Kinetic Control of Out-Of-Equilibrium Dynamics in the RhoA Signaling Cascade Shapes Actomyosin Contractility

Cellular functions rely on the precise timing of signal transmission through sequential activation cascades, yet the origin and functional role of signaling delays remain poorly understood. Here, we dissect the temporal organization of the RhoA signaling cascade during pulsed actomyosin contractility in the early C. elegans embryo. We uncover a stereotypical delay between upstream RhoA/ROCK activation and downstream myosin II recruitment. Using TIRF single-molecule microscopy, we show that this delay arises from binding and unbinding kinetics of myosin rather than from slow biochemical reactions. A simple and versatile kinetic model parameterized by these measurements accurately predicts the temporal evolution of myosin accumulation and reveals active control of the dynamic range of the cascade. Perturbing actin and myosin turnover experimentally confirms these predictions, and numerical simulations show that the delay between actin and myosin plays a critical role in force deployment during pulsed contraction. Together, our results indicate that kinetic delays in signaling cascades are not simply tolerated during morphogenesis, but actively shape force deployment in the cell.