Optogenetic dissection of Rac1 and Cdc42 gradient shaping

Abstract

During migration, cells present a polarized activity that is aligned with the direction of motion. This cell polarity is established by an internal molecular circuitry, without the requirement of extracellular cues. At the heart of this circuitry, Rho GTPases spontaneously form spatial gradients that define the front and back of migrating cells. At the front of the cell, active Cdc42 forms a steep gradient whereas active Rac1 forms a more extended pattern peaking a few microns away from the cell tip. What are the mechanisms shaping these gradients, and what is the functional role of the shape of these gradients? Combining optogenetics and cell micopatterning, we show that Cdc42 and Rac1 gradients are set by spatial patterns of activators and deactivators and not directly by advection or diffusion mechanisms. Cdc42 simply follows the distribution of GEFs thanks to a uniform GAP activity, whereas Rac1 shaping requires the activity of an additional GAP, β2-chimaerin, which is sharply localized at the tip of the cell. We find that β2-chimaerin recruitment depends on feedbacks from Cdc42 and Rac1. Functionally, the extent -neither the slope nor the amplitude-of RhoGTPases gradients governs cell migration. A Cdc42 gradient with a short spatial extent is required to maximize directionality during cell migration while an extended Rac1 gradient controls the speed of the cell.

A novel interplay between GEFs orchestrates Cdc42 activity during cell polarity and cytokinesis

“…Cdc42 and Rac are activated by similar pathways and share the same effectors. Several recent experiments indicate that actin cytoskeleton reorganization leading to cell migration occurs in a biphasic manner, where Cdc42 activation at new sites sets the direction, while robust Rac activation determines the speed (de Beco et al, 2018;Yang et al, 2016). Unlike most eukaryotes, the genome of S. pombe does not contain a Rac GTPase.…”

“…In certain mammalian cells, Cdc42 and Rac1 appear to activate cell growth in a biphasic manner (de Beco et al, 2018;Yang et al, 2016). For example, during motility, the GTPases, Rho, Rac, and Cdc42, regulate the actin cytoskeleton (Heasman and Ridley, 2008;Machacek et al, 2009).…”