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Dictyostelium IQGAP-related protein specifically involved in the completion of cytokinesis.

Adachi H, Takahashi Y, Hasebe T, Shirouzu M, Yokoyama S, Sutoh K - J. Cell Biol. (1997)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153. f37771@m-unix.cc.u-tokyo.ac.jp

ABSTRACT
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.

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Growth of Dictyostelium cells in axenic suspension.  Wild-type AX2 and gapA− D42-2 cells were diluted in fresh medium at 105 cells per ml, and then shaken at 22°C and 150 rpm.  Their growth was monitored as the increase in cell number (A) or  turbidity (B; absorbance at 660 nm) with the same culture.
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Figure 7: Growth of Dictyostelium cells in axenic suspension. Wild-type AX2 and gapA− D42-2 cells were diluted in fresh medium at 105 cells per ml, and then shaken at 22°C and 150 rpm. Their growth was monitored as the increase in cell number (A) or turbidity (B; absorbance at 660 nm) with the same culture.

Mentions: To determine the step(s) at which GAPA acts during cytokinesis, the phenotype of gapA− cells was further characterized. First, the growth of gapA− cells in suspension culture was examined. It is known that Dictyostelium cells lacking myosin II grow as multinucleate cells on a substratum (De Lozanne and Spudich, 1987; Knecht and Loomis, 1987) like gapA− cells. In this case, the growth is not supported by “real” cytokinesis but by traction-mediated cytofission, which is dependent on the solid surface (Fukui et al., 1990), and the cells cannot survive in suspension culture. Unlike myosin II–deficient cells, gapA− cells grew in suspension culture (Fig. 7). The rate of increase in cell number was, however, much lower than that of the wildtype cells (Fig. 7 A). In contrast, the rates of increase in cell mass, monitored as the turbidity of the culture, were similar to each other (Fig. 7 B). Thus, the mutant strain also produced spherical giant cells in suspension culture (Fig. 2, B and F). These results suggest that, in the gapA− cells, cytokinesis was not completed at a considerable frequency.


Dictyostelium IQGAP-related protein specifically involved in the completion of cytokinesis.

Adachi H, Takahashi Y, Hasebe T, Shirouzu M, Yokoyama S, Sutoh K - J. Cell Biol. (1997)

Growth of Dictyostelium cells in axenic suspension.  Wild-type AX2 and gapA− D42-2 cells were diluted in fresh medium at 105 cells per ml, and then shaken at 22°C and 150 rpm.  Their growth was monitored as the increase in cell number (A) or  turbidity (B; absorbance at 660 nm) with the same culture.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139833&req=5

Figure 7: Growth of Dictyostelium cells in axenic suspension. Wild-type AX2 and gapA− D42-2 cells were diluted in fresh medium at 105 cells per ml, and then shaken at 22°C and 150 rpm. Their growth was monitored as the increase in cell number (A) or turbidity (B; absorbance at 660 nm) with the same culture.
Mentions: To determine the step(s) at which GAPA acts during cytokinesis, the phenotype of gapA− cells was further characterized. First, the growth of gapA− cells in suspension culture was examined. It is known that Dictyostelium cells lacking myosin II grow as multinucleate cells on a substratum (De Lozanne and Spudich, 1987; Knecht and Loomis, 1987) like gapA− cells. In this case, the growth is not supported by “real” cytokinesis but by traction-mediated cytofission, which is dependent on the solid surface (Fukui et al., 1990), and the cells cannot survive in suspension culture. Unlike myosin II–deficient cells, gapA− cells grew in suspension culture (Fig. 7). The rate of increase in cell number was, however, much lower than that of the wildtype cells (Fig. 7 A). In contrast, the rates of increase in cell mass, monitored as the turbidity of the culture, were similar to each other (Fig. 7 B). Thus, the mutant strain also produced spherical giant cells in suspension culture (Fig. 2, B and F). These results suggest that, in the gapA− cells, cytokinesis was not completed at a considerable frequency.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153. f37771@m-unix.cc.u-tokyo.ac.jp

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus