The small GTP-binding protein Rho regulates cortical activities in cultured cells during division

We have investigated the role of the small GTP-binding protein Rho in cytok inesis by microinjecting an inhibitor, C3 ribosyltransferase, into cultured cells. Microinjection of C3 into prometaphase or metaphase normal rat kidn ey epithelial cells induced immediate and global cortical movement of actin toward the metaphase plate, without an apparent effect on the mitotic spin dle. During anaphase, concentrated cortical actin filaments migrated with s eparating chromosomes, leaving no apparent concentration of actin filaments along the equator. Myosin II in injected epithelial cells showed a diffuse distribution throughout cell division. All treated, well-adherent cells un derwent cleavage-like activities and most of them divided successfully. How ever, cytokinesis became abnormal, generating irregular ingressions and ect opic cleavage sites even when mitosis was blocked with nocodazole, The effe cts of C3 appeared to be dependent on cell adhesion; less adherent 3T3 fibr oblasts exhibited irregular cortical ingression only when cells started to increase attachment during respreading, but managed to complete cytokinesis . Poorly adherent HeLa cells showed neither ectopic cleavage nor completion of cytokinesis, Our results indicate that Rho does not simply activate act in-myosin II interactions during cytokinesis, but regulates the spatial pat tern of cortical activities and completion of cytokinesis possibly through modulating the mechanical strength of the cortex.