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

• Published in: Human molecular genetics Vol. 12; no. 14; pp. 1755 - 1765
• Main Authors: Bernard, Pascal, Tang, Paisu, Liu, Siyuan, Dewing, Phoebe, Harley, Vincent R., Vilain, Eric
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 15-07-2003; Oxford Publishing Limited (England)
• Subjects: Biological and medical sciences; Bone and Bones - abnormalities; Chondrogenesis - physiology; DNA-Binding Proteins - metabolism; Fundamental and applied biological sciences. Psychology; Fushi Tarazu Transcription Factors; High Mobility Group Proteins - genetics; High Mobility Group Proteins - metabolism; Homeodomain Proteins; Humans; Infant, Newborn; Male; Molecular and cellular biology; Mutation; Protein Binding; Receptors, Cytoplasmic and Nuclear; Sex Determination Processes; SOX9 Transcription Factor; Steroidogenic Factor 1; Transcription Factors - genetics; Transcription Factors - metabolism; Genetics
• ISSN: 0964-6906; 1460-2083; 1460-2083
• DOI: 10.1093/hmg/ddg182

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.