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dictyNews Volume 19 Number 09
Dicty News
Electronic Edition
Volume 19, number 9
November 9, 2002
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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Requirement of a Vasodilator-stimulated Phosphoprotein (VASP) Family
Member for Cell Adhesion, the Formation of Filopodia, and Chemotaxis
in Dictyostelium
Young-Hoon Han1, Chang Y. Chung1, Deborah Wessels2, Stephen Stephens3,
Margaret A. Titus3, David R. Soll2, and Richard A. Firtel1,4
1Section of Cell and Developmental Biology
Division of Biological Sciences
Center for Molecular Genetics
University of California, San Diego
9500 Gilman Drive
La Jolla CA 92093-0634
2W.M. Keck Dynamic Image Analysis Facility
Department of Biological Sciences
University of Iowa
210 E Iowa Avenue
Iowa City IA 52242
3Department of Genetics, Cell Biology, and Development
University of Minnesota
6-160 Jackson Hall
321 Church Street S.E.
Minneapolis MN 56455
J. Biological Chemistry, in press.
SUMMARY
We have examined the function of a member of the vasodilator-stimulated
phosphoprotein family of proteins (DdVASP) in Dictyostelium. Ddvasp null
cells lack filopodia, whereas targeting DdVASP to the plasma membrane with
a myristoyl tag results in a significant increase in filopodia. The
PRD-EVH2 structure is required for both actin polymerization activity and
filopodia formation. Ddvasp null cells exhibit a chemotaxis defect, which
appears to be due to a defect in the ability of the cells to properly
adhere to the substratum and to suppress lateral pseudopod extension. We
demonstrate that during chemotaxis, the anterior ~50% of the cell lifts
from the substratum and remains elevated for up to a minute. These defects
lead to a significant decrease in chemotaxis efficiency. DdVASP localizes
to the leading edge in migrating cells and to the tips of filopodia. In
addition, Ddvasp null cells have a defect in particle adhesion but
internalize particles normally. Our results provide new insights into the
function of DdVASP in controlling the actin cytoskeleton during chemotaxis
and filopodia formation.
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Single-gene Greenbeard Effects in the Social Amoeba, Dictyostelium discoideum
David C. Queller1, Eleonora Ponte2, Salvatore Bozzaro2 and Joan E.Strassmann1
1 Dept. of Ecology and Evolution, MS-170, Rice University, P.O. Box 1892,
Houston, Texas 77251-1892 U.S.A.
2 Dept. Clinical and Biological Sciences, University of Turin, Ospedale S.
Luigi, 10043 Orbassano, Italy
Science in press
Abstract
Selection can favor reproductive altruism if an altruism allele aids copies
of itself by helping relatives. The alternative "greenbeard" mechanism, in
which an allele directly recognizes and aids copies of itself in others, is
generally thought to be too complex for a single gene to carry out. The csA
gene in Dictyostelium discoideum acts as a single-gene greenbeard. When
wildtype cells are mixed with csA knockout cells, the wildtype is more
altrustic, but is also able to preferentially direct the benefits to other
wildtype cells. Both properties derive directly from homophilic cell
adhesion of the protein encoded by csA.
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SadA, A Novel Adhesion Receptor In Dictyostelium
Petra Fey, Stephen Stephens*, Margaret A. Titus*, Rex L. Chisholm
Dept. of Cell and Molecular Biology, Northwestern University Feinberg School
of Medicine, Chicago, IL 60611
*Department of Genetics, Cell Biology and Development, University of Minnesota
321 Church St. S.E., 6-160 Jackson Hall, Minneapolis, MN 55455
J. Cell Biol., in press
Little is known about cell-substrate adhesion and how motile and adhesive
forces work together in moving cells. The ability to rapidly screen a large
number of insertional mutants prompted us to perform a genetic screen in
Dictyostelium to isolate adhesion deficient mutants. The resulting sad
(substrate adhesion deficient) mutants grew in plastic dishes without
attaching to the substrate. The cells were often larger than their wildtype
parents and displayed a rough surface with many apparent blebs. One of
these mutants, sadA-, completely lacked substrate adhesion in growth medium.
The sadA- mutant also showed slightly impaired cytokinesis, an aberrant
F-actin organization, and a phagocytosis defect. Deletion of the sadA gene
by homologous recombination recreated the original mutant phenotype.
Expression of sadA-GFP in sadA-null cells restored the wildtype phenotype.
In sadA-GFP rescued mutant cells, sadA-GFP localized to the cell surface,
appropriate for an adhesion molecule. SadA contains nine putative
transmembrane domains and three conserved EGF-like repeats in a predicted
extracellular domain. The EGF repeats are similar to corresponding regions
in proteins known to be involved in adhesion, such as tenascins and
integrins. Our data combined suggest that sadA is the first substrate
adhesion receptor to be identified in Dictyostelium.
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[End Dicty News, volume 19, number 9]
