dictyNews Electronic Edition Volume 35, number 8 October 1, 2010 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 ========= Ras Proteins Have Multiple Functions In Vegetative Cells Of Dictyostelium Parvin Bolourani, George Spiegelman and Gerald Weeks Department of Microbiology and Immunology, Life Sciences Centre, University of British Columbia, Vancouver, B.C., Canada Eukaryotic Cell, in press During the aggregation of Dictyostelium cells, signaling through RasG is important in regulating cAMP chemotaxis, while signaling through RasC is important in regulating the cAMP relay. However, RasC is capable of substituting for RasG for chemotaxis, since rasG- null cells are only partially deficient in chemotaxis, while rasC-/rasG- cells are totally incapable of chemotaxis. In this study we have examined the possible functional overlap between RasG and RasC in vegetative cells by comparing the vegetative cell properties of rasG-, rasC- and rasC-/rasG- cells. In addition, since RasD, a protein not normally found in vegetative cells, is expressed in vegetative rasG- and rasC-/rasG- cells and appears to partially compensate for the absence of RasG, we have also examined the possible functional overlap between RasG and RasD, by comparing the properties of rasG- and rasC-/rasG- cells with those of the mutant cells expressing higher levels of RasD. The results of these two lines of investigation show that RasD is capable of totally substituting for RasG for cytokinesis and growth in suspension, while RasC is without effect. In contrast, for chemotaxis to folate, RasC is capable of partially substituting for RasG, but RasD is totally without effect. Finally neither RasC nor RasD is able to substitute for the role that RasG plays in regulating actin distribution and random motility. These specificity studies therefore delineate three distinct and none overlapping functions for RasG in vegetative cells. Submitted by Geryy Weeks [gerwee@interchange.ubc.ca] -------------------------------------------------------------------------------- Regulation of the actin cytoskeleton by an interaction of IQGAP related protein GAPA with Filamin and Cortexillin I Subhanjan Mondal, Bhagyashri Burgute, Daniela Rieger, Rolf Müller, Francisco Rivero, Jan Faix, Michael Schleicher, Angelika A. Noegel PLoS ONE, accepted Filamin and Cortexillin are F-actin crosslinking proteins in Dictyostelium discoideum allowing actin filaments to form three-dimensional networks. GAPA, an IQGAP related protein, is required for cytokinesis and localizes to the cleavage furrow during cytokinesis. Here we describe a novel interaction with Filamin which is required for cytokinesis and regulation of the F-actin content. The interaction occurs through the actin binding domain of Filamin and the GRD domain of GAPA. A similar interaction takes place with Cortexillin I. We further report that Filamin associates with Rac1a implying that filamin might act as a scaffold for small GTPases. Filamin and activated Rac associate with GAPA to regulate actin remodelling. Overexpression of filamin and GAPA in the various strains suggests that GAPA regulates the actin cytoskeleton through interaction with Filamin and that it controls cytokinesis through association with Filamin and Cortexillin. Submitted by Angelika Noegel [noegel@uni-koeln.de] -------------------------------------------------------------------------------- Phospholipase D Controls Dictyostelium Development By Regulating G Protein Signaling Sibnath Ray, Yi Chen, Joanna Ayoung, Rachel Hanna and Derrick Brazill* Journal of Cellular Signalling, in press Dictyostelium discoideum cells normally exist as individual amoebae, but will enter a period of multicellular development upon starvation. The initial stages of development involve the aggregation of individual cells, using cAMP as a chemoattractant. Chemotaxis is initiated when cAMP binds to its receptor, cAR1, and activates the associated G protein, Galpha2betagamma. However, chemotaxis will not occur unless there is a high density of starving cells present, as measured by high levels of the secreted quorum sensing molecule, CMF. We previously demonstrated that cells lacking PldB bypass the need for CMF and can aggregate at low cell density, whereas cells overexpressing pldB do not aggregate even at high cell density. Here, we found that PldB controlled both cAMP chemotaxis and cell sorting. PldB was also required by CMF to regulate G protein signaling. Specifically, CMF used PldB, to regulate the dissociation of Galpha2 from Gbetagamma. Using fluorescence resonance energy transfer (FRET), we found that along with cAMP, CMF increased the dissociation of the G protein. In fact, CMF augmented the dissociation induced by cAMP. This augmentation was lost in cells lacking PldB. PldB appears to mediate the CMF signal through the production of phosphatidic acid, as exogenously added phosphatidic acid phenocopies overexpression of pldB. These results suggest that phospholipase D activity is required for CMF to alter the kinetics of cAMP-induced G protein signaling. Submitted by Derrick Brazill [brazill@genectr.hunter.cuny.edu] ============================================================== [End dictyNews, volume 35, number 8]