Figure 6.
(A and B) Microinjection of Tβ4 into GFP-α-actinin–expressing Swiss 3T3 fibroblasts causes dramatic disassembly of actin filament bundles (A, before microinjection, indicated by thin arrows; B, 1 min after microinjection). Note that the actin cytoskeleton remains unaltered in the noninjected neighboring cell (indicated by thick arrow). (C and D) Control experiments: besides negligible membrane damage at the site of microinjection, the overall integrity of the actin cytoskeleton (C) is maintained after microinjection of PBS (D). The fluorescent images were obtained with a 100× objective. (E and F) Contractility of Swiss 3T3 fibroblasts, as judged by the strength of the cell-induced wrinkles on the silicone substrate (indicated by an arrow in E), is reduced within 1 min of microinjection of Tβ4 (F, note the disappearance of the wrinkles). (G and H) Control experiment: microinjection of PBS does not cause any change in the cellular contractility (G and H refer to before and after microinjection of PBS, respectively). These phase–contrast images were acquired using a 40× objective.