H. Adachi et al., DICTYOSTELIUM IQGAP-RELATED PROTEIN SPECIFICALLY INVOLVED IN THE COMPLETION OF CYTOKINESIS, The Journal of cell biology, 137(4), 1997, pp. 891-898
The gapA gene encoding a novel RasGTPase-activating protein (RasGAP)-r
elated protein was found to be disrupted in a cytokinesis mutant of Di
ctyostelium that grows as giant and multinucleate cells in a dish cult
ure. The predicted sequence of the GAPA protein showed considerable ho
mology to those of Gap1/Sar1 from fission yeast and the COOH-terminal
half of mammalian IQGAPs, the similarity extending beyond the RasGAP-r
elated domain. In suspension culture, gapA(-) cells showed normal grow
th in terms of the increase in cell mass, but cytokinesis inefficientl
y occurred to produce spherical giant cells. Time-lapse recording of t
he dynamics of cell division in a dish culture revealed that, in the c
ase of gapA(-) cells, cytokinesis was very frequently reversed at the
step in which the midbody connecting the daughter cells should be seve
red. Earlier steps of cytokinesis in the gapA(-) cells seemed to be no
rmal, since myosin II was accumulated at the cleavage furrow. Upon sta
rvation, gnpA(-) cells developed and formed fruiting bodies with viabl
e spores, like the wild-type cells. These results indicate that the GA
PA protein is specifically involved in the completion of cytokinesis.
Recently, it was reported that IQGAPs are putative effecters for Rac a
nd CDC42, members of the Rho family of GTPases, and participate in reo
rganization of the actin cytoskeleton. Thus, it is possible that Dicty
ostelium GAPA participates in the severing of the midbody by regulatin
g the actin cytoskeleton through an interaction with a member of small
GTPases.