones. In structural bone grafting group, the amounts of Sry-specific bands decreased in the early time and disappeared 1 week after transplantation, and re-appeared 4 weeks after transplantation with the amount increasing with the lapse of time. In morselized bone grafting group, Sry-specific bands were detected all the time but their amounts decreased with the lapse of time. At each time point, morselized bone graft provided more living osteocytes with better effect of osteogenesis in comparison with the structural bone graft. Bone grafts of different diameters provide donor cells in repairing bone defects. Having more surviving osteocytes, morselized bone grafts may accelerate the healing pf bone defects, thus providing a new and effective method to repair bone defects and spinal fusion clinically.

Functional analysis of Sox8 and Sox9 during sex determination in the mouse.

Sex determination in mammals directs an initially bipotential gonad to differentiate into either a testis or an ovary. This decision is triggered by the expression of the sex-determining gene Sry, which leads to the activation of male-specific genes including the HMG-box containing gene Sox9. From transgenic studies in mice it is clear that Sox9 is sufficient to induce testis formation. However, there is no direct confirmation for an essential role for Sox9 in testis determination. The studies presented here are the first experimental proof for an essential role for Sox9 in mediating a switch from the ovarian pathway to the testicular pathway. Using conditional gene targeting, we show that homozygous deletion of Sox9 in XY gonads interferes with sex cord development and the activation of the male-specific markers Mis and P450scc, and leads to the expression of the female-specific markers Bmp2 and follistatin. Moreover, using a tissue specific knock-out approach, we show that Sox9 is involved in Sertoli cell differentiation, the activation of Mis and Sox8, and the inactivation of Sry. Finally, double knock-out analyses suggest that Sox8 reinforces Sox9 function in testis differentiation of mice.

A selective tropism of transfused oval cells for liver.

To explore the biological behaviors of hepatic oval cells after transfused into the circulation of experimental animals. Oval cells from male SD rat were transfused into the circulation of a female rat which were treated by a 2-AAF/CCl(4) program, through caudal vein. Sex-determining gene sry which located on Y chromosome was examined by PCR and in situ hybridization technique in liver, kidney and spleen of the experimental animals, respectively. The results of the cell-transplant experiment showed that the sry gene was detectable only in the liver but not in spleen and kidney of the experimental rats, and no signals could be detected in the control animals. It can be also morphologically proved that some exogenous cells had migrated into the parenchyma of the liver and settled there. The result means that there are exogenous cells located in the liver of the experimental animal and the localization is specific to the liver. This indicates that some "signal molecules" must exist in the circulation of the rats treated by 2-AAF/CCl(4). These "signal molecules" might play an important role in specific localization and differentiation of transfused oval cells.

The sex determining gene of medaka: a Y-specific DM domain gene (DMY) is required for male development

Although the sex-determining gene Sry has been identified in mammals, no comparable genes have been found in non-mammalian vertebrates. To clone positionally the sex-determining region of the medaka, Oryzias latipes, we generated a Y congenic strain to highlight the genetic differences between the X and Y chromosomes from inbred strains of medaka. We used recombinant breakpoint analysis and deletion analysis of the Y chromosome of a congenic XY female to restrict the sex-determining region to 250-kb stretch of the Y chromosome. Shotgun sequencing of this region predicted 27 genes. Three of these genes were expressed during sexual differentiation. However, only one gene was Y specific. The full-length cDNA sequence of this gene encodes a putative protein of 267 amino acids, including the highly conserved DM domain. We thus named it DMY. To establish a role for DMY during sexual differentiation, we screened wild medaka populations for naturally occurring DMY mutants. Two XY females with distinct mutations in DMY were found in separate populations. The first heritable mutant – a single insertion in exon 3 and the subsequent truncation of DMY – resulted in all XY female offspring. Similarly, the second XY mutant female showed reduced DMY expression with a high proportion of XY female offspring. Furthermore, during normal development, DMY is expressed only in somatic cells of XY gonads. These findings strongly suggest that the sex-specific DMY is required for normal testicular development and is a prime candidate for the medaka sex-determining gene.

Detection of multiple loci in single cell by primer extension preamplification and nest PCR

OBJECTIVE: To investigate the feasibility of multiple loci detection in single cell by primer extension preamplification (PEP) followed by nest PCR. METHODS: Using PEP, the whole genomic DNA in single lymphocyte or single blastomere was amplified. In addition, CD17, nt-28 and linked ATTTT repeat for beta-thalassemia, F508 and linked GATT repeat for cystic fibrosis, DMD exon 17 and 48 for Duchenne muscular dystrophy, short tandem repeats of D18S51, D21S11 and D21S1411, and sex-determination gene SRY of the Y chromosome were all detected using nest-PCR from a small aliquot of the PEP reaction. RESULTS: The rate of successful single lymphocyte amplification was 89.5%(false positive 0.48%false negative 2.5%). The rate of successful single blastomere amplification was 85.56%(false positive 3%). CONCLUSION: The PEP technique followed by nest PCR analysis of single cell is very useful for simultaneous detection of multiple gene loci. It may be applicable for preimplantation genetic diagnosis.

DMY is a Y-specific DM-domain gene required for male development in the medaka fish.

Although the sex-determining gene Sry has been identified in mammals, no comparable genes have been found in non-mammalian vertebrates. Here, we used recombinant breakpoint analysis to restrict the sex-determining region in medaka fish (Oryzias latipes) to a 530-kilobase (kb) stretch of the Y chromosome. Deletion analysis of the Y chromosome of a congenic XY female further shortened the region to 250 kb. Shotgun sequencing of this region predicted 27 genes. Three of these genes were expressed during sexual differentiation. However, only the DM-related PG17 was Y specific; we thus named it DMY. Two naturally occurring mutations establish DMY's critical role in male development. The first heritable mutant--a single insertion in exon 3 and the subsequent truncation of DMY--resulted in all XY female offspring. Similarly, the second XY mutant female showed reduced DMY expression with a high proportion of XY female offspring. During normal development, DMY is expressed only in somatic cells of XY gonads. These findings strongly suggest that the sex-specific DMY is required for testicular development and is a prime candidate for the medaka sex-determining gene.

Matrix metalloproteinases regulate mesonephric cell migration in developing XY gonads which correlates with the inhibition of tissue inhibitor of metalloproteinase-3 by Sry.

In the mouse, the sex determining gene Sry, on the Y chromosome, controls testis differentiation during embryogenesis. Following Sry expression, indifferent XY gonads increase their size relative to XX gonads and form cord-like structures with the adjacent mesonephros, providing XY gonad somatic cells. This mesonephric cell migration is known to depend on Sry, but the molecular mechanism of mesonephric cell migration remains unknown. In this study, it was shown that cells expressing Sry induced proliferation of mesonephric cells migrating into male gonads, and inhibited expression of the tissue inhibitor of metalloproteinases (TIMP)-3 gene, which is the endogenous inhibitor of matrix metalloproteinases (MMP). In addition, the mesonephric cell migration was blocked by a chemically synthesized inhibitor of MMP in a gonad/mesonephros organ co-culture system with enhanced green fluorescent protein transgenic embryos. The findings indicate that MMP may play a critical role in mesonephric cell migration, and the function of MMP may be regulated by a Sry-TIMP-3 cascade. These findings are an important clue for the elucidation of testicular formation in developing gonads.

Cloning and mapping of platypus SOX2 and SOX14: Insights into SOX group B evolution

Group B SOX genes, the closest relatives to the sex-determining gene SRY, are thought to have evolved from a single ancestral SOX B by a series of duplications and translocations. The two SOX B genes SOX2 and SOX14 co-localize to chromosome 3q in humans. SOX2 and SOX14 homologues were cloned and characterized in the platypus, a monotreme mammal distantly related to man. The two genes were found to co-localize to chromosome 1q in this species. Proximity of the two related genes has therefore been conserved for 170 Myr, since humans and platypus diverged. The sequence similarity and conserved synteny of these group B genes provide clues to their origin. A simple model of SOX group B gene evolution is proposed.

Sox9 induces testis development in XX transgenic mice.

Mutations in SOX9 are associated with male-to-female sex reversal in humans. To analyze Sox9 function during sex determination, we ectopically expressed this gene in XX gonads. Here, we show that Sox9 is sufficient to induce testis formation in mice, indicating that it can substitute for the sex-determining gene Sry.

The Human Sex-determining Gene SRY Is a Direct Target of WT1

The product of the Wilms' tumor gene, WT1, is essential for male sex determination and differentiation in mammals. In addition to causing Wilms' tumor, mutations in WT1 often cause two distinct but overlapping urogenital defects in men, Denys-Drash syndrome and Frasier syndrome. In this study we investigated the regulation of the sex determination gene SRY by WT1. Our results showed that WT1 up-regulates the SRY gene through the proximal early growth response gene-1-like DNA-binding sequences in the core promoter. Mutant WT1 proteins in Denys-Drash syndrome patients were unable to activate this promoter. These mutants did not act in a dominant negative manner, as expected over the wild-type WT1 in this promoter. We also found that WT1 could transactivate the endogenous SRY gene. These observations, together with the overlapping expression patterns of WT1 and SRY in human gonads, led us to propose that WT1 regulates SRY in the initial sex determination process in humans and activates a cascade of genes ultimately leading to the complete organogenesis of the testis.

Molecular evolution of Sry and Sox gene

The mammalian Sry on the short arm of the Y chromosome encodes a nuclear factor-like protein harboring a DNA-binding domain known as the HMG box. The Sox genes encode similar factor like proteins, but the sequence similarity of the HMG box to that of Sry is variable as being at least 60%. The functional relationship of Sox to Sry genes with special reference to sex determination is unclear except for a few items such as human autosomal Sox9. Thus, it is significant to know more about the evolutionary in addition to the functional relationship between Sry and Sox genes for deepening and broadening our understanding concerning primary sex determination. Therefore, to clarify the ancestry and molecular evolution of the mammalian sex determining gene Sry with its evolutionary relationships to the Sox gene, a molecular phylogenetic tree for the HMG box superfamily was constructed and analyzed, and the following conclusions were reached: (1) The nuclear non histone HMG proteins are supposedly the oldest, appearing at least more than one billion years ago, before the divergence of animals and plants. They diverged into two subgroups: one contains HMG14 and HMG17, and the other one contains HMG1 and HMG2 with various other genes. Subsequent divergences include the nucleolar UBF, nuclear SSRP as well as fungal mating protein Mc, MAT and Ste11. (2) The Sox and Sry genes diverged following the diversification of lymphoid transcription factors TCF and LEF. The Sry gene might have definitely evolved from the Sox gene cluster a few hundred million years ago. Additionally, the marsupial Sry, e.g. from Wallabie's and Dunnart's, is distinguished by being distant from eutherian Sry, but being closely related to the Sox gene cluster. (3) Molecular evolutionary rates estimated in mammalian Sry as the divergent rate per 100 million years are much higher than in Sox genes or other genes from the HMG box superfamily. This rapid evolution of Sry might agree with the fact that the Srys are present not on the pseudoautosomal region but on the distal region with no recombination of the Y chromosomal short arm.

Sugar and spice or slugs and snails?

Over the past 500 million years or so, metazoans have evolved a bewildering diversity of genetic mechanisms for generating that most interesting of phenotypes — the difference between girls and boys. Despite intense effort, a conserved sex-determination effector gene has proven elusive. Until recently, the evidence indicated that completely different molecular mechanisms and proteins regulate sexual dimorphism in different phyla; sex-specific RNA splicing in flies, a signal transduction cascade in worms and a male-determining DNA-binding protein in mammals. Could it be that the quest is now over and a single unifying gene is at the bottom of it all?Recent evidence from studies on a class of transcription factors known as DM-domain proteins has implicated a common effector in the regulation of male-specific characteristics in flies, nematodes, reptiles, birds and mammals. Mutations in the Drosophila doublesex (dsx) and Caenorhabditis elegans mab-3 genes lead to defects in a variety of male-specific processes. As well as being functionally interchangeable, the genes regulate similar male-specific biological processes, such as repressing yolk-protein synthesis and eliciting the development of a sex-specific nervous system. Furthermore, a vertebrate DM-domain gene, DMRT1, which is associated with a small interval of chromosome 9 required for human testis development, exhibits male-specific expression in the gonads of chickens and alligators. This indicates that diverged sex-determining mechanisms might converge at a common effector gene that functions to promote male development.Raymond et al. 1xDmrt1, a gene related to worm and fly sexual regulators, is required for mammalian testis differentiation. Raymond, C.S. et al. Genes Dev. 2000; 14: 2587–2595Crossref | PubMed | Scopus (374)See all References1 have examined this possibility by generating mice with mutations in Dmrt1. They report that, whereas female development is normal in mouse Dmrt1 knockouts, the differentiation of the testis is obviously not. Testis differentiation is the key event in mammalian sex determination, in particular the formation of a somatic support-cell lineage known as Sertoli cells. It is thought that the mammalian sex-determining gene Sry acts to promote the differentiation of Sertoli cells, and that these influence the subsequent events in testis differentiation. In Dmrt1-mutant males, the testes appear normal at birth, but by the onset of germ-cell meiosis a few days later, abnormalities are apparent. After two weeks, the mutant testes are filled with immature Sertoli cells, a phenotype resembling that observed in human chromosome 9-deficient males.Thus, it appears that a DM-domain gene functions as a downstream effector in vertebrate sexual differentiation in a way analogous to that observed in invertebrates. Interestingly, the chromosome 9 interval associated with DMRT1 in humans contains at least two other DM-domain genes. The situation in the mouse is not clear, but it could be that multiple DM-domain genes have evolved in mammals to ensure correct male differentiation. Clearly, a functional analysis of DMRT1 in other organisms will go a long way to confirm whether the evolution of sexual dimorphism has, after all, been conserved.

Sequence-specific High Mobility Group Box Factors Recognize 10–12-Base Pair Minor Groove Motifs

Sequence-specific High Mobility Group Box Factors Recognize 10–12-Base Pair Minor Groove Motifs

The human SOX18 gene: cDNA cloning and high resolution mapping

SOX genes comprise a family of genes that are related to the mammalian sex determining gene SRY and these genes play key roles during animal development. We report here cloning and characterisation of the human SOX18 gene. SOX18 gene is expressed in foetal brain as well as in a wide range of foetal and adult tissues indicating its function is not restricted to early development. Mapping analysis has revealed that SOX18 gene is located on human chromosome 20q13.3, 27.29 cR distal from the marker D20S173.

A subtractive gene expression screen suggests a role forvanin-1 in testis development in mice

The molecular pathways leading from indifferent mammalian gonad to either testis or ovary are not well understood. A number of genes, including the Y-linked sex determining gene SRY, have been shown to play roles in sex determination or differentiation, but there are clearly many missing elements to be found. We used suppression-subtractive hybridization to construct normalized cDNA libraries enriched for male-specific or female-specific transcripts in mouse fetal gonads. We describe the strategy used to efficiently screen these libraries for candidate sex-determination and gonadogenesis genes. One gene arising from these screens is vanin-1, which encodes a protein implicated in the induction of cell migration into the thymus. We find that vanin-1 is expressed male-specifically in Sertoli cells of the developing testis and may be involved in inducing cell migration from the adjacent mesonephros, a process known to be critical for testis development. This screening approach is likely to be applicable to the isolation and study of genes involved in a variety of developmental systems.