Figure 8. Contractility independent increase in 2D migration is due to a concomitant decrease in integrin activation.

(a,b) Comparison of control (a) and treatment with 25 μM blebbistatin (b) on 2D collagen (50 μg ml⁻¹) shows a lack of activated β1 integrin clustering (green) compared with K20 anti-total β1 integrin antibody (red). (c) Addition of the activating β1 integrin antibody TS2/16 (2 μg ml⁻¹) to fibroblasts migrating across 2D globular collagen inhibits the increase in migration associated with 25 μM blebbistatin, N=3, n>80 (ANOVA). Errors bars: s.e.m. (d) Schematic summary of regulation by the 3D microenvironment of the dynamics of cell adhesions. The adhesion population consists of nascent (red) and mature adhesions, the latter comprised of retracting (green) intermediate (white), or stable (blue). As ECM fibre stiffness increases (bottom to top) the relative number of nascent and retracting adhesions are reduced, while highly stable adhesions are promoted. HR, LR and FB16 adhesion populations illustrate the actual calculated percentages for each condition. (e) Reducing the relative contractility of cells shifts the balance of nascent and retracting adhesions differently in soft (HR) and stiff (FB) ECMs, promoting further adhesion stability in the former. The critical balance threshold is shown in yellow. Arrows indicate change in the adhesion population above or below the threshold. (f) Schematic representation of the adhesion populations for cells within heterogeneous matrix of stiff fibrils (left) and homogeneous matrix of soft fibrils (right). Adhesion colour depicts the adhesion type shown in d. *Significantly different from all other conditions; P<0.05 (ANOVA). Scale bar, 10 μm.