 (K) Quantification of the diameter of basal actomyosin rings in the non-activated region (NR, green) and activated region (AR, red) showing increased speed (4.8-fold change) and extent of ring constrictions in the photo-activated region (n= >41 cells). The ring diameter was normalized to the mean value of the first time point. The constriction speed was estimated by the slope of a fitted linear function to the data. (L) Light activation of the cell base resulted in a compaction of the tissue in the activated (AR) compared to the non-activated region (NR). Actomyosin rings were counted and normalized to the analyzed area to score ring density, which increased 1.35 times in the activated region after 5 min of photo-activation, showing that cells were still interconnected at the base and that photo-activation did not affect tissue integrity (N = 3 embryos; nNR: 431, nAR: 302). In each box plot, the central mark, the bottom, and the top edge of each box indicates the median, the 25th and 75th percentile, respectively. Whiskers extent to the most extreme data point 