Dicty News Electronic Edition Volume 19, number 1 July 20, 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. ====================== Position Available ====================== Postdoctoral fellow position available in our Cell Dynamics group Applications are invited for a postdoctoral position funded by a Wellcome Trust grant for 3 years, to study the mechanisms of phagocytosis by applying proteomic and lipidomic analysis tools. We have recently established and improved a phagosome purification protocol that allows access to large quantities of lipids and proteins at any time point of phagosome maturation. The preliminary molecular characterisation is in press in MBC and we want to further the investigation of wild type and mutant strains with phagocytic impairments. As the components of the complex machineries involved are evolutionarily conserved, their molecular and cellular dissection in Dictyostelium is directly relevant to unravel their functional importance in higher organisms. A description of this and other projects of the group is available at: http://www.bio.ic.ac.uk/research/tps/ The candidate should be motivated and enthusiastic about this area of research. Proficiency in a variety of techniques, including cell culture, single cell assays, biophysical and biochemical methods, microscopy and bioinformatics will be a determining asset for the successful candidate. For further details, please contact Dr. Thierry Soldati, Department of Biological Sciences, Imperial College of Science, Technology and Medicine, Exhibition Road, London, SW7 2AZ. E-mail t.soldati@ic.ac.uk. To apply, please, send a full CV, a description of current research and interests, and the name of two referees at the same address. ============= Abstracts ============= High resolution dissection of phagosome maturation reveals distinct membrane trafficking phases Daniel Gotthardt, Hans Jrg Warnatz, Oliver Henschel, Franz Brckert, Michael Schleicher, and Thierry Soldati Molecular Biology of the Cell, in press Abstract Molecular mechanisms of endocytosis in the genetically and biochemically tractable professional phagocyte Dictyostelium discoideum reveal a striking degree of similarity to higher eukaryotic cells. Pulse-chase feeding with latex beads allowed purification of phagosomes at different maturation stages. Gentle ATP-stripping of an actin meshwork entrapping contaminating organelles resulted in a 10-fold increase in yield and purity, as confirmed by EM. Temporal profiling of signaling, cytoskeletal and trafficking proteins resulted in a complex molecular fingerprint of phagosome biogenesis and maturation. First, nascent phagosomes were associated with coronin, and rapidly received a lysosomal glycoprotein, LmpB. Second, at least two phases of delivery of lysosomal hydrolases (CatD and CP34) were accompanied by removal of plasma membrane components (PM4C4 and biotinylated surface proteins). Third, a phase of late maturation, preparing for final exocytosis of undigested material, included quantitative recycling of hydrolases and association with vacuolin. Also, lysosomal glycoproteins of the Lmp family showed distinct trafficking kinetics. The delivery and recycling of CatD was directly visualized by confocal microscopy. This heavy membrane traffic of cargos was precisely accompanied by regulatory proteins such as the Rab7 GTPases and the endosomal SNAREs Vti1 and VAMP7. This initial molecular description of phagocytosis demonstrates the feasibility of a comprehensive analysis of phagosomal lipids and proteins in genetically modified strains. ---------------------------------------------------------------------------- Possible Role of Contact Following in the Generation of Coherent Motion of Dictyostelium Cells Tamiki Umeda* and Kei Inouye** *Department of Marine Engineering, Kobe University of Mercantile Marine, Kobe 658-0022, Japan, **Department of Botany, Division of Biological Science, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan J. theor. Biol. in press After aggregation by chemotaxis, cells of the cellular slime mold Dictyostelium discoideum form a multicellular structure and show coherent motion such as vortices. Here we present a mathematical model to explain both aggregation and coherent motion of cells in two-dimensional space. The model incorporates chemotactic response of cells and the cell's property, called "contact following", to follow the other cells with which they are in contact. Analytical study and computer simulation using the model show that with contact following cells form circular clusters within which cell rotation occurs. Unidirectional cell motion in a long belt of cells is another type of solution of the model. Besides, contact following has an effect to accelerate cell cluster merging. By considering the mechanism of cell movement, possible explanations of contact following are proposed. ----------------------------------------------------------------------------- Unique Behavior of a Dictyostelium Homologue of TRAP-1, Coupling with Differentiation of D. discoideum cells Tsuyoshi Morita, Aiko Amagai and Yasuo Maeda Experimental Cell Research, in press Dd-TRAP1 is a Dictyostelium homologue of TRAP-1, a human protein that binds to the type1 tumor necrosis factor (TNF) receptor. TRAP-1 has a putative mitochondrial localization sequence and shows significant homology to members of HSP90 family. Although the TRAP-1 is mainly localized to mitochondria in several mammalian cells, in certain tissues it is also localized at specific extramitochondrial sites. In Dictyostelium cells, Dd-TRAP1 is predominantly located in the cell membrane/cortex during growth and just after starvation. Double staining of vegetatively growing cells with the anti-Dd-TRAP1 antibody and TRITC-phalloidin has demonstrated co-localization of Dd-TRAP1 and F-actin at the leading edge of cortical protrusions such as pseudopodes. Coupled with differentiation, however, Dd-TRAP1 located at the cortical region is translocated to mitochondria in spite of the absence of the mitochondrial localization sequence at its N-terminus. The translocation of this protein raises interesting and fundamental questions regarding possible mechanisms by which the Dd-TRAP1 is involved in cellular differentiation. ----------------------------------------------------------------------------- [End Dicty News, volume 19, number 1]