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]