Method: 1) Both Osx-lacZ knock-in, Osx-GFP:Cre/Rosa 26 mice, and immunohistochemistry were used for tracing Osx expression patterns during condyle development; 2) conditional osterix-null mice were generated by crossing osterix loxP mice to the 2.3 Col I-Cre mice; and 3) combined approaches of x-ray, micro-CT, and histology methods were used to characterize the mandibular condyle phenotypes.
Result: 1) X-gal staining of Osx lacZ knock-in, and Osx-GFP:Cre/Rosa 26 mice showed that Osx was widely expressed in the rest cell zone, proliferation cell zone, hypertrophic cell zone and osteoblasts in condyle; 2) Conditional deletions of osterix led to a malformed mandibular condyle, including i) decreased size of condyle head, decreased bone volume in both condyle head and neck; ii) HE and safranin O staining showed an increased width of the hypertrophic cell zone; and iii) in situ hybridization revealed an increased levels of collagen II and collagen X mRNA expression in Osx cKO condylar cartilage.
Conclusion: Osterix plays important roles in mandibular condyle formation through its dual roles in control of both osteogenesis and chondrogenesis (Work supported by NIH grant DE018486 to JQF).
Keywords: Cartilage, Growth & development and osterix, condyle
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