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dictyNews Volume 21 Number 07
Dicty News
Electronic Edition
Volume 21, number 7
September 5, 2003
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu.
Back issues of Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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Cell sorting by differential cell motility: a model for pattern formation
in Dictyostelium
Tamiki Umeda* and Kei Inouye#
*Department of Marine Engineering, Kobe University of Mercantile Marine,
Kobe 658-0022, Japan
#Department of Botany, Division of Biological Science, Graduate School of
Science, Kyoto University, Kyoto 606-8502, Japan
J. theor. Biol., in press
In the slug stage of the cellular slime mold Dictyostelium discoideum,
prespore cells and four types of prestalk cells show a well-defined spatial
distribution in a migrating slug. We have developed a continuous
mathematical model for the distribution pattern of these cell types based on
the balance of force in individual cells. In the model, cell types are
assumed to have different properties in cell motility, i.e., different
motive force, the rate of resistance against cell movement, and diffusion
coefficient. Analysis of the stationary solution of the model shows that
combination of these parameters and slug speed determines the 3-dimensional
shape of a slug and cell distribution pattern within it. Based on
experimental data of slug motive force and velocity measurements, appropriate
sets of parameters were chosen so that the cell-type distribution at
stationary state matches the distribution in real slugs. With these
parameters, we performed numerical calculation of the model in 2-dimensional
space using a moving particle method. The results reproduced many of the
basic features of slug morphogenesis, i.e., cell sorting, translocation
of the prestalk region, elongation of the slug, and its steady migration.
Submitted by: Kei Inouye [inoue@cosmos.bot.kyoto-u.ac.jp]
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Structure of the N-Terminal Domain of the Adenylyl Cyclase-Associated
Protein (CAP) from Dictyostelium discoideum
Dorota Ksiazek, Hans Brandstetter, Lars Israel, Gleb P. Bourenkov, Galina
Katchalova, Klaus-Peter Janssen, Hans D. Bartunik, Angelika A. Noegel,
Michael Schleicher and Tad A. Holak
Structure, in press
Cyclase-associated proteins (CAPs) are widely distributed and highly
conserved proteins that regulate actin remodeling in response to cellular
signals. The N-terminus of CAPs plays a role in Ras signaling and binds
adenylyl cyclase; the C-terminus binds to G-actin and thus alters the
dynamic rearrangements of the microfilament system. We report here the
X-ray structure of the N-terminal domain of the CAP from Dictyostelium
discoideum determined by a combination of single isomorphous replacement
with anomalous scattering (SIRAS) of iridium-soaked crystals. The overall
structure of this domain consists of an a-helix bundle composed of six
antiparallel helices and is found in the monomeric and Mg2+-induced dimeric
states. Together with gel filtration, cross-linking experiments, the
structural CAP adata suggest a multimeric state of the whole CAP molecule.
The presented structure is the first for an N-terminal domain of any CAP
and can be useful for defining specific functions for these domains.
Submitted by: Michael Schleicher [schleicher@lrz.uni-muenchen.de]
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Unique behavior and function of the mitochondrial ribosomal protein S4
(RPS4) in early Dictyostelium development
Koh-ichi Hosoya, Aiko Amagai, Junji Chida, and Yasuo Maeda*
Department of Developmental Biology and Neurosciences, Graduate School of
Life Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan
Zoological Science (in press)
Certain proteins encoded by mitochondrial DNA (mt-DNA), including
mt-ribosomal protein S4 (rps4), appear to play important roles in the
initiation of cell differentiation. Partial disruption of rps4 in
Dictyostelium discoideum Ax-2 cells by means of homologous recombination
greatly impairs the progression of differentiation, while the the rps4OE
cells in which the rps4 mRNA was overexpressed in the extra-mitochondrial
cytoplasm exhibit enhanced differentiation (Inazu et al., 1999). We have
prepared a specific anti-RPS4 antibody and generated transformants (rps4AS
cells) by antisense-mediated gene inactivation of rps4. Surprisingly, in the
rps4AS cells the progress of differentiation was found to be markedly
inhibited, suggesting that the antisense rps4 RNA synthesized in the
extra-mitochondrial cytoplasm might be as effective as the partial
disruption of rps4 gene. Immunostaining of the rps4OE cells with the
anti-RPS4 antibody demonstrated that the RPS4 protein synthesized in the
extra-mitochondrial cytoplasm is capable of moving to the nucleus, as
predicted by PSORTII. Taken together with the results obtained using
immunostained Ax-2 cells, we propose a possible pathway of RPS4
translocation coupled with differentiation.
Submitted by: Yasuo Maeda [ymaeda@mail.cc.tohoku.ac.jp]
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[End Dicty News, volume 21, number 7]
