dictyNews Electronic Edition Volume 32, number 8 March 20, 2009 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 ========= Cortical Factor Feedback Model for Cellular Locomotion and Cytofission Shin I. Nishimura, Masahiro Ueda and Sasai Masaki PLoS Computational Biology 5(3):e1000310 (doi:10.1371) Eukaryotic cells can move spontaneously without being guided by external cues. For such spontaneous movements, a variety of different modes have been observed, including the amoeboid-like locomotion with protrusion of multiple pseudopods, the keratocyte-like locomotion with a widely spread lamellipodium, cell division with two daughter cells crawling in opposite directions, and fragmentations of a cell to multiple pieces. Mutagenesis studies have revealed that cells exhibit these modes depending on which genes are deficient, suggesting that seemingly different modes are the manifestation of a common mechanism to regulate cell motion. In this paper, we propose a hypothesis that the positive feedback mechanism working through the inhomogeneous distribution of regulatory proteins underlies this variety of cell locomotion and cytofission. In this hypothesis, a set of regulatory proteins, which we call cortical factors, suppress actin polymerization. These suppressing factors are diluted at the extending front and accumulated at the retracting rear of cell, which establishes a cellular polarity and enhances the cell motility, leading to the further accumulation of cortical factors at the rear. Stochastic simulation of cell movement shows that the positive feedback mechanism of cortical factors stabilizes or destabilizes modes of movement and determines the cell migration pattern. The model predicts that the pattern is selected by changing the rate of formation of the actin-filament network or the threshold to initiate the network formation. Submitted by: Shin Nishimura [shin@hiroshima-u.ac.jp] -------------------------------------------------------------------------------- The Effects of Extracellular Calcium on Motility, Pseudopod and Uropod Formation, Chemotaxis and the Cortical Localization of Myosin II in Dictyostelium discoideum Daniel F. Lusche, Deborah Wessels and David R. Soll The W.M. Keck Dynamic Image Analysis Facility Department of Biology The University of Iowa Iowa City, IA 52242 Cell Motility and the Cytoskeleton, in press Extracellular Ca++, a ubiquitous cation in the soluble environment of cells both free living and within the human body, regulates most aspects of amoeboid cell motility, including shape, uropod formation, pseudopod formation, velocity and turning in Dictyostelium discoideum. Hence it affects the efficiency of both basic motile behavior and chemotaxis. Extracellular Ca++ is optimal at 10 mM. A gradient of the chemoattractant cAMP generated in the absence of added Ca++ only affects turning, butin combination with extracellular Ca++, enhances the effects of extracellular Ca++. Potassium, at 40 mM, can substitute for Ca++. Mg++, Mn++, Zn++ and Na+ cannot. Extracellular Ca++, or K+, also induce the cortical localization of myosin II in a polar fashion. The effects of Ca++, K+ or a cAMP gradient do not appear to be similarly mediated by an increase in the general pool of free cytosolic Ca++. These results suggest a model, in which each agent functioning through different signaling systems, converge toaffect the cortical localization of myosin II, which in turn effects the behavioral changes leading to efficient cell motility and chemotaxis. Submitted by: Deborah Wessels [deborah-wessels@uiowa.edu] -------------------------------------------------------------------------------- Acidic Ca2+ stores, excitability and cell patterning in Dictyostelium discoideum Julian D. Gross Dept of Biochemistry, University of Oxford, Oxford OX13QU, United Kingdom Eukaryotic Cell, in press In this minireview I argue that the properties of the anterior and posterior cells of aggregates (slugs) can be accounted for by the following assumptions: 1) Cytosolic Ca2+ is sequestered into a specific type of internal store by an ATP-dependent Ca2+/H+ exchanger acting in conjunction with a vacuolar H+-ATPase that transfers protons into the compartment interior. 2) Cyclic AMP relay by the adenylyl cyclase, ACA, is dependent inter alia on cytosolic Ca2+ transients resulting from release of this stored Ca2+ in response to binding of cyclic AMP to its cell surface receptors 3) The vacuolar H+-ATPase is active in the anterior cells of aggregates but inactive in the posterior cells. The former can therefore fill these stores and experience Ca2+ transients, whereas the latter cannot. 4) The Ca2+ transients are responsible for driving prestalk cell-specific (PST) gene expression and inhibiting prespore cell specific (PSP) gene expression. Hence anterior cells express PST genes but not PSP genes, and posterior cells do not express PST genes. 5) Posterior cells express PSP genes as a result of activation of cAMP-dependent protein kinase A by cAMP generated by a separate, constitutively active, adenylyl cyclase (ACG), present only in the posterior cells. Submitted by: Julian Gross [julian@jdgross.fsworld.co.uk] ============================================================== [End dictyNews, volume 32, number 8]

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