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. ============= Abstracts ============= 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] ----------------------------------------------------------------------------- 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 BrŸckert, 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] ----------------------------------------------------------------------------- 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] ----------------------------------------------------------------------------- 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] ============================================================================== [End dictyNews, volume 26, number 12]