Figure 3. Establishment of polarity by Rac/Rho.

(A) The small GTPases Rac and Rho (or at least their best studied representatives in mammals, Rac1 and RhoA) ultimately control different migration modes, i.e. mesenchymal migration by Rac and amoeboid migration by Rho. During mesenchymal migration, Rac activity dominates at the leading edge (yellow), while Rho signaling is enhanced toward the cell rear (blue), leading to the formation of a lamellipodium at the leading edge. (B) Amoeboid movement is characterized by high levels of active Rho and decreased Rac signaling, causing elevated contractility giving rise to plasma membrane blebbing. (C) Rac and Rho signaling displays a mutual antagonism at multiple levels. For details see text.