Bleb-driven movement is induced by mechanical resistance. (A) Mechanical resistance provided by an overlay of 0.7% agarose induces a cell to move entirely in bleb mode. Blebs (dots) leave behind their cortical F-actin as a scar when they expand (see Video 4). (B) Blebs produced by a cell moving under a 0.7% agarose overlay containing fluorescent dye (0.5 mg/ml RITC-dextran) to reveal its outline. A bleb (dot) expands in less than 0.5 s, leaving behind an F-actin scar; it initially lacks an F-actin cortex, but rebuilds one in another second (see Video 6). (C) Cells embedded in 0.5% low melting-point agarose produce copious blebs. Ax2 cells used throughout, and expressing the F-actin reporter ABD-GFP in A and B. Bar, 10 µm.