Actin bending under load promotes branching in a forward direction. (A) Predicted architecture of branched actin networks depending on a mode of regulation. Combination of NPF targeting, barbed end capping, and curvature-dependent branching predicts optimal directionality of dendritic networks. (B) Actin filament bending creates binding sites for the Arp2/3 complex on the convex surface. (Left) Resistance of the load causes the actin filament to bend, thus creating a binding site (actin subunits outlined in red) for the Arp2/3 complex on the convex side. (Right) Activated Arp2/3 complex binds to the convex side of the mother filaments and nucleates a new branch toward the load.