Figure 4: Changes in contractility are paralleled by tissue deformation.

(a,b) Overlays of two consecutive images of myr-iRFP separated by 40 s (in green first image, in purple second image) before (a) and after (b) local activation (blue rectangle, one pulse every 20 s for 5 min) of the optoGEF-RhoA/CIBN-GFP-CAAX system. Zooms of the area in the black rectangle are represented at the bottom of the panel. (c,d) Histograms of cell edge velocity before (c) and just after (d) activation. Velocities outside the activation zone are represented in black whereas those in the activation zone are represented in red. Histograms are obtained by averaging 48 velocity fields obtained by PIV analysis. Bottom: representation of the median velocity fields over the 48 experiments. (e) Time evolution of membrane velocity magnitude averaged over the 48 experiments. (f,g) Bright-field images before (f) and after (g) local activation (blue rectangle) of the optoGEF-RhoA/mito-CIBN-GFP system. Activation was performed every 40 s for 5 min. (h,i) Histograms of velocity fields before (h) and after (i) the start of contractility relaxation. Velocities outside the activation zone are represented in black and those inside the activation zone are represented in red. Histograms were obtained by averaging 22 velocity fields obtained by PIV analysis on bright-field images. Bottom: representation of the median velocity vectors over the 22 experiments. (j) Time evolution of velocity magnitude fields averaged over the 22 experiments. Scale bars, 20 μm.