eLife Assessment
This study provides direct and compelling evidence that lamellipodial protrusions dynamically adjust Arp2/3 complex incorporation in response to mechanical counterforces, while also modulating cellular responsiveness to upstream signals like Rac GTPase. By combining endogenous labeling, live-cell imaging, and optogenetic signaling activation, the work demonstrates how adhesion state and physicochemical perturbations reproducibly alter branched actin organization, offering a fundamental advance over previous works. The findings deliver significant insights that will resonate broadly with cell biologists and biochemists studying actin dynamics and mechanotransduction.