ATRA up-regulates ROCK2 expression in hind limb bud mesenchymal cells. A: The effects of 24 h ATRA (1 μM) treatment on HOXD9, SHH, BSP, BMP4, MLC-2, HES-1, ROCK1 and ROCK2 measured by qRT-PCR. The expression level of each factor is expressed as a percentage. The effect of ATRA has a obvious correlation with the expression of ROCK2. B: ATRA dose-dependently upregulates mRNA transcript levels for ROCK2, and 1 μM ATRA caused the greatest increase among the concentrations tested. Data are presented as the mean ± SD for at least three independent experiments done in triplicate. *P<0.05 compared to the control.