Movie 6.

Optogenetic disruption of F-actin in the flanking, non-constricting cells delays the transition from apical constriction to invagination. An embryo expressing the CIBN-pm and CRY2-mCherry-OCRL optogenetic constructs and the myosin marker, Sqh-mCherry, was stimulated on one side (adjacent to the constriction domain) during an early stage of apical constriction (right panel). A stage-matched, unstimulated embryo is shown on the left for comparison. Top: cross-section view; Bottom: ventral surface view. T = 00:00 (mm:ss) corresponds to the transition from apical constriction to invagination in control embryos.