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Vol. 17, Issue 1, 43-55, January 2006
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* Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4256;
Department of Biological Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
Submitted June 27, 2005;
Accepted October 12, 2005
Monitoring Editor: David Drubin
In anaphase, microtubules provide a specification signal for positioning of the contractile ring. However, the nature of the signal remains unknown. The small GTPase Rho is a potent regulator of cytokinesis, but the involvement of Rho in contractile ring formation is disputed. Here, we show that Rho serves as a microtubule-dependent signal that specifies the position of the contractile ring. We found that Rho translocates to the equatorial region before furrow ingression. The Rho-specific inhibitor C3 exoenzyme and small interfering RNA to the Rho GDP/GTP exchange factor ECT2 prevent this translocation and disrupt contractile ring formation, indicating that active Rho is required for contractile ring formation. ECT2 forms a complex with the GTPase-activating protein MgcRacGAP and the kinesinlike protein MKLP1 at the central spindle, and the localization of ECT2 at the central spindle depends on MgcRacGAP and MKLP1. In addition, we show that the bundled microtubules direct Rho-mediated signaling molecules to the furrowing site and regulate furrow formation. Our study provides strong evidence for the requirement of Rho-mediated signaling in contractile ring formation.
Abbreviations used: C3, C3 exoenzyme; GAP, GTPase-activating protein; GEF, GDP/GTP exchange factor; GFP, green fluorescent protein; MRLC, myosin regulatory light chain; PAV, Pavarotti; PBL, Pebble; RNAi, RNA interference; siRNA, small interfering RNA; TCA, trichloroacetic acid.
The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).
Present address: Division of Microbiology and Oral Infection, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8588, Japan
Present address: Lipid Biology Laboratory, RIKEN Discovery Research Institute, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
|| Present address: Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709-2233
¶ Present address: Laboratory of Functional Genomics, Korea Institute of Radiological and Medical Sciences, Seoul 139-706, Korea.
Address correspondence to: Keiju Kamijo (kkamijo{at}ja3.so-net.ne.jp).
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