Model. In WT embryos, Nuf promotes actin polymerization at the invaginating furrow by properly localizing RhoGEF2 to the furrow, where it activates Rho1. Up-regulating actin polymerization stabilizes furrow membrane. In nuf mutant embryos, failed RhoGEF2 recruitment results in insufficient actin polymerization. This in turn results in loss of furrow membrane integrity.