Effect of chordin siRNA on cellular proliferation. Cellular proliferation was measured with the metabolic indicator WST-1 at the indicated periods after the start of culture. The cells were either not exposed to anything (Blank), to the transfection reagent Lipofectamine only (Lipo), or to the transfection reagent and a control siRNA (small interfering RNA) or chordin siRNA. The cells were then grown in osteogenic media for different periods. Each value is the mean ± standard deviation of three independent experiments. *P < 0.005 versus control siRNA.