TAp63γ influences mouse cartilage development

Abstract

Depletion of tumor protein p63 results in severe epithelial as well as limb defects in mice, suggesting that p63 is also required for endochondral ossification during long bone development. A key stage in endochondral ossification is chondrocyte hypertrophy, which has been associated with elevated levels of the p63 variant TAp63 gamma. To investigate the role of TAp63 gamma in chondrocyte differentiation and maturation, we developed stable TAp63 gamma expressing ATDC5 cells. Compared to control cells, TAp63 gamma cells showed significant upregulation of Col10a1 after 4 and 7 days in culture. Moreover, alkaline phosphatase, Alizarin red, and Alcian blue staining were stronger in TAp63 gamma cells, suggesting that TAp63 gamma promotes chondrocyte proliferation, hypertrophic differentiation, and possibly matrix mineralization. To investigate the in vivo function of TAp63 gamma during endochondral bone formation, we established transgenic mice that express flag-tagged TAp63 gamma driven by Col10a1 regulatory elements. Skeletal staining of transgenic mice at postnatal day 1 showed accelerated ossification in long bone, tail, and digit bones compared to wild-type littermates. Furthermore, Sox9 expression was reduced and Runx2 expression was increased in the proliferative and/or hypertrophic zones of these mice. Altogether, these results suggest that TAp63 gamma promotes endochondral ossification and skeletal development, at least partially via controlling chondrocyte differentiation and maturation.