Depletion of Dlg1 delays the transition from apical constriction to invagination (surface view). Wild type embryo (left) and dlg1 RNAi embryo (right) undergo apical constriction at a similar rate. However, the transition to invagination is delayed in the dlg1 RNAi embryo. Note that the apical domain of the flanking, non-constricting cells adjacent to the constriction domain are over-stretched in the dlg1 RNAi embryo. Cell membranes are labeled with E-cadherin-GFP. T = 00:00 (mm:ss) marks the onset of gastrulation.