YY1 associates with HDAC9c to govern MSC osteogenic differentiation. (A) Western blot analysis of YY1 knockdown efficiency by shControl, shYY1-A1, shYY1-B1, shYY1-C1, shYY1-D1, or shYY1-E1 in hMSCs. (B) After infection, hMSCs were incubated in osteogenic differentiation media for 7 days and stained with Alizarin Red S. (C) Western blot analysis of YY1 expression in undifferentiated MSCs and primary bone cells. β-Actin served as the control. (D, E) Relative mRNA (D) and protein expression (E) of p38 in osteoblasts infected with two specific YY1 shRNA by qRT-PCR and western blot, respectively. (F) Western blot analysis of YY1 and HDAC9c expression in hMSCs and differentiated osteoblasts. (G) Cell extracts were harvested after induction of osteoblast differentiation of MSCs for 7 days and subjected to immunoprecipitation (IP) with YY1 antibody followed by Western blot analysis with the indicated antibodies. (H) Cells extracts from osteoblasts were immunoprecipitated with different amount of YY1 antibody and subjected to Western blot analysis with the indicated antibodies. Error bars represent ± SD. *P < 0.05 and ***P < 0.001, Student’s t-test.