Fig. 8. Stretching of substrata induces actin polymerization at peripheral FAs in cells in which myosin II is inhibited. Cells grown on an FN-coated elastic substratum were treated with 100 µM blebbistatin for 30 minutes and then the substratum was uniaxially stretched, as in Fig. 7. (A-D) Alexa568-actin (B,D) was introduced into cells with (C,D) or without (A,B) stretching of the substratum. The cells were stained for ₅ integrin (A,C). (D) Arrows indicate actin incorporated at peripheral FAs. Double-headed arrow indicates the direction of the stretch axis. (C) Red arrows indicate the central ₅-integrin clusters that are not associated with actin incorporation. (E-I) Alexa568-actin was introduced into cells with stretching of the substratum (F,H, green in I). The cells were stained for F-actin (E,G, red in I). The boxed area in E is shown at higher magnification in G-I: actin was incorporated along F-actin bundles near their ends. (E) Actin was incorporated along F-actin bundles oriented parallel to the stretch axis (cell 1) but was not along the bundles oriented with large angles to the axis (cell 2). Folds perpendicular to the stretch axis were generated as in Fig. 7. Scale bars: 20 µm (A-F); 10 µm (G-I). (J) The fluorescence intensity of Alexa568-actin near the end of an F-actin bundle was plotted against the angle of the bundle to the stretch axis. The fluorescence intensities within 6 µm along the F-actin bundle from its tip were measured and normalized with respect to the maximum value. A total of 123 F-actin bundles in 34 cells were plotted. The red line represents the linear fitting. CC, correlation coefficient.