dictyNews Electronic Edition Volume 36, number 9 March 18, 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 ========= Role of B regulatory subunits of PP2A in myosin II assembly control in Dictyostelium discoideum. Vandana Rai and Thomas Egelhoff Eukaryotic Cell, In Press In Dictyostelium discoideum, myosin II resides predominantly in a soluble pool, as the result of phosphorylation of the myosin heavy chain (MHC) and dephosphorylation of the MHC is required for myosin II filament assembly, recruitment to the cytoskeleton, and force production. Protein phosphatase type 2A (PP2A) was identified in earlier studies in Dictyostelium as a key biochemical activity that can drive MHC dephosphorylation. We report here gene targeting and cell biological studies addressing the roles of candidate PP2A B regulatory subunits (phr2aBalpha and phr2aBbeta) in myosin II assembly control in vivo. Dictyostelium phr2aBalpha and phr2aBbeta null cells show delayed development, reduction in the assembly of myosin II in cytoskeletal ghost assays, and defects in cytokinesis when grown in suspension, as compared to parental cell lines. These results demonstrate that the PP2A B subunits phr2aBalpha and phr2aBbeta contribute to myosin II assembly control in vivo, with phr2aBalpha having the predominant role facilitating MHC dephosphorylation to facilitate filament assembly. Submitted by Tom Egelhoff [tte@case.edu] --------------------------------------------------------------------------------- Chemotaxis: a feedback-based computational model robustly predicts multiple aspects of real cell behaviour. Matthew P. Neilson, Douwe Veltman, Peter van Haastert, Steven Webb, John Mackenzie and Robert H. Insall PLOS biology, in press Background: The mechanism of eukaryotic chemotaxis remains unclear despite intensive study. The most frequently described mechanism acts through attractants causing actin polymerization, in turn leading to pseudopod formation and cell movement. We recently proposed an alternative mechanism, supported by several lines of data, in which pseudopods are made by a self-generated cycle. If chemoattractants are present they modulate the cycle, rather than directly causing actin polymerization. The aim of this work is to test the explanatory and predictive powers of such pseudopod-based models to predict the complex behaviour of cells in chemotaxis. Results: We have now tested the effectiveness of this mechanism using a computational model of cell movement and chemotaxis based on pseudopod autocatalysis. The model reproduces a surprisingly wide range of existing data about cell movement and chemotaxis. It simulates cell polarization and persistence without stimuli, and selection of accurate pseudopods when chemoattractant gradients are present. It predicts both bias of pseudopod position in low chemoattractant gradients, and - unexpectedly - lateral pseudopod initiation in high gradients. To test the predictive ability of the model we looked for untested and novel predictions. One prediction from the model is that the angle between successive pseudopods at the front of the cell will increase in proportion to the difference between the cell's direction and the direction of the gradient. We measured the angles between pseudopods in chemotaxing Dictyostelium cells under different conditions, and found the results agreed with the model extremely well. Conclusions & Significance: Our model and data together suggest that in rapidly-moving cells like Dictyostelium and neutrophils an intrinsic pseudopod cycle lies at the heart of cell motility. This implies that the mechanism behind chemotaxis relies on modification of intrinsic pseudopod behaviour, more than generation of new pseudopods or actin polymerization by chemoattractants. Submitted by Robert Insall [R.Insall@beatson.gla.ac.uk] ============================================================== [End dictyNews, volume 36, number 9]