Gradients of Rac1 Nanoclusters Support Spatial Patterns of Rac1 Signaling

Abstract

Summary: Rac1 is a small RhoGTPase switch that orchestrates actin branching in space and time and protrusion/retraction cycles of the lamellipodia at the cell front during mesenchymal migration. Biosensor imaging has revealed a graded concentration of active GTP-loaded Rac1 in protruding regions of the cell. Here, using single-molecule imaging and super-resolution microscopy, we show an additional supramolecular organization of Rac1. We find that Rac1 partitions and is immobilized into nanoclusters of 50–100 molecules each. These nanoclusters assemble because of the interaction of the polybasic tail of Rac1 with the phosphoinositide lipids PIP2 and PIP3. The additional interactions with GEFs and possibly GAPs, downstream effectors, and other partners are responsible for an enrichment of Rac1 nanoclusters in protruding regions of the cell. Our results show that subcellular patterns of Rac1 activity are supported by gradients of signaling nanodomains of heterogeneous molecular composition, which presumably act as discrete signaling platforms. : Rac1 is a small GTPase protein controlling the polymerization of actin at the front of migrating cells. Using super-resolution microscopy, Remorino et al. show that Rac1 forms nanoclusters of heterogeneous composition, which presumably act as discrete signaling platforms. The subcellular distribution of Rac1 nanoclusters follows its pattern of activation. Keywords: Rac1, signaling, nanoclusters, cell polarity, single molecule, optogenetics