dictyNews Electronic Edition Volume 37, number 16 December 16, 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 ========= The IplA Ca++ Channel Of Dictyostelium discoideum Is Necessary For Ca++, Not cAMP, Chemotaxis, And Plays A Fundamental Role In Natural Aggregation Daniel F. Lusche, Deborah Wessels, Amanda Scherer, Karla Daniels, Spencer Kuhl and David R. Soll W.M. Keck Dynamic Image Analysis Facility Department of Biology, University of Iowa, Iowa City, IA 52242 J. Cell Science, in press During aggregation of Dictyostelium discoideum, nondissipating, symmetric, outwardly moving waves of cAMP direct cells towards aggregation centers. It has been assumed that the spatial and temporal characteristics of the front and back of each cAMP wave regulate both chemokinesis and chemotaxis. However, during the period preceding aggregation, cells acquire not only the capacity to chemotax in a spatial gradient of cAMP, but also in a spatial gradient of Ca++. The null mutant of the putative iplA Ca++ channel gene, iplA-, undergoes normal chemotaxis in spatial gradients of cAMP and normal chemokinetic responses to increasing temporal gradients of cAMP, both generated in vitro. However, iplA- cells lose the capacity to undergo chemotaxis in response to a spatial gradient of Ca++, suggesting that IplA is either the Ca++ chemotaxis receptor or an essential component of the Ca++ chemotaxis regulatory pathway. In response to natural chemotactic waves generated by wild type cells, the chemokinetic response of iplA- cells to the temporal dynamics of the cAMP wave is intact, but the capacity to reorient in the direction of the aggregation center at the onset of each wave is lost. These results suggest a model in which transient Ca++ gradients formed between cells at the onset of each natural cAMP wave augment reorientation towards the aggregation center. If this hypothesis proves correct, it will provide a more complex contextual framework for interpreting D. discoideum chemotaxis. Submitted by Deborah Wessels [deborah-wessels@uiowa.edu] -------------------------------------------------------------------------------------- Incoherent Feedforward Control Governs Adaptation of Activated Ras in a Eukaryotic Chemotaxis Pathway Kosuke Takeda, Danying Shao, Micha Adler, Pascale G. Charest, William F. Loomis, Herbert Levine, Alex Groisman, Wouter-Jan Rappel and Richard A. Firtel. Section of Cell and Developmental Biology, Division of Biological Sciences, and Department of Physics Science Signaling, in press Adaptation in signaling systems, during which the output returns to a fixed base-amount following a change in the input, often involves negative feedback loops and plays a crucial role in eukaryotic chemotaxis. We determined the dynamical response of a eukaryotic chemotaxis pathway immediately downstream from G protein-coupled receptors following a uniform change in chemoattractant concentration. We found that the response of an activated Ras shows near perfect adaptation. We attempted to fit the results using mathematical models for the two possible simple network topologies that can provide perfect adaptation. Only the incoherent feedforward network was able to accurately describe the experimental results. This analysis revealed that adaptation in this Ras pathway is achieved through the proportional activation of upstream components and not through negative feedback loops. Furthermore, these results are consistent with a local excitation, global inhibition mechanism for gradient sensing, possibly with a RasGAP as a global inhibitor. Submitted by Bill Loomis [wloomis@ucsd.edu] -------------------------------------------------------------------------------------- High relatedness is necessary and sufficient to maintain multicellularity in Dictyostelium Jennie J. Kuzdzal-Fick 1,2, Sara A. Fox 1, Joan E. Strassmann 1,3, David C. Queller 1,3 1 Department of Ecology and Evolutionary Biology, Rice University, 6100 Main Street, Houston, TX 77005 2 Section of Integrative Biology, College of Natural Sciences, The University of Texas at Austin, University Station C0930, Austin, TX 78712 3 Department of Biology CB1137, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130 Science 16 December 2011, Vol. 334 no. 6062 pp. 1548-1551, DOI: 10.1126/science.1213272 One sentence summary: Experimental evolution studies show that the extraordinary cooperation of cells in multicellular organisms degrades under low relatedness, but is preserved under the high relatedness generated by single-cell bottlenecks in the life cycle. Abstract. Most complex multicellular organisms develop clonally from a single cell. This should limit conflicts between cell lineages that could threaten the extensive cooperation of cells within multicellular bodies. Cellular composition can be manipulated in the social amoeba Dictyostelium discoideum, allowing us to test and confirm the two key predictions of this theory. Experimental evolution at low relatedness favored cheating mutants that could destroy multicellular development. However, under high relatedness the forces of mutation and within- individual selection are too small for these destructive cheaters to spread as shown by a mutation accumulation experiment. Thus we conclude that the single-cell bottleneck is a powerful stabilizer of cellular cooperation in multicellular organisms. Submitted by Jennie Kuzdzal-Fick [kuzdzalfick@mail.utexas.edu] ============================================================== [End dictyNews, volume 37, number 16]