Graf^CR57/Graf^CR57 embryos do not show the polygonal F-actin organization in early stages of cellularization; instead there is premature contractile ring formation during early cellularization and enhanced ring constriction in mid and late cellularization, with the nuclei displaying a bottleneck appearance. Laser ablation experiments show increased contractile ring tension/contractility (increased displacement and initial recoil velocity). The slow phase of furrow extension is extended and the fast phase starts at a later time point.