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J. Cell Biol.,
Volume 144, Number 2, January 25, 1999 305-313

* Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655; and We have investigated the role of the small
GTP-binding protein Rho in cytokinesis by microinjecting an inhibitor, C3 ribosyltransferase, into cultured
cells. Microinjection of C3 into prometaphase or metaphase normal rat kidney epithelial cells induced
immediate and global cortical movement of actin toward the metaphase plate, without an apparent effect
on the mitotic spindle. During anaphase, concentrated
cortical actin filaments migrated with separating 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 underwent
cleavage-like activities and most of them divided successfully. However, cytokinesis became abnormal, generating irregular ingressions and ectopic cleavage sites
even when mitosis was blocked with nocodazole. The
effects of C3 appeared to be dependent on cell adhesion; less adherent 3T3 fibroblasts 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
actin-myosin II interactions during cytokinesis, but regulates the spatial pattern of cortical activities and completion of cytokinesis possibly through modulating the mechanical strength of the cortex.
Institute of
Neurology, Department of Neurochemistry, University of London, London WC1N 1PJ, United Kingdom
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