Rho family GTPases bring a familiar ring to cell wound repair

Abstract

Repair of wounds to single cells involves dynamic membrane and cytoskeletal rearrangements necessary to seal the wound and repair the underlying cytoskeleton cortex. One group of proteins essential to the cortical remodeling is the Rho family of small GTPases. Recently we showed that the founding members of this GTPases family, Rho, Rac, and Cdc42, are all essential for normal single cell wound repair and accumulate at the wound periphery in distinct temporal/spatial patterns in the Drosophila cell wound model. In addition, these proteins communicate with one another and with the cytoskeleton to regulate their distribution in response to wounds. Unexpectedly, we found evidence for context specific Rho GTPase binding to downstream targets or "effectors" which cannot be explained solely by means of local GTPase activation. Here we discuss these observations in relation to similar studies in single cell wound repair in the Xenopus oocyte, and highlight how these cell wound models serve as powerful tools to understand both cell wound repair and Rho GTPase biology.

Keywords: Cdc42; Drosophila; GAPs, GTPase activating proteins; GDIs, guanine nucleotide dissociation inhibitors; GEFs, guanine nucleotide exchange factors; RBD, Rho Binding Domain; Rac; Rho; Rho family GTPases; Xenopus.; cell wound repair; cytoskeleton.

Figure 1.

Mechanisms of single cell repair. (A) Schematic depicting single cell repair mechanisms including vesicle fusion and cortical cytoskeleton remodeling by cortical flow and actomyosin contraction. While XY views depict the overall repair process, a 'behind the scenes' account of processes such as vesicles trafficking toward the wound from an internal membrane source are visible in XZ views (black arrow). Arrows (blue) in XY and XZ views show cortical flow as polarized trafficking of actin and myosin toward the wound. (B-D) Fluorescent micrographs of actomyosin contraction (B and C) or cortical flow (D and E) in single cell repair. An actomyosin array is formed at the wound edge in the Xenopus oocyte ((B) © 2001 Rockefeller University Press. Originally published in Journal of Cell Biology 154: 785–797) and the Drosophila syncytial embryo (C). Cortical flow of actin contributes to cortical remodeling in Xenopus (D; © 2005 Rockefeller University Press. Originally published in Journal of Cell Biology 168: 429–439) and Drosophila (E) single cell repair.

Figure 2.

GTPase arrays form in response to cell wound repair the Xenopus oocyte and Drosophila syncytial embryo cell repair models. (A, D, and E) Fluorescent reporters for Xenopus studies use biosensor reporters depicting activated Rho family GTPases. (B, C, F, and G) Drosophila Rho GTPase fluorescent probes report all protein (not just the activated forms). (A) Activated RhoA and Cdc42 form non-overlapping concentric rings in the Xenopus oocyte (© 2005 Rockefeller University Press. Originally published in Journal of Cell Biology 168: 429–439). (B) Rho1 and Cdc42 form overlapping arrays in the Drosophila syncytial embryo with the Rho1 array interior to Cdc42. (C) Rac1 and Rho1 form overlapping arrays in the Drosophila syncytial embryo with the Rho1 array interior to Rac1. (D and E) RhoA and Cdc42 arrays in the Xenopus model translocate upon inhibition of contraction with the Rok inhibitor Y27632 (adapted from and reproduced with permission from Elsevier). (F and G) Rho1 and Cdc42 arrays in the Drosophila model are unable to translocate when contraction is inhibited with Y27632 (wound edge outlined in red). (H) Schematic depicting the relative localization of Rho family GTPases in the Xenopus and Drosophila single cell wound repair models (adapted from and reproduced with permission from Elsevier).