Comparison of V12-RacB protrusions to stress-induced blebs. (A and E) Cells were sealed between two coverslips in a Rose chamber and imaged at 1-min intervals. The cells stopped moving after 5 to 10 min in the sealed chamber and began to form blebs. Control cells before sealing (A) and after 20 min in the chamber (E) are shown. (B and F) V12-RacB (Ax4 parental) cells contained surface protrusions (B), but after treatment with 10 μM cytochalasin A for 5 min, the protrusions were lost from the surface (F). (C and G) Myosin null cells (mhcA) before sealing (C) and after a 20-min (G) or 1-h incubation. The cells did not show any blebbing after incubation (our unpublished results). (D and H) Expression of V12-RacB was induced for 3 days in JH10, a parental cell line of mhcA cells (D), and in mhcA cells (H). Surface protrusions were induced in both cell lines. Bar, 5 μm.