(A-C) Embryos co-expressing the optogenetic module and Sqh::mCherry mounted with the ventral epithelium facing the objective were subjected to cycles of photo-activation of the cell base in the anterior (left) half of the embryo and confocal recording of the whole embryo. The experiment was started at the end of cellularization when initial accumulation of apical myosin-II was detected and terminated at different time points to record the plasma membrane signal (CIBN::GFP-pm) in the whole embryo using two-photon illumination. Still frames visualizing the plasma membrane (CIBN::GFP-pm) at a sub-apical plane at the initial time point of the experiment (A), 3 min (B) and 10 min (C) after initial photo-activation. 