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© The Rockefeller University Press, 0021-9525/1998//483 $5.00
The Journal of Cell Biology, Volume 141, Number 2, , 1998 483-492

Articles

A Role for Dictyostelium RacE in Cortical Tension and Cleavage Furrow Progression



Noel Gerald*, Jianwu Dai*, H. Ping Ting-Beall{ddagger}, and Arturo De Lozanne*

* Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710; and {ddagger} Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708

The small GTPase racE is essential for cytokinesis in Dictyostelium. We found that this requirement is restricted to cells grown in suspension. When attached to a substrate, racE null cells form an actomyosin contractile ring and complete cytokinesis normally. Nonetheless, racE null cells fail completely in cytokinesis when in suspension. To understand this conditional requirement for racE, we developed a method to observe cytokinesis in suspension. Using this approach, we found that racE null cells attempt cytokinesis in suspension by forming a contractile ring and cleavage furrow. However, the cells form multiple blebs and fail in cytokinesis by regression of the cleavage furrow. We believe this phenotype is caused by the extremely low level of cortical tension found in racE null cells compared to wild-type cells. The reduced cortical tension of racE null cells is not caused by a decrease in their content of F-actin. Instead, mitotic racE null cells contain abnormal F-actin aggregates. These results suggest that racE is essential for the organization of the cortical cytoskeleton to maintain proper cortical integrity. This function of racE is independent of attachment to a substrate, but can be bypassed by other signaling pathways induced by adhesion to a substrate.

Abbreviations used in this paper: DAPI, 4,6-diamindino-2-phenylindole; DIC, differential interference contrast; GFP, green fluorescent protein; MHC, myosin II heavy chain.

Address all correspondence to Arturo De Lozanne, Department of Cell Biology, Box 3709, Duke University Medical Center, Durham, NC 27710. Tel.: (919) 681-6851. Fax: (919) 681-7978. E-mail: a.delozanne{at}cellbio.duke.edu


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