Figure 9.

Schematic illustration of substrate contact dynamics in a moving fibroblast. (Top) Substrate contacts are initiated in the protruding and ruffling lamellipodium (Lam, ruf). Two classes of primary contacts are depicted: punctate focal complexes (fc) and linear contacts associated with some microspike bundles (ms/c). Their formation is associated with the activation of Rac and Cdc42, respectively. Each type of primary contact can develop into a precursor of a focal adhesion (pFA). Further abbreviations: iFA, intermediate focal adhesion in the body of the cell; tFA, focal adhesion at a trailing cell edge. (Bottom) Four types of contact sites with different strengths of anchorage to the substrate (anchors) are depicted and correspond to those in the upper diagram. All sites rely on contractility for their maintenance, indicated by different levels of myosin II–dependent tension (T and t). For precursor (pFA) and mature focal adhesions (iFA, tFA), myosin activation depends on Rho-kinase. The contractility of focal complexes is Rho-kinase independent. Microtubules (MT) interface with contact sites and modulate their turnover by locally inhibiting contractility. The relaxing dose is controlled by the total number and frequency of microtubule targeting events. Focal complexes may or may not be targeted by microtubules.