Article

Haploinsufficiency of Sox9 results in defective cartilage primordia and premature skeletal mineralization

Department of Molecular Genetics and Graduate Program in Genes and Development, M. D. Anderson Cancer Center, University of Texas, Houston, TX 77030, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 07/2001; 98(12):6698-703. DOI: 10.1073/pnas.111092198
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ABSTRACT In humans, SOX9 heterozygous mutations cause the severe skeletal dysmorphology syndrome campomelic dysplasia. Except for clinical descriptions, little is known about the pathogenesis of this disease. We have generated heterozygous Sox9 mutant mice that phenocopy most of the skeletal abnormalities of this syndrome. The Sox9(+/-) mice died perinatally with cleft palate, as well as hypoplasia and bending of many skeletal structures derived from cartilage precursors. In embryonic day (E)14.5 heterozygous embryos, bending of radius, ulna, and tibia cartilages was already prominent. In E12.5 heterozygotes, all skeletal elements visualized by using Alcian blue were smaller. In addition, the overall levels of Col2a1 RNA at E10.5 and E12.5 were lower than in wild-type embryos. We propose that the skeletal abnormalities observed at later embryonic stages were caused by delayed or defective precartilaginous condensations. Furthermore, in E18.5 embryos and in newborn heterozygotes, premature mineralization occurred in many bones, including vertebrae and some craniofacial bones. Because Sox9 is not expressed in the mineralized portion of the growth plate, this premature mineralization is very likely the consequence of allele insufficiency existing in cells of the growth plate that express Sox9. Because the hypertrophic zone of the heterozygous Sox9 mutants was larger than that of wild-type mice, we propose that Sox9 also has a role in regulating the transition to hypertrophic chondrocytes in the growth plate. Despite the severe hypoplasia of cartilages, the overall organization and cellular composition of the growth plate were otherwise normal. Our results suggest the hypothesis that two critical steps of the chondrocyte differentiation pathway are sensitive to Sox9 dosage. First, an early step presumably at the stage of mesenchymal condensation of cartilage primordia, and second, a later step preceding the transition of chondrocytes into hypertrophic chondrocytes.

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    • "The ABC transporters are essential for many processes in the cell, driving the transport of various molecules through ATP hydrolysis (Dean et al., 2001). Previously associated with embryo development (Asou et al., 2002), the sex determining region Y box 9 gene (SOX9) causes severe bone defects and perinatal death in heterozygous mutant mice (Bi et al., 2001). The general but important activity of the ABC gene superfamily and the role of SOX9 on prenatal development make these "
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    • "Hence, several conditional mouse lines have been generated in the past for this important developmental control gene (Yap et al. 2011; Kist et al. 2002). Furthermore, alleles with a knock-in of an IRES-lacZ (Bi et al. 2001) IRESenhanced green fluorescent protein (EGFP) (Chan et al. 2011; Nel-Themaat et al. 2009) or F2A-EGFP (Chan et al. 2011) as well as a tamoxifen-inducible Cre-recombinase (CreERT2) (Soeda et al. 2010) into the Sox9 locus have been described to facilitate the analyis of such a pleiotropic gene. While the existing Sox9-cKO alleles lack the insertion of a reporter gene, the existing Sox9 reporter gene knock-in lines are generated as non-conditional alleles. "
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    • "SOX9 markedly inhibited activation of Wnt/í µí»½-catenin-dependent promoters and stimulated degradation of í µí»½-catenin [72] by directing intracellular degradation, thus, favoring chondrocyte differentiation and delaying hypertrophic chondrocytes differentiation [69]. Studies performed on embryos in different stages of gestation evidenced that SOX9 and Runx2 control the transition from prehypertrophic to hypertrophic chondrocytes [73]. It has been demonstrated that upregulation of type X collagen (col10a1), typical hypertrophic marker, is also regulated by overexpression of Wnt8c, Wnt9a and í µí»½-catenin that inhibited SOX9 and type II collagen (col2a1) and induced Runx2 trascription factor [74]. SOX9 and Runx2 physically interact in MSC and while SOX9 can inhibit Runx2 transactivation, on the other hand, Runx2 exerts reciprocal inhibition on SOX9 transactivity [72]. "
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