Quantitative real-time PCR analysis of gene expression in response to varying concentrations of growth factors. (A) BM-MSCs and (B) AD-MSCs were seeded in type I collagen gels and stimulated with varying concentrations of TGF-β, GDF5, or GDF6 for 14 days. Relative gene expression was normalized to mean housekeeping-gene expression and cells without growth-factor stimulation and plotted on a log scale. N = 3; data represent mean ± SEM. *P < 0.05.