Fig. 1

Rac1 and Cdc42 activity gradients have different shapes. a FRET biosensors were used to monitor Rac1 (top) or Cdc42 (bottom) activity in freely migrating HeLa cells. GTPase activity is measured by the FRET ratio, and represented with a color scale. Several representative cells are shown. Scale bar: 20 µm. b Mean normalized FRET ratio of Rac1 (red) and Cdc42 (blue) is plotted as a function of the distance from the cell edge. The error bars indicate the standard deviation (s.d.) of n = 31 (Rac1) or n=19 (Cdc42) cells. Black segments at the top show positions at which the curves are statistically different (p < 0.05, Wilcoxon’s rank sum test). c Rho GTPase cycle, where the protein switches between an inactive and active state thanks to activators (GEFs) and deactivators (GAPs). d, e Two simplified mechanisms can explain the formation of cellular-scale Rho GTPase gradients. d A sharply localized GEF (blue profile) acts as a punctual source of active Rho GTPases (red) that are further transported by diffusion or flow (dashed gray arrows) until they reverse to the inactive state thanks to a GAP (black). e A cellular-scale distributed GEF locally activates the Rho GTPase such that both have the same profile