Relation between Sox2 expression levels and activin A:follistatin expression ratio in MPCs from different tissue sources. (a) Western blot analysis of Sox2 expression in BM-MPCs, T-MPCs, M-MPCs, and DP-MPCs before and after a 48-hour treatment with 10 ng/ml of activin A. (b) Activin A:follistatin expression ratio determined by quantitative RT-PCR in BM-MPCs before (day 0 (0)) and after their differentiation along chondrogenic, osteogenic, and adipogenic lineages. (c) mRNA expression levels of Sox2 in undifferentiated (day 0 (0)) and chondro-, osteo- and adipo-differentiated BM-MPCs. The values at day 0 (0) corresponding to the mRNA ratio of activin A:follistatin (b) to the mRNA level of Sox2 (c) relative to GAPDH were assigned the values of 100% ± SD. *P ≤ 0.05, versus Day 0.