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© The Rockefeller University Press, 0021-9525/1997//891 $5.00
The Journal of Cell Biology, Volume 137, Number 4, , 1997 891-898

Article

Dictyostelium IQGAP-related Protein Specifically Involved in the Completion of Cytokinesis



Hiroyuki Adachi*, Yasuhiro Takahashi{ddagger}, Takeshi Hasebe{ddagger}, Mikako Shirouzu§, Shigeyuki Yokoyama§,||, and Kazuo Sutoh*

* Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153; {ddagger} Department of Applied Chemistry, Kogakuin University, Shinjuku-ku, Tokyo 163-91; § Cellular Signaling Laboratory, Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-01; and || Department of Biophysics and Biochemistry, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan

The gapA gene encoding a novel RasGTPase-activating protein (RasGAP)–related protein was found to be disrupted in a cytokinesis mutant of Dictyostelium that grows as giant and multinucleate cells in a dish culture. The predicted sequence of the GAPA protein showed considerable homology to those of Gap1/Sar1 from fission yeast and the COOH-terminal half of mammalian IQGAPs, the similarity extending beyond the RasGAP-related domain. In suspension culture, gapA– cells showed normal growth in terms of the increase in cell mass, but cytokinesis inefficiently occurred to produce spherical giant cells. Time-lapse recording of the dynamics of cell division in a dish culture revealed that, in the case of gapA– cells, cytokinesis was very frequently reversed at the step in which the midbody connecting the daughter cells should be severed. Earlier steps of cytokinesis in the gapA– cells seemed to be normal, since myosin II was accumulated at the cleavage furrow. Upon starvation, gapA– cells developed and formed fruiting bodies with viable spores, like the wild-type cells. These results indicate that the GAPA protein is specifically involved in the completion of cytokinesis. Recently, it was reported that IQGAPs are putative effectors for Rac and CDC42, members of the Rho family of GTPases, and participate in reorganization of the actin cytoskeleton. Thus, it is possible that Dictyostelium GAPA participates in the severing of the midbody by regulating the actin cytoskeleton through an interaction with a member of small GTPases.

1. Abbreviations used in this paper: GRD, GTPase-activating protein– related domain; RasGAP, RasGTPase-activating protein; REMI, restriction enzyme–mediated integration.

Please address all correspondence to Hiroyuki Adachi, Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153, Japan. Tel. and Fax: (81) 3-54546769. e-mail: f37771{at}m-unix.cc.u-tokyo.ac.jp


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