Dicty News Electronic Edition Volume 15, number 3 July 27, 2000 ***Special Pre Meeting Edition*** Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@nwu.edu. Back issues of Dicty-News, the Dicty Reference database and other useful information is available at the Dictyostelium Web Page "http://dicty.cmb.nwu.edu/dicty" ============== Abstracts ============== Spontaneous symmetry breaking Turing-type pattern formation in a confined Dictyostelium cell mass Satoshi Sawai1, Yasuo Maeda2 and Yasuji Sawada3 1Graduate School of Information Sciences, Tohoku University, Katahira, Sendai 980-8577, 2Biological Institute, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, and 3Research Institute of Electrical Communication, Tohoku University, Katahira, Sendai 980-8577, Japan. Phys. Rev. Lett., in press Summary We have discovered a new type patterning which occurs in a two dimensionally confined cell mass of the cellular slime mold Dictyostelium discoideum. Adding to the longitudinal structure reported earlier, we observed a spontaneous symmetry breaking spot pattern whose wavelength show a similar strain dependency to that of the longitudinal one. We propose these structures are due to a reaction-diffusion Turing instability which has been exemplified by CIMA(chloride-iodide-maloic acid) reaction. The present finding may exhibit a first biochemical Turing structure in a developmental system with a controllable boundary condition. ---------------------------------------------------------------------------- Dynacortin, a genetic link between equatorial contractility and global shape control discovered by library complementation of a Dictyostelium cytokinesis mutant. Douglas N. Robinson and James A. Spudich. Department of Biochemistry, Beckman Center, Rm. B-400, Stanford University, Stanford, CA 94305-5307, USA J. Cell Biol. In press Abstract We have developed a system for performing interaction genetics in Dictyostelium discoideum that uses a cDNA library complementation/multicopy suppression strategy. Chemically-mutagenized cells were screened for cytokinesis-deficient mutants and one mutant was subjected to library complementation. Isolates of four different genes were recovered as modifiers of this strain’s cytokinesis defect. These include the cleavage furrow protein cortexillin I, a novel protein we named dynacortin, an ezrin-radixin-moesin-family protein, and coronin. The cortexillin I locus and transcript were found to be disrupted in the strain, identifying it as the affected gene. Dynacortin is localized partly to the cell cortex and becomes enriched in protrusive regions, a localization pattern that is similar to coronin and partly dependent on RacE. During cytokinesis, dynacortin is found in the cortex and is somewhat enriched at the poles. Furthermore, it appears to be reduced in the cleavage furrow. The genetic interactions and the cellular distributions of the proteins suggest a hypothesis for cytokinesis in which the contraction of the medial ring is a function of spatially-restricted cortexillin I and myosin II and globally-distributed dynacortin, coronin, and RacE. ---------------------------------------------------------------------------- Ca2+ signalling is not required for chemotaxis in Dictyostelium David Traynor, Jacqueline L.S. Milne**, Robert H. Insall* and Robert R. Kay MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH,England *School of Biosciences, University of Birmingham, Birmingham, B15 2TT,England **current address: Laboratory of Cell Biology, National Cancer Institute, Bethesda, Maryland 20892, USA EMBO Journal, in press. ABSTRACT Dictyostelium cells can rapidly move towards a source of cyclic-AMP. This chemoattractant is detected by G-protein-linked receptors, which trigger a signalling cascade including a rapid influx of Ca2+. We have disrupted an InsP3 (inositol 1,4,5-trisphosphate) receptor-like gene, iplA, to produce null cells in which Ca2+ entry in response to chemoattractants is abolished, as is the normal increase in cytosolic Ca2+ that follows chemotactic stimulation. However, the resting cytosolic Ca2+ concentration is similar to wild-type. This mutant provides a test for the role of Ca2+ influx in both chemotaxis and the signalling cascade that controls it. The production of cyclic-GMP, cyclic-AMP and the activation of the MAP kinase, DdERK2, triggered from the cyclic-AMP receptor, are little perturbed in the mutant; mobilization of actin into the cytoskeleton also follows similar kinetics to wild-type. Mutant cells chemotax efficiently towards cyclic-AMP or folic acid and their sensitivity to cyclic-AMP is similar to wild-type. Finally, they move at similar speeds to wild-type cells, with or without chemoattractant. We conclude that Ca2+ signalling is not necessary for chemotaxis to cyclic-AMP. ---------------------------------------------------------------------------- Identification and Characterization of Two Flavohemoglobin Genes in Dictyostelium discoideum Miho Iijima, Hajime Shimizua, Yoshimasa Tanaka and Hideko Urushihara* Cell Structure and Function, in press. Flavohemoglobins are being identified in an expanding number of prokaryotes and unicellular eukaryotes. These molecules consist of an N-terminal hemoglobin domain and a C-terminal oxidoreductase domain, and are considered to function in storage or as sensors for O2, and in defense against oxidative stress and/or NO. However, their physiological significance has not yet been determined. Here, we isolated and analyzed two flavohemoglobin genes of Dictyostelium discoideum, DdFHa and DdFHb, which lie close to each other in the genome. DdFHs were induced by submerged conditions, and enriched in the sexually mature cells of D. discoideum. Although they were not essential for growth or development under standard laboratory conditions, disruption of both genes caused an increase in number of large but uninuclear cells, and hypersensitivity to higher concentrations of glucose and to NO releasers. These results indicate that DdFHs are responsible for transducing NO signals to maintain normal cellular conditions against environmental stresses. ---------------------------------------------------------------------------- [End Dicty News, volume 15, number 3]