SOX9 Is an Activator and Repressor in Chondrocytes Figure 5. SOX9 directly represses Col10a1 in hypertrophic chondrocytes. (A) Clonal cell line MCTs-F expressing the Col10Flag-E was established from MCTs. (a) Immunohistochemistry indicated up-regulated Flag-tagged collagen X in growth arrested MCTs-F cells. (b) Flag signal in the cytosolic vesicles. (B) MCTs-F cells transfected with SOX9 expression vector (pSG-Sox9), or empty vector (pSG5). Expression of Col10a1 and Col10a1-Flag (36 bp longer in amplicon) was significantly reduced upon exogenous Sox9 expression (*, p#0.02). No RNA (2) or RNA from E16.5 Col10Flag-E expressing fetus (+) was used as control. (C) Strategy for activating ectopic Sox9 expression in hypertrophic chondrocytes. The pZ/Sox9 PLoS Genetics | www.plosgenetics.org 8 November 2011 | Volume 7 | Issue 11 | e1002356