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Mol. Cell. Biol., Apr 1997, 2336-2346, Vol 17, No. 4
V Lefebvre, W Huang, VR Harley, PN Goodfellow and B de Crombrugghe
The identification of mutations in the SRY-related SOX9 gene in patients
with campomelic dysplasia, a severe skeletal malformation syndrome, and the
abundant expression of Sox9 in mouse chondroprogenitor cells and fully
differentiated chondrocytes during embryonic development have suggested the
hypothesis that SOX9 might play a role in chondrogenesis. Our previous
experiments with the gene (Col2a1) for collagen II, an early and abundant
marker of chondrocyte differentiation, identified a minimal DNA element in
intron 1 which directs chondrocyte-specific expression in transgenic mice.
This element is also a strong chondrocyte-specific enhancer in transient
transfection experiments. We show here that Col2a1 expression is closely
correlated with high levels of SOX9 RNA and protein in chondrocytes. Our
experiments indicate that the minimal Col2a1 enhancer is a direct target
for Sox9. Indeed, SOX9 binds to a sequence of the minimal Col2a1 enhancer
that is essential for activity in chondrocytes, and SOX9 acts as a potent
activator of this enhancer in cotransfection experiments in nonchondrocytic
cells. Mutations in the enhancer that prevent binding of SOX9 abolish
enhancer activity in chondrocytes and suppress enhancer activation by SOX9
in nonchondrocytic cells. Other SOX family members are ineffective.
Expression of a truncated SOX9 protein lacking the transactivation domain
but retaining DNA-binding activity interferes with enhancer activation by
full-length SOX9 in fibroblasts and inhibits enhancer activity in
chondrocytes. Our results strongly suggest a model whereby SOX9 is involved
in the control of the cell-specific activation of COL2A1 in chondrocytes,
an essential component of the differentiation program of these cells. We
speculate that in campomelic dysplasia a decrease in SOX9 activity would
inhibit production of collagen II, and eventually other cartilage matrix
proteins, leading to major skeletal anomalies.
Copyright © 1997, American Society for Microbiology
SOX9 is a potent activator of the chondrocyte-specific enhancer of the pro alpha1(II) collagen gene
Department of Molecular Genetics, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
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