Mammalian Sex-determining Gene SRY Research Articles

Two rather than one

Sex Determination For several decades, it has been believed that the mammalian sex-determining gene Sry contains a single exon. Miyawaki et al. have now identified a cryptic second exon of mouse Sry . Loss- and gain-of-function analyses revealed that the two-exon SRY (SRY-T), not the canonical single exon–encoded SRY (SRY-S), is the bona fide testis-determining factor. Sry exon2 is composed of retrotransposon-derived sequences. The SRY-S carboxyl terminus contains a degradation sequence (degron), whereas the SRY-T carboxyl terminus encoded in the Sry exon2 is degron free, thereby conferring protein stability on SRY-T. Science , this issue p. [121][1] [1]: /lookup/doi/10.1126/science.abb6430

Evolution of the sex-determining gene in the teleostean genus Oryzias

In the genetic sex determination of vertebrates, the gonadal sex depends on the combination of sex chromosomes that a zygote possesses. Despite the discovery of the sex-determining gene (SRY/Sry) in mammals in 1990s, the sex-determining gene in non-mammalian vertebrates remained an enigma for over a decade. In most mammals, the male-inducing master sex-determining gene is located on the Y chromosome and is therefore absent from XX females. A second sex-determining gene, Dmy, was described in the Oryzias latipes in 2002 and has a DNA-binding motif that is different from the motif in the mammalian sex-determining gene SRY or Sry. Dmy is also located on the Y chromosome and is therefore absent in XX females. Seven other sex-determining genes, including candidate genes, are now known in birds, a frog species, and 5 fish species. These findings over the past twenty years have increased our knowledge of sex-determining genes and sex chromosomes among vertebrates. Here, we review recent advances in our understanding of sex-determining genes and genetic sex determination systems in fish, especially those of the Oryzias species, which are described in detail. The facts suggest some patterns of how new sex-determining genes emerged and evolved. We believe that these facts are common not only in Oryzias but also in other fish species. This knowledge will help to elucidate the conserved mechanisms from which various sex-determining mechanisms have evolved.

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.

Multiple copies of SRY on the large Y chromosome of the Okinawa spiny rat, Tokudaia muenninki

The Okinawa spiny rat, Tokudaia muenninki, is the only species with a Y chromosome in the genus Tokudaia. Its phylogenic relationship with two XO/XO species, Tokudaia osimensis and Tokudaia tokunoshimensis, lacking a Y chromosome and the mammalian sex-determining gene SRY, is unknown. Furthermore, there has been little cytogenetic analysis of the sex chromosomes in T. muenninki. Therefore, we constructed molecular phylogenetic trees with nucleotide sequences of cyt b, RAG1, and IRBP. All trees strongly supported that T. muenninki was the first to diverge from the Tokudaia ancestor, indicating that loss of the Y chromosome and SRY occurred in the common ancestor of the two XO/XO species after T. muenninki diverged. We found that the X and Y chromosomes of T. muenninki consisted of large euchromatic and heterochromatic regions by conducting G- and C-banding analyses. PCR, Southern blotting, and FISH revealed that T. muenninki males had multiple SRY copies on the long arm of the Y chromosome. At least three of 24 SRY sequences contained a complete open reading frame (ORF). A species-specific substitution from alanine to serine was found in all copies at the DNA-binding surface within the HMG-box, suggesting that it occurred in an original SRY.

The process of a Y-loss event in an XO/XO mammal, the Ryukyu spiny rat

The Ryukyu spiny rat, Tokudaia osimensis, has an XO/XO sex chromosome constitution, lacking a Y chromosome and the mammalian sex-determining gene SRY. To investigate the Y-loss event, we traced three proto-Y-linked genes, RBMY1A1, EIF2S3Y, and KDM5D, in the genome. The original Y-linked RBMY1A1 was lost as well as SRY, and the remaining RBMY1A1 was a processed pseudogene on autosome. In contrast, EIF2S3Y and KDM5D were conserved in genomes of both sexes as a result of their translocation from the Y chromosome to the X chromosome and/or autosomes. Furthermore, these genes were expressed in gonads and brains of both sexes. Our study indicated a loss of Y-linked genes with important male functions to be necessary for the Y chromosome to disappear. These functions might have been retained through the acquisition of new genes, and therefore, the Y-loss has had no harmful effect on the maintenance of this species.

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.

HMG box containing transcription factors in lymphocyte differentiation

The identification of the mammalian sex-determining gene Sry has led to the discovery of a large family of related (`HMG box') transcription factors that control developmental events in yeast, C. elegans, Drosophila and vertebrates. In lymphocyte differentiation, several HMG box proteins play a decisive role. Sox-4 is important for very early B-cell differentiation, while TCF-1/LEF-1 play a crucial role in early thymocyte development. TCF/LEF proteins have recently been found to constitute a downstream component of the Wingless/Wnt signal transduction pathway. In flies, this pathway controls segment polarity; in Xenopus it controls the definition of the body axis. Deregulation of the pathway occurs in several human tumors. These insights in the molecular events that are involved in TCF/LEF function in these organisms may eventually lead to the understanding of the function of these HMG box proteins in lymphoid development.

Rapid sequence evolution of the mammalian sex-determining gene SRY: Nature 364, 713–715

In mammals, induction of male sex determination requires the Y-chromosome gene SRY. SRY encodes a protein with a central 'high mobility group' domain (HMG box) of about 78 amino acids. HMG boxes are found in a wide variety of proteins that bind to DNA with high affinity but differing degrees of sequence specificity. The human SRY protein binds to linear DNA with sequence specificity and to cruciform DNA structures without sequence specificity. The DNA-binding activity of the SRY protein resides in the HMG box and mutations in this region are associated with sex reversal in XY females. No function has been ascribed to the portions of the SRY protein outside the HMG box. SRY belongs to a family of genes that are related by sequence homology within the DNA-binding domain: the genes most similar to SRY (> 60%) have been named SOX genes (SRY box genes). None of the known SOX genes is homologous to SRY outside the HMG-box region. Although SRY is an important developmental regulator, its sequence is poorly conserved between species apart from the HMG-box domain. Here we investigate the coding sequence of SRY in primates and find that evolution has been rapid in the regions flanking the conserved domain. The high degree of sequence divergence and the frequency of non-synonymous mutations suggest either that the majority of the coding sequence has no functional significance or that directional selection has occurred.

Rapid sequence evolution of the mammalian sex-determining gene SRY.

In mammals, induction of male sex determination requires the Y-chromosome gene SRY. SRY encodes a protein with a central 'high mobility group' domain (HMG box) of about 78 amino acids. HMG boxes are found in a wide variety of proteins that bind to DNA with high affinity but differing degrees of sequence specificity. The human SRY protein binds to linear DNA with sequence specificity and to cruciform DNA structures without sequence specificity. The DNA-binding activity of the SRY protein resides in the HMG box and mutations in this region are associated with sex reversal in XY females. No function has been ascribed to the portions of the SRY protein outside the HMG box. SRY belongs to a family of genes that are related by sequence homology within the DNA-binding domain: the genes most similar to SRY (> 60%) have been named SOX genes (SRY box genes). None of the known SOX genes is homologous to SRY outside the HMG-box region. Although SRY is an important developmental regulator, its sequence is poorly conserved between species apart from the HMG-box domain. Here we investigate the coding sequence of SRY in primates and find that evolution has been rapid in the regions flanking the conserved domain. The high degree of sequence divergence and the frequency of non-synonymous mutations suggest either that the majority of the coding sequence has no functional significance or that directional selection has occurred.

Sequence-specific interaction of the HMG box proteins TCF-1 and SRY occurs within the minor groove of a Watson-Crick double helix.

The high mobility group I (HMG) box is proposed to mediate DNA binding in a novel group of transcription-regulating proteins. Two of these, the proteins encoded by the T cell-specific TCF-1 and the mammalian sex-determining gene SRY, carry a single HMG box with specificity for the heptamer motif A/T A/T C A A A G. We have now analysed the mode of interaction of the HMG boxes of TCF-1 and SRY with this motif. Methylation interference footprinting revealed that both HMG boxes contacted adenines on both strands in the minor groove, whereas no major groove guanine contacts were discerned. Diethylpyrocarbonate (DEPC) carbethoxylation interference footprinting of TCF-1 indicated the absence of major groove contacts on positions 5, 6 and 7 of the motif. Carbethoxylation interference was observed, however, on positions 2, 3 and 4 and to a lesser extent on position 1 in the major groove. Combined T----C and A----I substitution, which changes the surface of the major groove but leaves the minor groove intact, did not interfere with sequence-specific binding by TCF-1 and SRY. These observations indicate that recognition of the heptamer motif by the HMG boxes of the distantly related TCF-1 and SRY proteins predominantly occurs through nucleotide contacts in the minor groove.

Identification and cloning of TCF-1, a T lymphocyte-specific transcription factor containing a sequence-specific HMG box.

CD3-epsilon expression is controlled by a downstream T lymphocyte-specific enhancer element. We report the identification of a T cell-specific transcription factor, TCF-1, binding to this element. The multimerized recognition motif of TCF-1 constituted a T cell-specific enhancer. Subsequent cloning of TCF-1 identified three splice alternatives. TCF-1 contained a single DNA-binding HMG box most closely related to similar boxes in the putative mammalian sex-determining gene SRY and in the Schizosaccharomyces pombe Mc mating type gene. TCF-1 mRNA was expressed uniquely in T lymphocytes. Upon cotransfection into non-T cells, TCF-1 could transactivate through its cognate motif. These results identify TCF-1 as a T cell-specific transcription factor, which might play a role in the establishment of the mature T cell phenotype.