Fig. 2.

Traction-force microscopy. (A) Actin and (B) focal adhesions in a U2OS cell visualized by GFP–actin and mApple–paxillin, respectively. The yellow dashed line in the actin image indicates the boundary between the lamellipodium and lamella, which contains transverse arcs and stress fibers. Whereas stress fibers are straight, peripheral bundles are invaginated as a result of the contractility within the cell body. Scale bar, 10 µm. (C) Forces exerted during traction-force microscopy. During traction-force microscopy, traction forces are reconstructed on the basis of substrate displacements that are tracked with fluorescent beads embedded in a soft elastic substrate. (D) Reconstructed traction stresses exerted on the underlying fibronectin-coated polyacrylamide substrate. Clearly, actin organization, the localization of adhesions marked by GFP–paxillin and the traction-force pattern show strong correlations with each other. In particular, regions of high forces correlate with the presence of focal adhesions.