Dimerization of SOX9 is required for chondrogenesis, but not for sex determination

Abstract

The SRY-related SOX9 gene is involved in both chondrogenesis and the early steps of mammalian sex determination. Mutations in the human SOX9 gene cause campomelic dysplasia, a severe skeletal malformation syndrome associated with male-to-female sex reversal in most, but not all, XY individuals. Here we show that SOX9 contains a dimerization domain, and binds co-operatively as a dimer in the presence of the DNA enhancer element in genes involved in chondrocyte differentiation, such as Col11a2 and Col9a2, but binds as a monomer to the regulatory region of the sex-determining gene SF1. Frameshift SOX9 mutations truncate its two activation domains, while all missense mutations reported to date lie in the high mobility group (HMG) DNA-binding domain. We identify a missense mutation (A76E), the first outside the HMG domain, in an XY patient presenting with campomelic dysplasia but without sex reversal. This mutation disrupts the dimerization capability of SOX9, interfering with both the DNA binding and consequent transactivation of both the Col11a2 and Col9a2 enhancers. Consistent with the patient's phenotype, the A76E mutation does not affect DNA binding and activation of the SF1 enhancer. DNA-dependent cooperative dimerization could represent a novel mechanism to achieve tissue-specific regulation of gene expression by a SOX transcription factor. These results establish that SOX9 cooperative dimerization is required for chondrogenesis but not for sex determination and may explain why campomelic dysplasia need not be associated with XY sex reversal.

Testicular dysgenesis/regression without campomelic dysplasia in patients carrying missense mutations and upstream deletion of SOX9

“…Colored boxes in the lower panel indicate dimerization (codon 60–101) (Bernard et al. 2003), high‐mobility group ( HMG : codon 101–184), proline/glutamine/alanine ( PQA : codon 339–379), and proline/glutamine/serine‐rich ( PQS ‐rich: codon 386–509) domains (McDowall et al. 1999).…”

“…Patients with SOX9 mutations manifest campomelia, hypoplastic scapulae, pelvic anomalies, micrognathia, and cleft palate, collectively referred to as campomelic dysplasia (CD), although a certain percentage of mutation‐positive patients show a mild variant of CD that lacks campomelia (acampomelic CD: ACD) (Bernard et al. 2003; Michel‐Calemard et al. 2004; Staffler et al.…”

Overexpression of SOX9 in mouse embryonic stem cells directs the immediate chondrogenic commitment

“…However, the expression of collagen IIA was detected at relatively basal levels, suggesting other cofactors and optimal differentiation culture conditions may be needed to activate the gene sufficiently. In fact, SOX9 interacts with other cofactors, such as L-Sox5 and Sox6 for dimerization and subsequently activates cartilage-specific marker genes more effectively (Bernard et al, 2003;Ikeda et al, 2004). mES cells exhibit the very unique distribution of cell cycle: 15% in G1, 75% in S, and 10% in G2/M, respectively, supporting their infinite proliferation potentials in vitro without differentiation under LIF signals (Savatier et al, 2002).…”

“…SOX9 is the member of the SOX (Sry-type HMG box) family and predominantly expressed during mesenchymal condensation and cartilage formation in mouse embryos (Wright et al, 1995). In addition, SOX9 is known to be a key regulator for the expression of collagen II, IX, XI, and aggrecan, the major matrix proteins specific for chondrocytes through binding to the enhancer region (Bell et al, 1997;Lefebvre et al, 1997;Bridgewater et al, 1998;Sekiya et al, 2000;Bernard et al, 2003). SOX9 has been also reported to be required for chondrogenesis by the generation of SOX9-mutant ES cells and chimeric mice (Bi et al, 1999).…”

Structure-aided prediction of mammalian transcription factor complexes in conserved non-coding elements

“…Traditional discovery of TF-TF cooperative interactions has typically involved detailed experimental dissection of one or a small number of promoter sequences [15][16][17]. Selected cases are further studied by crystallography, which has resulted in a steady but slow growth of TF complexes in the Protein Data Bank (PDB; approx.…”