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]