ROCK and Rho will never Dia

Directional migration of a cell requires both lamellipodia formation at the leading edge and actomyosin contraction within the tail. New results from Tsuji et al. (page 819) indicate that Rho may mediate both tasks, and that these two arms of Rho signaling are antagonistic.

Rho signaling is known to mediate the formation of stress fibers, structures similar to actin bundles that are required for tail retraction. This function of Rho requires the effector kinase ROCK. The new results demonstrate that Rho can also signal through a different effector, mDia1, and cause membrane ruffling. The mDia1 pathway activated another Rho family GTPase member, Rac. In neuronal cells, Rho inhibits Rac, but this is the first demonstration that Rho can also activate Rac.

Tsuji et al. uncovered mDia1- mediated membrane ruffling by selectively inhibiting ROCK...