Expression of SOX9 and COL2A1 on ATRA-treated rat hind limb bud mesenchymal cells. A: Cells were cultured in medium with 0, 0.01, 0.1, 1 and 10 μM ATRA for 24 h, then detected mRNA transcript levels of SOX9 and COL2A1 by qRT-PCR. ATRA dose-dependently downregulates the mRNA transcript levels of SOX9 and COL2A1. B: Cells were cultured in medium with 0, 0.01, 0.1, 1 and 10 μM ATRA for 24 h, then detected protein levels of SOX9 and COL2A1 by western blotting. ATRA dose-dependently downregulates the protein levels of SOX9 and COL2A1. Data are presented as the mean ± SD for at least three independent experiments done in triplicate. *P<0.05 compared to the control.