Embryos expressing RhoGEF2-CRY2/CIBN::GFPpm and the membrane marker GAP43::mCherry were mounted with the ventral epithelium facing the objective. To analyze apical dynamics at each activation cycle, the photo-activation time was limited to ~ 20 s and was followed by the acquisition of a 5 µm-sized apical image stack resulting in a total time resolution of 35 s. The basal surface of the anterior (left) half of the embryo was photo-activated. (F,G) Graphs showing the average apical area (F) and anisotropy (G) of cells in the non-activated region (green), in the activated region that constricted (purple) and that did not constrict (red). The straight line indicates the mean value at a given time-point, the semi-transparent colored area indicated the respective standard deviation. Cells in the non-activated region constricted efficiently and progressively acquired anisotropy. Constricting cells in the activated region constricted slower in an isotropic manner. Non-constricting cells in the activated region did not show net decrease in apical area and gain of anisotropy (nNR = 34, nAR, non-con. = 20, nAR, con = 59). 