Figure 2: Optogenetic upregulation and downregulation of cell contractility.

(a–f) Cells expressing optoGEF-RhoA and either CIBN-GFP-CAAX (a–c) or mito-CIBN-GFP (d–f) were locally and transiently activated. (a,d) Images of optoGEF-RhoA mCherry signal one minute before optogenetic activation. At time t=0, cells highlighted by blue squares (labelled 1 and 3) were illuminated, whereas cells highlighted by white squares (labelled 2 and 4) were not. (b) Traction forces exerted by cell clusters labelled 1 and 2 in a before and after optogenetic activation. (c) Tension within and between cells in clusters labelled 1 and 2 in a before and after optogenetic activation. (e) Traction forces exerted by clusters labelled 3 and 4 in d before and after optogenetic activation. (f) Tension within and between cells in clusters labelled 3 and 4 in d before and after optogenetic activation. For comparison, the vector difference of tractions and the scalar difference in tension between the two time points is shown on the right column of b,c and e,f. (g–l) Quantification of the mean traction amplitude over time for cells expressing CIBN-GFP-CAAX and optoGEF-RhoA (g,i,k) and for cells expressing optoGEF-RhoA and mito-CIBN-GFP (h,j,l) subjected to distinct illumination protocols. Thick lines display the means across different experiments and shaded areas indicate s.e.m. Black line in g corresponds to control cells expressing only CIBN-CAAX-GFP. Black line in h corresponds to control cells expressing mito-CIBN-GFP and CRY2-mCherry. (g,h) Activation for 5 min (one activation pulse every 10 s), in g, n_green=15 cells, n_black=9 cells, in h, n_red=8 cells, n_black=10 cells. (i,j) Activation for 40 min (one activation pulse every 30 s). In (i) n=9 cells; in j, n=7 cells. (k,l) Periodic activation separated by 20 min of recovery (with activation routines made of 2 pulses of blue light separated by 10 s). In k, n=6 cells; in l, n=10 cells. Scale bars, 20 μm.