The GxcM-Fbp17/RacC-WASP signaling cascade in the formation of a rear cortical subcompartment. GxcM, which localizes selectively in the rear of Dictyostelium cells, signals through Fbp17 and RacC to activate WASP by releasing its VCA tail, which in turn promotes Arp2/3 complex-mediated cortical actin assembly. Over-activation of the signaling cascade triggers excessive actin polymerization in the rear, whereas disruption of the cascade leads to defects in cortical rigidity and function.