Dynamic interactions between the cytoskeleton and integrins control cell adhesion, but regulatory mechanisms remain largely undefined. Here, we tested the extent to which the autoinhibitory head-tail interaction (HTI) in vinculin regulates formation and lifetime of the talin-vinculin complex, a proposed mediator of integrincytoskeleton bonds. In an ectopic recruitment assay, mutational reduction of HTI drove assembly of talin-vinculin complexes, whereas ectopic complexes did not form between talin and wild-type vinculin. Moreover, reduction of HTI altered the dynamic assembly of vinculin and talin in focal adhesions. Using fluorescence recovery after photobleaching, we show that the focal adhesion residency time of vinculin was enhanced up to 3-fold by HTI mutations. The slow dynamics of vinculin correlated with exposure of its cryptic talin-binding site, and a talin-binding site mutation rescued the dynamics of activated vinculin. Significantly, HTI-deficient vinculin inhibited the focal adhesion dynamics of talin, but not paxillin or ␣-actinin. These data show that talin conformation in cells permits vinculin binding, whereas the autoinhibited conformation of vinculin constitutes the barrier to complex formation. Down-regulation of HTI in vinculin to K d ϳ 10 ؊7 is sufficient to induce talin binding, and HTI is essential to the dynamics of vinculin and talin at focal adhesions. We therefore conclude that vinculin conformation, as modulated by the strength of HTI, directly regulates the formation and lifetime of talin-vinculin complexes in cells.Integrins mediate transmembrane connections between the actin cytoskeleton and extracellular matrix (1, 2). These connections are organized into discrete clusters such as focal complexes (3) and focal adhesions (3, 4) in adherent cells. Focal adhesions serve dual, opposing functions in cell motility, acting both in transmission of traction forces to generate displacement of the cell body and as anchors that resist detachment from the substratum (5). Thus, dynamic regulation of focal adhesion structure, and the integrin-cytoskeleton associations contained therein, plays a central role in balancing adhesive and migratory stimuli in the cell.Two key proteins implicated in the physical connections between integrins and F-actin are the actin-binding proteins talin and vinculin. In vitro, talin binds to  integrin tails through its FERM domain (6) and induces conformational changes in integrin associated with increased binding to the extracellular matrix (7). In cells, exposure of activated epitopes on  1 and  3 integrins and fibronectin binding are strongly inhibited by knockdown of talin expression (8). Moreover, talin-1 null cell lines are deficient in the formation of mechanical linkages between fibronectin,  3 integrin, and the cytoskeleton as shown by loss of a transient molecular slip bond that can sustain up to 2 piconewtons of force (9).Interestingly, the seminal report that talin binds directly to ␣ 5  1 integrin also demonstrated that integrin, talin, and vincu...
Background: Many cellular processes involve substantial shape changes. Traditional simulations of these cell shape changes require that grids and boundaries be moved as the cell's shape evolves. Here we demonstrate that accurate cell shape changes can be recreated using level set methods (LSM), in which the cellular shape is defined implicitly, thereby eschewing the need for updating boundaries.
We have proposed a model in which cells detect gradients of chemoattractant by balancing a fast local excitation and a slower global inhibition. To illustrate this general mechanism, we have developed an interactive applet that mimics laboratory experiments in which either spatially homogeneous or heterogeneous stimuli of chemoattractant are applied.
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