Bone Abstracts

Members of the Rho family including small GTPase Cdc42 have been shown to play multiple roles in cell regulation, including regulation of cytoskeletal organization, cell migration, proliferation, and apoptosis. However, their tissue-specific roles in vivo, especially in limb bud mesenchyme, remain largely unknown. Herein, we report that conditional deletion of Cdc42 in AER dose not change the limb development, however, knockout of Cdc42 in mesenchymal stem cells of limb bud (PrxCre;Cdc42^f/f) results in a severe phenotype of bone formation. Knockout of Cdc42 demonstrated short limbs and body, abnormal calcification of the cranium. Severe defects were also found in long bone growth plate cartilage, characterized by loss of columnar organization of chondrocytes, and thickening and massive accumulation of hypertrophic chondrocytes, resulting in delayed endochondral bone formation. Analysis of micromass cultures suggest that deletion of Cdc42 in C3H10T1/2 leads to defects in cartilage condensation and reducing the expression of N-cadherin, p-Smad1/5 and p-p38, suggesting that Cdc42 regulates the mesenchymal stem cells condensation via BMP and p38 signaling. In situ hybridization analysis revealed that expression patterning of Col10, Ihh, PTHRPr and Mmp13 were changed. Our results demonstrated that knock-down of Cdc42 in the chondrocyte cell line ATDC5 resulted in earlier induction of hypertrophic markers, such as Col10 expression and matrix mineralization. The results point out that Cdc42 regulates prehypertrophy via PI3K-AKT signaling and undergo vigorous apoptosis. These results demonstrate that Cdc42 is essential for bone development, especially the cartilage formation.