Sdf-1 impact on embryonic stem cells. (A) Quantitative RT-PCR analysis of CXCR4 and CD9 mRNA in control and Sdf-1-treated embryonic stem cells (ESCs). (B) Western blotting analysis of CXCR4, CXCR7, CD9, and tubulin in control, Sdf-1-treated (Sdf-1), and either CXCR4 (siRNA CXCR4) or CXCR7 siRNA-treated (siRNA CXCR7) ESCs. (C) Migration of control or transfected with CXCR4 or CXCR7 siRNA ESCs in response to Sdf-1 gradient. (D) Proportion of hybrid myotubes formed in co-culture of C2C12 myoblasts and control or Sdf-1 pretreated ESCs. (E) Co-culture of C2C12 myoblasts (red) and control or Sdf-1 pretreated ESCs (green); nuclei, blue. Bar = 50 μm. CXCR, CXC chemokine receptor. *P <0.05. Error bars indicate standard deviation.