dictyNews Electronic Edition Volume 34, number 14 May 7, 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 ========= Complex genotype interactions influence social fitness during the developmental phase of the social amoeba Dictyostelium discoideum Neil J. Buttery1, Christopher R. L. Thompson1,* and Jason B. Wolf2,* 1Faculty of Life Sciences, The University of Manchester, Michael Smith Building, Oxford Rd, Manchester, M13 9PT, UK. 2Departmemt of Biology & Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK. *Corresponding authors Journal of Evolutionary Biology, in press Abstract: When individuals interact, phenotypic variation can be partitioned into direct genetic effects (DGEs) of the individuals’ own genotypes, indirect genetic effects (IGEs) of their social partners’ genotypes and epistatic interactions between the genotypes of interacting individuals (‘genotype-by-genotype (G×G) epistasis’). These components can all play important roles in evolutionary processes, but few empirical studies have examined their importance. The social amoeba Dictyostelium discoideum provides an ideal system to measure these effects during social interactions and development. When starved, free-living amoebae aggregate and differentiate into a multicellular fruiting body with a dead stalk that holds aloft viable spores. By measuring interactions among a set of natural strains we quantify DGEs, IGEs and G×G epistasis affecting spore formation. We find that DGEs explain most of the phenotypic variance (57.6%) while IGEs explain a smaller (13.3%) but highly significant component. Interestingly, G×G epistasis explains nearly a quarter of the variance (23.0%), highlighting the complex nature of genotype interactions. These results demonstrate the large impact that social interactions can have on development and suggest that social effects should play an important role in developmental evolution in this system. Submitted by Chris Thompson [christopher.thompson@manchester.ac.uk] -------------------------------------------------------------------------------- Unconventional secretion of AcbA in Dictyostelium discoideum through a vesicular intermediate. Matthew Cabral, Christophe Anjard, Vivek Malhotra, William F. Loomis, and Adam Kuspa Verna and Marrs McLean Department Biochemistry and Molecular Biology and Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA, 77030. Center for Molecular Genetics, Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093. Eukaryotic Cell, in press The acyl-CoA binding protein, AcbA, is secreted unconventionally and processed into SDF-2, a peptide that coordinates sporulation in Dictyostelium. We report that AcbA is localized in vesicles that accumulate in the cortex of prespore cells just prior to sporulation. These vesicles are not observed after cells are stimulated to release AcbA, but remain visible after stimulation in cells lacking the Golgi reassembly stacking protein (GRASP). Acyl-CoA binding is required for the inclusion of AcbA in these vesicles, and the secretion of AcbA requires N-ethylmaleimide sensitive factor (NSF). About 1 percent of the total cellular AcbA can be purified within membrane-bound vesicles. The yield of vesicles decreases dramatically when purified from wild-type cells that were stimulated to release AcbA, whereas the yield from GRASP mutant cells was only modestly altered by stimulation. We suggest these AcbA-containing vesicles are secretion intermediates and that GRASP functions at a late step leading to the docking/fusion of these vesicles at the cell surface. Submitted by Adam Kuspa [akuspa@bcm.edu] -------------------------------------------------------------------------------- Genetic evidence for concerted control of actin dynamics in cytokinesis, endocytic traffic, and cell motility by coronin and Aip1 Hellen C. Ishikawa-Ankerhold1, Günther Gerisch1, and Annette Müller-Taubenberger2 1 Max Planck Institute for Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany 2 Institute for Cell Biology and Center for Integrated Protein Science Munich (CIPSM), Ludwig Maximilians University Munich, Schillerstr. 42, 80336 München, Germany Cytoskeleton, in press Coronin and actin-interacting protein 1 (Aip1) are actin-binding proteins that by different mechanisms inhibit actin polymerization or enhance the disassembly of actin filaments. Cells of Dictyostelium discoideum lacking both proteins are retarded in growth and early development and often fail to proceed to fruiting body formation. Coronin/Aip1-null cells show numerous surface protrusions enriched in filamentous actin and cofilin. We show that the double-null cells are characterized by an increase in filamentous actin that causes a thickening of the cell cortex. This imbalance has severe consequences for processes that rely on the dynamic reorganization of the actin cytoskeleton as cell motility, cytokinesis and endocytosis. Although cell motility is considerably slowed down, the double-mutant cells are still capable of orientating in a gradient of chemoattractant. The cytokinesis defect is caused by the lack of proper cleavage furrow formation, a defect that is partially rescued by low concentrations of latrunculin A, an inhibitor of actin polymerization. Furthermore, we demonstrate that the disassembly of the actin coat after phagocytic or macropinocytic uptake is significantly delayed in the double-mutant cells. Our results prove that coronin and Aip1 are important effectors that act together in maintaining the balance of actin polymerization and depolymerization in living cells. Submitted by Annette Müller-Taubenberger [amueller@lrz.uni-muenchen.de] ============================================================== [End dictyNews, volume 34, number 14]