eLife assessment
This important study combines experiments with optogenetic actuation and theory to understand how signalling proteins control the switch between cell protrusion and retraction, two processes in single-cell migration. The authors examine the role of a guanine exchange factor (GEF) on the downstream effectors RhoA and Cdc42, which trigger retraction and protrusion, respectively. The experimental and theoretical evidence provides a convincing explanation for why and how a single signalling protein – here, a GEF of RhoA – can control both protrusion and retraction.