dictyNews Electronic Edition Volume 39, number 18 June 21, 2013 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 ========= Lipid composition of multilamellar bodies secreted by Dictyostelium discoideum reveals their amoebal origin. Paquet VE, Lessire R, Domergue F, Fouillen L, Filion G, Sedighi A, Charette SJ. Institut de Biologie Integrative et des Systemes, Universite Laval, Quebec City, Quebec, Canada, G1V 0A6. Eukaryot Cell. 2013 Jun 7. [Epub ahead of print] When they are fed with bacteria, Dictyostelium discoideum amoebae produce and secrete multilamellar bodies (MLBs), which are composed of membranous material. It has been proposed that MLBs are a waste disposal system allowing D. discoideum to eliminate undigested bacterial remains. However, the real function of MLBs remains unknown. Determining the biochemical composition of MLBs, especially lipids, represents a way to gain information about the role of these structures. To allow these analyses, a protocol involving various centrifugation procedures has been developed to purify secreted MLBs from amoebae-bacteria co-cultures. The purity of MLB preparation was confirmed by transmission electron microscopy and by immunofluorescence using H36, an antibody that binds to MLBs. The lipid and fatty acid compositions of pure MLBs were then analyzed by high performance thin layer chromatography (HPTLC) and gas chromatography (GC), respectively, and compared to those of amoebae as well as bacteria used as food source. While the bacteria were devoid of phosphatidylcholine (PC) and phosphatidylinositol (PI), these two polar lipid species were major classes of lipids in MLBs and amoebae. Similarly, the fatty acid composition of MLBs and amoebae was characterized by the presence of polyunsaturated fatty acids while cyclic fatty acids were found only in bacteria. These results strongly suggest that the lipids constituting the MLBs rather originate from the amoebal metabolism rather than from undigested bacterial membranes. This opens the possibility that MLBs, instead of being a waste disposal system, have unsuspected roles in D. discoideum physiology. Submitted by Steve Charette [steve.charette@bcm.ulaval.ca] --------------------------------------------------------------------------- Laurence Aubry & Gerard Klein True Arrestins and Arrestin-Fold Proteins: A Structure-Based Appraisal. Progress in Molecular Biology and Translational Science, Louis M. Luttrell, editor, Vol. 118, Burlington: Academic Press, 2013, pp. 21-56. ISBN: 978-0-12-394440-5 Arrestin-clan proteins are folded alike, a feature responsible for their recent grouping in a single clan. In human, it includes the well-characterized visual and beta-arrestins, the arrestin domain-containing proteins (ARRDCs), isoforms of the retromer subunit VPS26, and DSCR3, a protein involved in Down syndrome. A new arrestin-fold-predicted protein, RGP1, described here may join the clan. Unicellular organisms like the yeast Saccharomyces cerevisiae or the amoeba Dictyostelium discoideum harbor VPS26, DSCR3, and RGP1 isoforms as well as arrestin-related trafficking adaptors or ADCs, but true arrestins are missing. Functionally, members of the arrestin clan have generally a scaffolding role in various membrane protein trafficking events. Despite their similar structure, the mechanism of cargo recognition and internalization and the nature of recruited partners differ for the different members. Based on the recent literature, true arrestins (visual and beta-arrestins), ARRDCs, and yeast ARTS are the closest from a functional point of view. Submitted by Laurence Aubry [laubry@cea.fr] --------------------------------------------------------------------------- Analysis of phenotypic evolution in Dictyostelia highlights developmental plasticity as a likely consequence of colonial multicellularity Maria Romeralo1,2, Anna Skiba1, Alejandro Gonzalez-Voyer3, Christina Schilde1, Hajara Lawal1, Sylwia Kedziora1, Jim C. Cavender4, Gernot Gloeckner5,6, Hideko Urushihara7 and Pauline Schaap1 1College of Life Sciences, University of Dundee, Dundee, UK 2Department of Systematic Biology, Uppsala University, Uppsala, Sweden 3Department of Integrative Ecology, Estacion Biologica de Donana (EBD-CSIC), Sevilla, Spain 4Department of Environmental and Plant Biology, Ohio University, Athens, OH, USA 5Department of Genomics, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, IGB, Berlin, Germany 6Institute for Biochemistry I, University of Cologne, Cologne, Germany 7Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba-shi, Japan Proc. R. Soc. B., in press Colony formation was the first step towards evolution of multicellularity in many macroscopic organisms. Dictyostelid social amoebas have used this strategy for over 600 Myr to form fruiting structures of increasing complexity. To understand in which order multicellular complexity evolved, we measured 24 phenotypic characters over 99 dictyostelid species. Using phylogenetic comparative methods, we show that the last common ancestor (LCA) of Dictyostelia probably erected small fruiting structures directly from aggregates. It secreted cAMP to coordinate fruiting body morphogenesis, and another compound to mediate aggregation. This phenotype persisted up to the LCAs of three of the four major groups of Dictyostelia. The group 4 LCA co-opted cAMP for aggregation and evolved much larger fruiting structures. However, it lost encystation, the survival strategy of solitary amoebas that is retained by many species in groups 1-3. Large structures, phototropism and a migrating intermediate 'slug' stage coevolved as evolutionary novelties within most groups. Overall, dictyostelids show considerable plasticity in the size and shape of multicellular structures, both within and between species. This probably reflects constraints placed by colonial life on developmental control mechanisms, which, depending on local cell density, need to direct from 10 to a million cells into forming a functional fructification. Submitted by Pauline Schaap [p.schaap@dundee.ac.uk] --------------------------------------------------------------------------- Two distinct functions for PI3-kinases in macropinocytosis Oliver Hoeller, Parvin Bolourani, Jonathan Clark, Len R. Stephens, Phillip T. Hawkins, Orion D. Weiner, Gerald Weeks & Robert R. Kay Journal of Cell Science, in press Class-1 PI3-kinases are major regulators of the actin cytoskeleton, whose precise contributions to chemotaxis, phagocytosis and macropinocytosis remain unresolved. We use systematic genetic ablation to examine this question in growing Dictyostelium cells. Mass-spectroscopy shows that a quintuple mutant lacking the entire genomic complement of class-1 PI3-kinases retains only 10% of wild-type PIP3 levels. Chemotaxis to folate and phagocytosis of bacteria proceed normally in the quintuple mutant but macropinocytosis is abolished. In this context PI3-kinases show specialized functions, only one of which is directly linked to gross PIP3 levels: Macropinosomes originate in patches of PIP3, with associated F-actin rich ruffles, both of which depend on PI3K1/2 but not PI3K4, whereas conversion of ruffles into vesicles requires PI3K4. A biosensor derived from the Ras-binding domain of PI3K1 suggests that Ras is activated throughout vesicle formation. Binding assays show that RasG and RasS interact most strongly with PI3K1/2 and PI3K4 and single mutants of either Ras have severe macropinocytosis defects. Thus, the fundamental function of PI3-kinases in growing Dictyostelium cells is in macropinocytosis where they have two distinct functions, supported by at least two separate Ras proteins. Submitted by Oliver Hoeller [oliver.hoeller@ucsf.edu] ============================================================== [End dictyNews, volume 39, number 18]