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dictyNews Volume 34 Number 14
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
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Abstracts
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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]
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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]
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[End dictyNews, volume 34, number 14]
