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: 9.67). 07/2001; 98(12):6698-703. DOI: 10.1073/pnas.111092198
Source: PubMed

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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Available from: Deanne J Whitworth, Sep 03, 2014
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    • "Therefore, it is not possible to study SOX9 function during later development with a simple mouse knockout model in certain vertebrates . Instead, conditional mice knockout models, preventing Sox9 expression in specific cells and/or at specific times, are needed to study SOX9 protein function as development progresses (Bi et al. 2001; Akiyama et al. 2002). As with mice, humans with only one functional copy of SOX9 are haploinsufficient (Kwok et al. 1995). "

    Full-text · Article · Jan 2016 · Gene
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    • "In the first of a series of differentiation steps, neural crest cells entering the facial primordia form mesenchymal progenitors of bone and cartilage . Cell-type specificity is later initiated through the expression of the HMG box transcription factor Sox9 in cartilage precursors (Bi et al., 2001) or the sequential activity of the runt family member Runx2 (Komori et al., 1997) and the zinc finger transcription factor Osterix (Osx) (Nakashima et al., 2002) in osteoblast precursors. The outcome of these transcriptional programmes is the progression of precursor cell differentiation into bonafide chondroctyes or osteoblasts that in turn secrete extracellular matrix components and mineral specific to cartilage or bone. "
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    ABSTRACT: Nedd4 is an E3 ubiquitin ligase that has an essential role in craniofacial development. However, how and when Nedd4 controls skull formation is ill defined. Here we have used a collection of complementary genetic mouse models to dissect the cell-autonomous roles of Nedd4 in the formation of neural crest cell derived cranial bone. Removal of Nedd4 specifically from neural crest cells leads to profound craniofacial defects with marked reduction of cranial bone that was preceded by hypoplasia of bone forming osteoblasts. Removal of Nedd4 after differentiation of neural crest cells into progenitors of chondrocytes and osteoblasts also led to profound deficiency of craniofacial bone in the absence of cartilage defects. Notably, these skull malformations were conserved when Nedd4 was specifically removed from the osteoblast lineage after specification of osteoblast precursors from mesenchymal skeletal progenitors. We further show that absence of Nedd4 in pre-osteoblasts results in decreased cell proliferation and altered osteogenic differentiation. Taken together our data demonstrate a novel cell-autonomous role for Nedd4 in promoting expansion of the osteoblast progenitor pool to control craniofacial development. Nedd4 mutant mice therefore represent a unique mouse model of craniofacial anomalies that provide an ideal resource to explore the cell-intrinsic mechanisms of neural crest cells in craniofacial morphogenesis.
    Full-text · Article · Dec 2015 · Developmental Biology
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    • "Therefore, it is not possible to study SOX9 function during later development with a simple mouse knockout model in certain vertebrates . Instead, conditional mice knockout models, preventing Sox9 expression in specific cells and/or at specific times, are needed to study SOX9 protein function as development progresses (Bi et al. 2001; Akiyama et al. 2002). As with mice, humans with only one functional copy of SOX9 are haploinsufficient (Kwok et al. 1995). "
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    ABSTRACT: The SRY-related high-mobility box 9 (SOX9) gene is expressed in many different tissues. To better understand the DNA elements that control tissue-specific expression, we cloned and sequenced a 2.5 kb fragment lying 5' to the zebrafish sox9b gene transcriptional start site. Three regions of this clone contained stable secondary structures that hindered cloning, sequencing, and amplification. This segment, and smaller fragments, was inserted 5' of an EGFP reporter and transgenic fish were raised with the different reporters. Reporter expression was also observed in embryos directly injected with the constructs to transiently express the reporter. Heart expression required only a very short 5' sequence, as a 0.6 kb sox9b fragment produced reporter expression in heart in transgenic zebrafish, and transient experiments showed heart expression from a minimal sox9b promoter region containing a conserved TATA box and an EGR2 element (-74/+29 bp). Reporter expression in transgenic skeletal muscle was consistently lower than in other tissues. Jaw, brain, and notochord expression was strong with the full-length clone, but was dramatically reduced as the size of the fragment driving the reporter decreased from approximately 1.8 to 0.9 kb. The 2.5 kb region 5' of the sox9b contained 7 conserved non-coding elements (CNEs) that included putative hypoxia inducible factor 1α (HIF1α), CAAT box (CCAAT), early growth response protein 2 (EGR2), and core promoter elements. While a synthetic fragment containing all 7 CNEs produced some degree of reporter expression in muscle, jaw, heart and brain, the degree of reporter expression was considerably lower than that produced by the full length clone. These results can account for the tissue-specific expression of sox9b in the developing zebrafish.
    Full-text · Article · Dec 2015 · Gene
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