Jurkat T cells were transfected with control or FIP3.1 siRNA, then transfected again with empty vector or with expression vectors encoding Myc-tagged-Rac1WT, -Rac1G12V (constitutively active mutant), or -Rac1Rac1T17N (dominant negative mutant). Cells were allowed to spread on poly-lysine-coated coverslips for the indicated time and the spreading area of cells measured. A-C, H: Population analyses of the spreading area of cells at the level of the contact surface. A-C: Time course plots representing the mean ± SEM of the data shown as in I. D-G: Staining for nucleus (blue = Dapi), F-actin (green = phalloidin) and Rac1-Myc (red = anti-Myc) is shown. A single optical section at the level of the contact surface is shown. Bar, 5 µm. 