SOX9 DIRECTLY REGULATES THE TYPE-II COLLAGEN GENE

Mutations in human SOX9 are associated with campomelic dysplasia (CD), characterised by skeletal malformation and XY sex reversal(1-3). Duri ng chondrogenesis in the mouse, Sox9 is coexpressed with Col2a1, the g ene encoding type-II collagen, the major cartilage matrix protein(4). Col2a1 is therefore a candidate regulatory target of SOX9. Regulatory sequences required for chondrocyte-specific expression of the type-II collagen gene have been localized to conserved sequences in the first intron in rats, mice and humans(5-8). We show here that SOX9 protein b inds specifically to sequences in the first intron of human COL2A1, Mu tation of these sequences abolishes SOX9 binding and chondrocyte-speci fic expression of a COL2A1-driven reporter gene (COL2A1-lacZ) in trans genic mice. Furthermore, ectopic expression of Sox9 trans-activates bo th a COL2A1-driven reporter gene and the endogenous Col2a1 gene in tra nsgenic mice. These results demonstrate that COL2A1 expression is dire ctly regulated by SOX9 protein in vivo and implicate abnormal regulati on of COL2A1 during chondrogenesis as a cause of the skeletal abnormal ities associated with campomelic dysplasia.