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. ============= Abstracts ============= 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- [End Dicty News, volume 19, number 9]