dictyNews
Electronic Edition
Volume 39, number 8
March 15, 2013
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Abstracts
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Phase geometries of two-dimensional excitable waves govern
self-organized morphodynamics of amoeboid cells.
Daisuke Taniguchi‡ ,Shuji Ishihara‡ , Takehiko Oonuki, Mai
Honda-Kitahara, Kunihiko Kaneko, and Satoshi Sawai
(‡ equal contribution)
1. Graduate School of Arts and Sciences, and
2. Research Center for Complex Systems Biology, University of
Tokyo, Meguro-ku, Tokyo 153-8902, Japan;
3. Precursory Research for Embryonic Science and Technology
(PRESTO), JST, Kawaguchi, Saitama 332-0012, Japan
PNAS, in press
In both randomly moving Dictyostelium and mammalian cells,
phosphatidylinositol (3,4,5)-trisphosphate and F-actin are known to
propagate as waves at the membrane and act to push out the
protruding edge. To date, however, the relationship between the
wave geometry and the patterns of amoeboid shape change remains
elusive. Here, by using phase map analysis, we show that morphology
dynamics of randomly moving Dictyostelium discoideum cells can be
characterized by the number, topology, and position of spatial phase
singularities, i.e., points that represent organizing centers of rotating
waves. A single isolated singularity near the cellular edge induced a
rotational protrusion, whereas a pair of singularities supported a
symmetric extension. These singularities appeared by strong phase
resetting due to de novo nucleation at the back of preexisting waves.
Analysis of a theoretical model indicated excitability of the system that
is governed by positive feedback from phosphatidylinositol
(3,4,5)-trisphosphate to PI3-kinase activation, and we showed
experimentally that this requires F-actin. Furthermore, by incorporating
membrane deformation into the model, we demonstrated that
geometries of competing waves explain most of the observed
semiperiodic changes in amoeboid morphology.
Submitted by Satoshi Sawai [[log in to unmask]]
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The Dictyostelium prestalk inducer DIF-1 directs phosphorylation
of a bZIP transcription factor
Yoko Yamada, Yuzuru Kubohara1, Haruhisa Kikuchi2, Yoshiteru
Oshima2, Hong Yu Wang, Susan Ross and Jeffrey G. Williams*
College of Life Sciences, Welcome Trust Biocentre,University of
Dundee, Dow St., Dundee, DD1 5EH, UK
1 Department of Molecular and Cellular Biology, Institute for
Molecular and Cellular Regulation, Gunma University,
Maebashi 371-8512, Japan
2 Laboratory of Natural Product Chemistry, Tohoku University
Graduate School of Pharmaceutical Sciences, Aoba-yama,
Aoba-ku, Sendai 980-8578, Japan
Int J Dev Biol, in press
Background DIF-1, a chlorinated hexaphenone produced by developing
Dictyostelium cells, induces prestalk differentiation. DimB is a bZIP
transcription factor that accumulates in the nucleus upon exposure to
DIF-1, where it directly activates transcription of DIF-responsive genes.
The signaling steps upstream of DimB and downstream of DIF-1 are
entirely unknown. Results Analysis by mass spectrometry shows that
incubation with DIF-1 rapidly stimulates phosphorylation at several sites
in DimB. We characterize the most highly responsive site, S590, which
is located very close to the C terminus. A point mutation in this site,
S590A, does not inhibit DimB nuclear accumulation in response to DIF.
However, this seems likely to reflect functional redundancy with other
sites; because a panel of chemical variants on the structure of DIF-1
show a correlation between their potencies as inducers of DimB nuclear
accumulation and their potencies as inducers of phosphorylation at S590.
Furthermore the S590A mutant is fully active in mutant rescue of a dimB
null strain, arguing against an alternative role in transcriptional activation
of target genes. Conclusions i) DIF-1 directs phosphorylation at S590 ii)
although it is not essential for nuclear accumulation in response to DIF-1
correlative evidence, based upon a panel of DIF-1 related molecules,
suggests that this modification may play a redundant role in the process
iii) We also present evidence that the kinase activity, which phosphorylates
S590, is non-nuclear and that this signalling pathway is, in part at least,
independent of the DIF-regulated STATc activation pathway.
Submitted by Jeff Williams [[log in to unmask]]
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[End dictyNews, volume 39, number 8]
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