dictyNews Electronic Edition Volume 40, number 31 December 12, 2014 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 Dictyostelium prestalk inducer Differentiation Inducing Factor-1 (DIF-1) triggers unexpectedly complex global phosphorylation changes Chris Sugden*, Michael D. Urbaniak@, Tsuyoshi Araki* and Jeffrey G. Williams* *The College of Life Sciences, University of Dundee, Dow St., Dundee DD1 5EH, UK. @Division of Biomedical and Life Sciences, Faculty of Health and Medicine, Lancaster University, Bailrigg, Lancaster LA1 4YG, UK. Address correspondence to: Jeffrey G. Williams (J.G.Williams@dundee.ac.uk) Abbreviations: DIF-1, Differentiation Inducing Factor-1; SILAC, Stable Isotope Labeling by Amino Acids in Cell Culture Mol Biol of the Cell (MBoC), in press DIF-1 is a polyketide that induces Dictyoselium amoebae to differentiate as prestalk cells. We performed a global quantitative screen for phosphorylation changes that occur within the first minutes after addition of DIF-1 using a triple-label SILAC approach. This revealed a new world of DIF-1 controlled signalling: with changes in components of the MAPK and protein kinase-B signalling pathways, components of the actinomyosin cytoskeletal signalling networks and in a broad range of small GTPases and their regulators. The results also provide evidence that the Ca2+/calmodulin dependent phosphatase calcineurin plays a role in DIF-1 signalling to the DimB prestalk transcription factor. At the global level DIF-1 causes a major shift in the phosphorylation/dephosphorylation equilibrium towards net dephosphorylation. Interestingly, many of the sites that are dephosphorylated in response to DIF-1 are phosphorylated in response to extracellular cAMP signalling. This accords with studies that suggest an antagonism between the two inducers and also with the rapid dephosphorylation of the cAMP receptor that we observe in response to DIF-1 and with the known inhibitory effect of DIF-1 on chemotaxis to cAMP. Submitted by Jeff Williams [j.g.williams@dundee.ac.uk] ---------------------------------------------------------------------- Image based validation of dynamical models for cell reorientation Robert Lockley (1), Graham Ladds (2) and Till Bretschneider (1) 1 Warwick Systems Biology Centre, Senate House, University of Warwick, Coventry, United Kingdom 2 Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry, United Kingdom Cytometry A, first published online (open access): 9 DEC 2014 DOI: 10.1002/cyto.a.22600 A key feature of directed cell movement is the ability of cells to reorient quickly in response to changes in the direction of an extracellular stimulus. Mathematical models have suggested quite different regulatory mechanisms to explain reorientation, raising the question of how we can validate these models in a rigorous way. In this study, we fit three reactionÐdiffusion models to experimental data of Dictyostelium amoebae reorienting in response to alternating gradients of mechanical shear flow. The experimental readouts we use to fit are spatio-temporal distributions of a fluorescent reporter for cortical F-actin labeling the cell front. Experiments performed under different conditions are fitted simultaneously to challenge the models with different types of cellular dynamics. Although the model proposed by Otsuji is unable to provide a satisfactory fit, those suggested by Meinhardt and Levchenko fit equally well. Further, we show that reduction of the three-variable Meinhardt model to a two-variable model also provides an excellent fit, but has the advantage of all parameters being uniquely identifiable. Our work demonstrates that model selection and identifiability analysis, commonly applied to temporal dynamics problems in systems biology, can be a powerful tool when extended to spatio-temporal imaging data. Submitted by Till Bretschneider [T.Bretschneider@warwick.ac.uk] ---------------------------------------------------------------------- c-di-GMP induction of Dictyostelium cell death requires the polyketide DIF-1 Yu Song, Marie-Francoise Luciani, Corinne Giusti, and Pierre Golstein Centre dÕImmunologie de Marseille-Luminy, UM2 Aix-Marseille Universite, Case 906, 13288 Marseille cedex 9, France; INSERM, U1104, 13288 Marseille, France; CNRS, UMR7280, 13288 Marseille, France. Address correspondence to: Pierre Golstein (golstein@ciml.univ-mrs.fr) Mol Biol of the Cell (MBoC), in press Cell death in the model organism Dictyostelium, as studied in monolayers in vitro, can be induced by the polyketide DIF-1 or by the cyclic dinucleotide c-di-GMP. c-di-GMP, a universal bacterial second messenger, can trigger innate immunity in bacterially-infected animal cells, and is involved in developmental cell death in Dictyostelium. We show here that c-di-GMP was not sufficient to induce cell death in Dictyostelium cell monolayers. Unexpectedly, it also required the DIF-1 polyketide. The latter could be exogenous, as revealed by a telling synergy between c-di-GMP and DIF-1. The required DIF-1 polyketide could also be endogenous, as shown by the inability of c-di-GMP to induce cell death in Dictyostelium HMX44A cells and DH1 cells upon pharmacological or genetic inhibition of DIF-1 biosynthesis. In these cases c-di-GMP-induced cell death was rescued by complementation with exogenous DIF-1. Altogether, these results demonstrated that c-di- GMP could trigger cell death in Dictyostelium only in the presence of the DIF-1 polyketide or its metabolites. This identified another element of control to this cell death and perhaps also to c-di-GMP effects in other situations and organisms. Submitted by Pierre Golstein [golstein@ciml.univ-mrs.fr] ============================================================== [End dictyNews, volume 40, number 31]