Male specific expression suggests role of DMRT1 in human sex determination.

Sex determination in mammals is controlled by various transcription factors. Following the identification of SRY on the Y chromosome, several other factors have been identified. They can normally be identified as being involved in sex determination by the identification of sex reversal mutations or deletions, functional studies, and also by male-specific expression patterns in embryos. Here, it is shown that DMRT1, recently demonstrated to be deleted in 9p monosomies associated with sex reversal, is specifically expressed during sex determination in the genital ridge of human male, but not female, embryos, similar to SRY.

Direct interaction of SRY-related protein SOX9 and steroidogenic factor 1 regulates transcription of the human anti-Müllerian hormone gene.

For proper male sexual differentiation, anti-Müllerian hormone (AMH) must be tightly regulated during embryonic development to promote regression of the Müllerian duct. However, the molecular mechanisms specifying the onset of AMH in male mammals are not yet clearly defined. A DNA-binding element for the steroidogenic factor 1 (SF-1), a member of the orphan nuclear receptor family, located in the AMH proximal promoter has recently been characterized and demonstrated as being essential for AMH gene activation. However, the requirement for a specific promoter environment for SF-1 activation as well as the presence of conserved cis DNA-binding elements in the AMH promoter suggest that SF-1 is a member of a combinatorial protein-protein and protein-DNA complex. In this study, we demonstrate that the canonical SOX-binding site within the human AMH proximal promoter can bind the transcription factor SOX9, a Sertoli cell factor closely associated with Sertoli cell differentiation and AMH expression. Transfection studies with COS-7 cells revealed that SOX9 can cooperate with SF-1 in this activation process. In vitro and in vivo protein-binding studies indicate that SOX9 and SF-1 interact directly via the SOX9 DNA-binding domain and the SF-1 C-terminal region, respectively. We propose that the two transcription factors SOX9 and SF-1 could both be involved in the expression of the AMH gene, in part as a result of their respective binding to the AMH promoter and in part because of their ability to interact with each other. Our work thus identifies SOX9 as an interaction partner of SF-1 that could be involved in the Sertoli cell-specific expression of AMH during embryogenesis.

The SOX10/Sox10 gene from human and mouse: sequence, expression, and transactivation by the encoded HMG domain transcription factor.

The SOX genes form a gene family related by homology to the high-mobility group (HMG) box region of the testis-determining gene SRY. We have cloned and sequenced the SOX10 and Sox10 genes from human and mouse, respectively. Both genes encode proteins of 466 amino acids with 98% sequence identity. Significant expression of the 2.9-kb human SOX10 mRNA is observed in fetal brain and in adult brain, heart, small intestine and colon. Strong expression of Sox10 occurs throughout the peripheral nervous system during mouse embryonic development. SOX10 shows an overall amino acid sequence identity of 59% to SOX9. Like SOX9, SOX10 has a potent transcription activation domain at its C-terminus and is therefore likely to function as a transcription factor. Whereas SOX9 maps to 17q, a SOX10 cosmid has previously been mapped by us to the region 22q13.1. Mutations in SOX10 have recently been identified as one cause of Waardenburg-Hirschsprung disease in humans, while a Sox10 mutation underlies the mouse mutant Dom, a murine Hirschsprung model.

Two independent nuclear localization signals are present in the DNA-binding high-mobility group domains of SRY and SOX9.

SRY and SOX9, members of the family of high-mobility group (HMG) domain transcription factors, are both essential for testis formation during human embryonic development. The HMG domain is a DNA-binding and DNA-bending motif comprising about 80 amino acid residues. It has been shown that SRY and SOX9 are nuclear proteins. Using normal or mutant SRY-beta-galactosidase and SOX9-beta-galactosidase fusion proteins in transfection studies involving COS-7 cells, we have identified two nuclear localization signals (NLSs) within the HMG domains of both proteins that can independently direct the fusion proteins into the nucleus. Only mutational inactivation of both NLS motifs resulted in complete exclusion of the fusion proteins from the nucleus. The NLS sequences are located at the N and C termini of the HMG domain and are a bipartite NLS motif and a basic cluster NLS motif, respectively. Both NLS motifs are conserved in the HMG domains of other transcription factors. The implications of the present results are discussed regarding (a) the apparent dual function of certain basic amino acid residues in the HMG domain of SRY in both DNA binding and in nuclear localization and (b) the possible control of SOX9 in early gonadal differentiation at the level of nuclear translocation.

Mutational analysis of the SOX9 gene in campomelic dysplasia and autosomal sex reversal: lack of genotype/phenotype correlations.

It has previously been shown that, in the heterozygous state, mutations in the SOX9 gene cause campomelic dysplasia (CD) and the often associated autosomal XY sex reversal. In 12 CD patients, 10 novel mutations and one recurrent mutation were characterized in one SOX9 allele each, and in one case, no mutation was found. Four missense mutations are all located within the high mobility group (HMG) domain. They either reduce or abolish the DNA-binding ability of the mutant SOX9 proteins. Among the five nonsense and three frameshift mutations identified, two leave the C-terminal transactivation (TA) domain encompassing residues 402-509 of SOX9 partly or almost completely intact. When tested in cell transfection experiments, the recurrent nonsense mutation Y440X, found in two patients who survived for four and more than 9 years, respectively, exhibits some residual transactivation ability. In contrast, a frameshift mutation extending the protein by 70 residues at codon 507, found in a patient who died shortly after birth, showed no transactivation. This is apparently due to instability of the mutant SOX9 protein as demonstrated by Western blotting. Amino acid substitutions and nonsense mutations are found in patients with and without XY sex reversal, indicating that sex reversal in CD is subject to variable penetrance. Finally, none of 18 female patients with XY gonadal dysgenesis (Swyer syndrome) showed an altered SOX9 banding pattern in SSCP assays, providing evidence that SOX9 mutations do not usually result in XY sex reversal without skeletal malformations.

Sex reversal by loss of the C-terminal transactivation domain of human SOX9.

Haploinsufficiency for SOX9 has recently been identified as the cause for both campomelic dysplasia (CD), a human skeletal malformation syndrome, and the associated autosomal XY sex reversal. SOX9 contains a putative DNA-binding motif known as the high-mobility group (HMG) domain characterizing a whole class of transcription factors. We show in cell transfection experiments that SOX9 can transactivate transcription from a reporter plasmid through the motif AACAAAG, a sequence recognized by other HMG domain transcription factors. By fusing all or part of SOX9 to the DNA-binding domain of yeast GAL4, the transactivating function was mapped to a transcription activation (TA) domain at the C terminus of SOX9. This non-acidic TA domain is evolutionarily conserved and rich in proline, glutamine and serine. With one exception, all SOX9 nonsense and frame shift mutations described so far in CD/sex reversal patients lead to truncation of the TA domain, suggesting that impairment of gonadal and skeletal development in these cases results, at least in part, from loss of transactivation of genes downstream of SOX9.