dictyNews Electronic Edition Volume 36, number 11 April 01, 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 ========= Cell condition, competition, and chimerism in the social amoeba Dictyostelium discoideum David I. Castillo1, David C. Queller1, Joan E. Strassmann1 1Department of Ecology and Evolutionary Biology, Rice University, Houston, TX, 77005 USA Ecology, Ethology, and Evolution, in press When multicellularity originates through the aggregation of genetically variable cells, the interests of the component cells may conflict with each other. A prediction of conflict is that stronger cells will force weaker cells into non-reproductive tissues. However, if stronger cells are better in the reproductive tissues than in the somatic ones, then the same result may be expected in clonal organisms that optimize their development. We explored these issues in the social amoeba Dictyostelium discoideum by forming chimeras between weakened cells and normal cells that were genetically identical. We reduced the condition of amoebae (measured as increased doubling time) by growing them in media lacking glucose, or more acid than normal. Weakened cells were less competitive compared to healthy cells in becoming spore, supporting our prediction of evolutionary conflict. However, spores from weakened cells also proliferated slightly less rapidly than normal spores, indicating that there may also be an advantage in clonal groups to put strong cells in spores. Submitted by Joan E. Strassmann [strassm@rice.edu] ------------------------------------------------------------------ Activated membrane patches guide chemotactic cell motility Inbal Hecht*1,2, Monica L. Skoge3, Pascale G. Charest3, Eshel Ben-Jacob2, Richard A. Firtel3, William F. Loomis3, Herbert Levine1,4, Wouter-Jan Rappel*1,4 1) Center for Theoretical Biological Physics, University of California San Diego, La Jolla, CA 92093, 2) School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, 3) Cell and Developmental Biology, Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093, 4) Department of Physics, University of California San Diego, La Jolla, CA 92093 PLoS Computational Biology, in press Many eukaryotic cells are able to crawl on surfaces and guide their motility based on environmental cues. These cues are interpreted by signaling systems which couple to cell mechanics; indeed membrane protrusions in crawling cells are often accompanied by activated membrane patches, which are localized areas of increased concentration of one or more signaling components. To determine how these patches are related to cell motion, we examine the spatial localization of RasGTP in chemotaxing Dictyostelium discoideum cells under conditions where the vertical extent of the cell was restricted. Quantitative analyses of the data reveal a high degree of spatial correlation between patches of activated Ras and membrane protrusions. Based on these findings, we formulate a model for amoeboid cell motion that consists of two coupled modules. The first module utilizes a recently developed two-component reaction diffusion model that generates transient and localized areas of elevated concentration of one of the components along the membrane. The activated patches determine the location of membrane protrusions (and overall cell motion) that are computed in the second module, which also takes into account the cortical tension and the availability of protrusion resources. We show that our model is able to produce realistic amoeboid-like motion and that our numerical results are consistent with experimentally observed pseudopod dynamics. Specifically, we show that the commonly observed splitting of pseudopods can result directly from the dynamics of the signaling patches. Submitted by Bill Loomis [wloomis@ucsd.edu] ============================================================== [End dictyNews, volume 36, number 11]