dictyNews Electronic Edition Volume 37, number 4 August 12, 2011 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. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= Salmonella typhimurium is pathogenic for Dictyostelium cells and subverts the starvation response Alessio Sillo*1, Jan Matthias#1, Roman Konertz#, Salvatore Bozzaro*2 and Ludwig Eichinger#2¤ *Department of Clinical and Biological Sciences, University of Turin, AOU S. Luigi, 10043 Orbassano (Torino), Italy #Center for Biochemistry, Medical Faculty, University of Cologne, Joseph-Stelzmann-Str. 52, D-50931 Cologne (Germany) Cell. Microbiol., in press In unicellular amoebae, such as Dictyostelium discoideum, bacterial phagocytosis is a food hunting device, while in higher organisms it is the first defence barrier against microbial infection. In both cases, pathogenic bacteria exploit phagocytosis to enter the cell and multiply intracellularly. Salmonella typhimurium, the agent of food-borne gastroenteritis, is phagocytosed by both macrophages and Dictyostelium cells. By using cell biological assays and global transcriptional analysis with DNA microarrays covering the Dictyostelium genome, we show here that S. typhimurium is pathogenic for Dictyostelium cells. Depending on the degree of virulence, which in turn depended on bacterial growth conditions, Salmonella could kill Dictyostelium cells or inhibit their growth and development. In the early phase of infection in non-nutrient buffer, the ingested bacteria escaped degradation, induced a starvation-like transcriptional response but inhibited selectively genes required for chemotaxis and aggregation. This way differentiation of the host cells into spore and stalk cells was blocked or delayed, which in turn is likely to be favourable for the establishment of a replicative niche for Salmonella. Inhibition of the aggregation competence and chemotactic streaming of aggregation-competent cells in the presence of Salmonella suggests interference with cAMP signalling. Submitted by: Eichinger Ludwig [ludwig.eichinger@uni-koeln.de] -------------------------------------------------------------------------------- A dual role for Rac1 GTPases in the regulation of cell motility Vedrana Filic, Maja Marinovic, Jan Faix and Igor Weber Journal of Cell Science, in press Rac proteins are the only canonical Rho family GTPases in Dictyostelium, where they act as key regulators of the actin cytoskeleton. In order to monitor the dynamics of activated Rac1 in Dictyostelium cells, a fluorescent probe was developed that specifically binds to GTP-bound form of Rac1. The probe is based on the GTPase-binding domain (GBD) from PAK1 kinase, and was selected on the basis of yeast two-hybrid, GST pull-down and fluorescence resonance energy transfer assays. PAK1_GBD localizes to leading edges of migrating cells and to endocytotic cups. As in vertebrates, activated Rac1 therefore appears to control de novo actin polymerization at protruding regions of the cell. Additionally, we found that the IQGAP- related protein DGAP1, which sequesters active Rac1 into a quaternary complex with actin-binding proteins cortexillin I and II, localizes to the trailing regions of migrating cells. Notably, PAK1_GBD and DGAP1, which both bind to Rac1-GTP, display mutually exclusive localizations in cell migration, phagocytosis and cytokinesis, and opposite dynamics of recruitment to the cell cortex upon stimulation with chemoattractants. Moreover, cortical localization of PAK1_GBD depends on integrity of the actin cytoskeleton, whereas cortical localization of DGAP1 does not. Taken together, these results imply that Rac1 GTPases play a dual role in regulation of cell motility and polarity in Dictyostelium. Submitted by Igor Weber [iweber@irb.hr] ============================================================== [End dictyNews, volume 37, number 4]