The relative expression of four osteogenic genes under the different treatments.

1) no ATRA, no BMP-2/7; 2) 1 µM ATRA, no BMP-2/7; 3) 1 µM ATRA, 5 ng/ml BMP-2/7; 4) 1 µM ATRA, 50 ng/ml BMP-2/7; 5) no ATRA, 5 ng/ml BMP-2/7; 6) no ATRA, 50 ng/ml BMP-2/7 for 1 day, 4 days and 7 days. (A) Runx2; (B) Collagen I; (C) Alkaline phosphatase; (D) Osteocalcin. The gene expression was first normalized to the corresponding β-actin gene expression for each sample. Then all the gene data were normalized to the gene data in control group on the 1st day. All data are presented as mean values together with the standard deviation (SD). *: p<0.05, **: p<0.01, ***: p<0.001.