Fig. 3. Inhibition of Ras but not Rac reduces PtdIns(3,4,5)P₃ production at the leading edge of lamellipodia. (A,B) MTLn3 cells were transfected with control or Rac1 siRNA. (A) Representative images of control siRNA or Rac1 siRNA-treated cells stimulated with EGF for 3 minutes and stained with anti-PtdIns(3,4,5)P₃ antibody are shown. (B) Quantification of leading-edge PtdIns(3,4,5)P₃ in siRNA-treated cells. The data are mean ± s.e.m. from four experiments. Bar, 10 µm in all panels. (C,D) MTLn3 cells were transfected with control siRNA or pools of four siRNA duplexes specific for H-Ras, K-Ras or N-Ras. (C) Representative images of control siRNA or K-Ras siRNA-treated cells stimulated with EGF for 0, 1 or 3 minutes and stained with anti-PtdIns(3,4,5)P₃ antibody are shown. (D) Quantification of leading-edge PtdIns(3,4,5)P₃ in siRNA-treated cells. The data are mean ± s.e.m. from 40 cells per condition, and are representative of two independent experiments.