dictyNews Electronic Edition Volume 43, number 25 October 20, 2017 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 ========= GPCR-controlled Membrane Recruitment of Negative Regulator C2GAP1 Locally Inhibits Ras Signaling for Adaptation and Long-range Chemotaxis Xuehua Xua, Xi Wen, Douwe M. Veltman, Ineke Keizer-Gunnink, Henderikus Pots, Arjan Kortholt, and Tian Jin PNAS, USA, accepted Eukaryotic cells chemotax in a wide range of chemoattractant concentration gradients, and thus need inhibitory processes that terminate cell responses to reach adaptation while maintaining sensitivity to higher-concentration stimuli. However, the molecular mechanisms underlying inhibitory processes are still poorly understood. Here, we reveal a locally controlled inhibitory process in a GPCR-mediated signaling network for chemotaxis in Dictyostelium discoideum. We identified a novel negative regulator of Ras signaling, C2GAP1, which localizes at the leading edge of chemotaxing cells and is activated by and essential for GPCR-mediated Ras signaling. We show that both C2 and GAP domains are required for the membrane targeting of C2GAP1, and that GPCR-triggered Ras activation is necessary to recruit C2GAP1 from the cytosol and retains it on the membrane to locally inhibit Ras signaling. C2GAP1-deficient c2gapA- cells have altered Ras activation that results in impaired gradient sensing, excessive polymerization of F-actin, and subsequent defective chemotaxis. Remarkably, these cellular defects of c2gapA- cells are chemoattractant concentration-dependent. Thus, we have uncovered a novel inhibitory mechanism required for adaptation and long-range chemotaxis. submitted by: Xuehua Xu [xxu@niaid.nih.gov] —————————————————————————————————————— The fate of multilamellar bodies produced and secreted by Dictyostelium discoideum amoebae Alix M. Denoncourt1,2,3, Alicia F. Durocher1,2,3, Valérie E. Paquet1,2,3 and Steve J. Charette1,2,3* 1. Institut de Biologie Intégrative et des Systèmes, Pavillon Charles- Eugène-Marchand, Université Laval, Quebec City, QC, Canada 2. Centre de recherche de l’Institut universitaire de cardiologie et de pneumologie de Québec, Hôpital Laval, Quebec City, QC, Canada 3. Département de biochimie, de microbiologie et de bio-informatique, Faculté des sciences et de génie, Université Laval, Quebec City, QC, Canada European Journal of Cell Biology, accepted The amoeba Dictyostelium discoideum produces and secretes multilamellar bodies (MLBs) mainly composed of amoebal membranes upon digestion of bacteria. After their secretion, the fate of these MLBs remains unknown. The aim of this study was to determine if protozoa can internalize and digest secreted D. discoideum MLBs. Our results showed that MLBs were ingested by naive axenic D. discoideum cells (i. e. cells not exposed to bacteria and consequently not producing MLBs). Only a small fraction of the ingested MLBs were found in cells’ post-lysosomes compared to undigestible beads suggesting that naive amoebae digest them. D. discoideum MLBs were also ingested by the ciliates Tetrahymena pyriformis and Tetrahymena thermophila. MLBs internalized by the ciliates were compacted into pellets and expelled in the extracellular medium without obvious signs of degradation. The results of this study provide new insights on the biological function of MLBs and, considering that MLBs are also involved in bacteria packaging, suggest additional layers of complexity in microbial interactions. submitted by: Steve Charette [steve.charette@bcm.ulaval.ca] —————————————————————————————————————— G-Protein Dependent Signal Transduction and Ubiquitination in Dictyostelium Barbara Pergolizzi , Salvatore Bozzarro and Enrico Bracco Int. J. Mol. Sci. 2017, accepted Signal transduction through G-protein-coupled receptors (GPCRs) is central for the regulation of virtually all cellular functions, and it has been widely implicated in human diseases.These receptors activate a common molecular switch that is represented by the heterotrimeric G-protein generating a number of second messengers (cAMP, cGMP, DAG, IP3, Ca2+ etc.), leading to a plethora of diverse cellular responses. Spatiotemporal regulation of signals generated by a given GPCR is crucial for proper signalling and is accomplished by a series of biochemical modifications. Over the past few years, it has become evident that many signalling proteins also undergo ubiquitination, a posttranslational modification that typically leads to protein degradation, but also mediates processes such as protein-protein interaction and protein subcellular localization. The social amoeba Dictyostelium discoideum has proven to be an excellent model to investigate signal transduction triggered by GPCR activation, as cAMP signalling via GPCR is a major regulator of chemotaxis, cell differentiation, and multicellular morphogenesis. Ubiquitin ligases have been recently involved in these processes. In the present review, we will summarize the most significant pathways activated upon GPCRs stimulation and discuss the role played by ubiquitination in Dictyostelium cells. submitted by: Barbara Pergolizzi [barbara.pergolizzi@unito.it] ============================================================== [End dictyNews, volume 43, number 25]