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dictyNews Volume 26 Number 12
dictyNews
Electronic Edition
Volume 26, number 12
April 28, 2006
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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The bundling activity of vasodilator-stimulated phosphoprotein is required
for filopodium formation
Antje Schirenbeck1, Rajesh Arasada1, Till Bretschneider2, Theresia E. B.
Stradal3, Michael Schleicher1, and Jan Faix4
1Cell Biology, Ludwig-Maximilians-University, Muenchen; 2 Cell Dynamics,
Max-Planck-Inst. f. Biochemistry Martinsried; 3 Signalling & Motil. Group,
German Research Centre f. Biotechnology, Braunschweig; 4 Inst. f.
Biophysical Chemistry, Hannover; Germany
Proc. Natl. Acad. Sci. USA, in press
Filopodia are highly dynamic finger-like cell protrusions filled with
parallel bundles of actin filaments. Previously we have shown that
Diaphanous-related formin dDia2 is involved in the formation of filopodia.
Another key player for the formation of filopodia across many species is
the vasodilator-stimulated phosphoprotein, VASP. It has been proposed that
the essential role of VASP for formation of filopodia is its competition
with capping proteins for filament barbed end interaction. In order to
better understand the function of VASP in filopodium formation, we analyzed
the in vitro and in vivo properties of Dictyostelium VASP (DdVASP) and
extended our findings to human VASP (HsVASP). Recombinant VASP from both
species nucleated and bundled actin filaments, but did neither compete with
capping proteins nor block depolymerization from barbed ends. Together with
the finding that DdVASP binds to the FH2 domain of dDia2, these data
indicate that the crucial role of VASP in filopodium formation is different
from uncapping of actin filaments. To identify the activity of DdVASP
required in this process, rescue experiments of DdVASP-null cells with
mutant DdVASP constructs were performed. Only wild-type (WT) DdVASP but not
a Änmutant lacking the F-actin bundling activity could rescue the ability
of these cells to form wild-type-like filopodia. Our data suggest that
DdVASP is complexed with dDia2 in filopodial tips and supports
formin-mediated filament elongation by bundling nascent actin filaments.
Submitted by: Michael Schleicher [schleicher@lrz.uni-muenchen.de]
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An Adhesion Molecule in Free-living Dictyostelium Amoebae with Integrin beta
Features
Sophie Cornillon, Leigh Gebbie, Mohammed Benghezal, Prashant Nair, Sebastien
Keller, Bernhard Wehrle-Haller, Steve J. Charette, Franz Brckert,
Franois Letourneur, Pierre Cosson
EMBO Reports, In press
The study of free-living amoebae has proven valuable to elucidate the
molecular mechanisms controlling phagocytosis, cell adhesion and motility.
In this study we identified a new adhesion molecule in Dictyostelium amoebae.
The SibA protein (Similar to Integrin Beta) is a type I transmembrane protein
and its cytosolic, transmembrane and extracellular domains contain features
also found in integrin beta chains. In addition, the conserved cytosolic
domain of SibA interacts with talin, a well-characterized partner of
mammalian integrins. Finally, genetic inactivation of SIBA affects adhesion
to phagocytic particles, as well as cell adhesion and spreading on its
substrate. It does not visibly alter the organization of the actin
cytoskeleton, cellular migration, or multicellular development. Our results
suggest that the SibA protein is a Dictyostelium cell adhesion molecule
presenting structural and functional similarities with metazoan integrin
beta chains. This study sheds light on the molecular mechanisms controlling
cell adhesion and their establishment during evolution.
Submitted by: Pierre Cosson [Pierre.Cosson@medecine.unige.ch]
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Naringenin is a novel inhibitor of Dictyostelium cell proliferation and cell
migration
Russ Misty, Raquel Martinez, Hind Ali and Paul A. Steimle,
Department of Biology, University of North Carolina at Greensboro,
Greensboro, NC 27402, USA
Biochemical Biophysical Research Communications, in press
(Available online 25 April 2006)
Naringenin is a flavanone compound that alters critical cellular processes
such as cell multiplication, glucose uptake, and mitochondrial activity. In
this study, we used the social amoeba, Dictyostelium discoideum, as a model
system for examining the cellular processes and signaling pathways affected
by naringenin. We found that naringenin inhibited Dictyostelium cell
division in a dose-dependent manner (IC50 20 M). Assays of Dictyostelium
chemotaxis and multicellular development revealed that naringenin possesses
a previously unrecognized ability to suppress amoeboid cell motility. We
also found that naringenin, which is known to inhibit phosphatidylinositol
3-kinase activity, had no apparent effect on phosphatidylinositol
3,4,5-trisphosphate synthesis in live Dictyostelium cells; suggesting that
this compound suppresses cell growth and migration via alternative signaling
pathways. In another context, the discoveries described here highlight the
value of using the Dictyostelium model system for identifying and
characterizing the mechanisms by which naringenin, and related compounds,
exert their effects on eukaryotic cells.
Submitted by: Paul Steimle [p_steiml@uncg.edu]
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First Among Equals: Competition Between Genetically Identical Cells
Anupama Khare and Gad Shaulsky
Department of Molecular and Human Genetics, Baylor College of Medicine,
One Baylor Plaza, Houston, TX 77030
Nature Reviews Genetics, in press
Competition between genetically identical organisms is considered
insignificant in evolutionary theory because it is presumed to have little
selective consequence. We argue that competition between genetically
identical cells could improve the fitness of a multicellular organism by
directing fitter cells to the germ-line or by eliminating unfit cells, and
that cell-competition mechanisms have been conserved in multicellular
organisms. We propose that competition between genetically identical or
highly similar units could have similar selective advantages at higher
organizational levels such as societies.
Submitted by: Gad Shaulsky [gadi@bcm.tmc.edu]
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[End dictyNews, volume 26, number 12] 
