In vivo optochemical control of cell contractility at single-cell resolution.

The spatial and temporal dynamics of cell contractility plays a key role in tissue morphogenesis, wound healing, and cancer invasion. Here, we report a simple optochemical method to induce cell contractions in vivo during Drosophila morphogenesis at single-cell resolution. We employed the photolabile Ca2+ chelator o-nitrophenyl EGTA to induce bursts of intracellular free Ca2+ by laser photolysis in the epithelial tissue. Ca2+ bursts appear within seconds and are restricted to individual target cells. Cell contraction reliably followed within a minute, causing an approximately 50% drop in the cross-sectional area. Increased Ca2+ levels are reversible, and the target cells further participated in tissue morphogenesis. Depending on Rho kinase (ROCK) activity but not RhoGEF2, cell contractions are paralleled with non-muscle myosin II accumulation in the apico-medial cortex, indicating that Ca2+ bursts trigger non-muscle myosin II activation. Our approach can be, in principle, adapted to many experimental systems and species, as no specific genetic elements are required.