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dictyNews Volume 21 Number 16
Dicty News
Electronic Edition
Volume 21, number 16
November 21, 2003
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 Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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Two Dictyostelium Orthologs of the Prokaryotic Cell Division Protein,
FtsZ, Localize to Mitochondria and Are Required for the
Maintenance of Normal Mitochondrial Morphology
Paul R. Gilson,1* Xuan-Chuan Yu,2 Dale Hereld,2 Christian Barth,3 Amelia
Savage,1
Ben R. Kiefel,1 Sui Lay,3 Paul R. Fisher,3 William Margolin,2 and Peter L.
Beech1
Centre for Cellular and Molecular Biology, School of Biological and
Chemical Sciences, Deakin University, Victoria 3125,1 and
Department of Microbiology, La Trobe University, Bundoora, Victoria 3083,3
Australia, and Department of Microbiology and Molecular Genetics,
University of Texas Medical School, Houston, Texas 770302
Eukaryotic Cell, in press
In bacteria, the protein FtsZ is the principal component of a ring that
constricts the cell at division. Though all mitochondria probably arose
through a single, ancient bacterial endosymbiosis, the mitochondria of
only certain protists appear to have retained FtsZ and the protein is
absent from the mitochondria of fungi, animals and higher-plants. We
have investigated the role FtsZ plays in mitochondrial division in the
genetically-tractable protist Dictyostelium discoideum, which encodes
two nuclear-encoded FtsZs, FszA and FszB, that are targeted to the
inside of mitochondria. In most wild-type amoebae, the mitochondria
are spherical or rod-shaped, but in fsz-null mutants they become
elongated into tubules - indicating a decrease in mitochondrial
division has occurred. In support of this role in organelle division,
antibodies to FszA, and FszA-GFP, show belts and puncta at multiple
places along the mitochondria, which may define future or recent sites
of division. FszB-GFP, in contrast, locates to an electron-dense,
sub-mitochondrial body usually located at one end of the organelle
but how it functions during division is unclear. This is the first
demonstration of two differentially localised FtsZs within the one
organelle, and points to a divergence in the roles of these two
proteins.Ê
Submitted by: Paul Gilson [gilson@wehi.edu.au]
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Surrogate hosts: protozoa and invertebrates as models for studying
pathogen-host interactions
Michael Steinert, Matthias Leippe, Thomas Roeder
Int. J. Med. Microbiol., in press
Animal models, primary cell culture systems and permanent cell lines
have provided important information on virulence properties of
pathogenic microorganisms. Recently, it has been shown that some
inherent limitations of such models can be circumvented by using
non-vertebrate hosts such as Caenorhabditis elegans, Drosophila
melanogaster and Dictyostelium discoideum. These new models are helpful
to follow infection processes at the molecular level. Persuasive support
comes from the fact that processes such as phagocytosis, cell signaling
or innate immunity can be studied in these surrogate hosts. This review
describes the establishment and application of each of the three
aforementioned and genetically tractable hosts. In addition, we will
report on a number of approaches that led to the identification of host
cell factors which influence the susceptibility of the hosts to
infection.
Submitted by: Matthias Leippe [mleippe@zoologie.uni-kiel.de]
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The Ca2+/Calcineurin-regulated cup Gene Family in Dictyostelium discoideum
and Its Possible Involvement in Development
Barrie Coukell, Yi Li, John Moniakis and Anne Cameron
Department of Biology,
York University,
4700 Keele, St.,
Toronto, ON, M3J 1P3, CANADA
Eukaryotic Cell, in press
Changes in free intracellular Ca2+ are thought to regulate several
major processes during Dictyostelium development including cell
aggregation and cell type-specific gene expression, but the mechanisms
involved are unclear. To learn more about Ca2+ signalling and Ca2+
homeostasis in this organism, we used suppression subtractive
hybridization to identify genes up-regulated by high extracellular Ca2+.
Unexpectedly, many of the genes identified belong to a novel gene family
(termed cup) with seven members. In vegetative cells, the cup genes were
up-regulated by high Ca2+, but not by other ions or by heat, oxidative or
osmotic stress. cup induction by Ca2+ was blocked completely by
inhibitors of calcineurin and protein synthesis. In developing cells, cup
expression was high during aggregation and late development, but low
during the slug stage. This pattern correlates closely with reported
levels of free intracellular Ca2+ during development. The cup gene
products are highly homologous, acidic proteins possessing putative ricin
domains. BLAST searches failed to reveal homologs in other organisms but
Western analyses suggested that cup-like proteins might exist in certain
other cellular slime mold species. Localization experiments indicated
that cup proteins are primarily cytoplasmic, but become cell
membrane-associated during Ca2+ stress and cell aggregation. When cup
expression was down-regulated by antisense RNA, the cells failed to
aggregate. However, this developmental block was overcome by partially
up-regulating cup expression. Together, these results suggest that the
cup proteins in Dictyostelium might play an important role in
stabilizing/regulating the cell membrane during Ca2+ stress and/or certain
stages of development.
Submitted by: Barrie Coukell [bcoukell@yorku.ca]
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Defect in Peroxisomal Multifunctional Enzyme MFE1 Affects cAMP Relay in
Dictyostelium
#1Satomi Matsuoka, #$1Hidekazu Kuwayama, 1Daisuke Ikeno, 2Masakazu Oyama,
and 1*Mineko Maeda
Develop. Growth Differ., in press
We have previously reported that cells of Dictyostelium discoideum lacking
the fatty acid oxidation enzyme MFE1 accumulate excess cyclopropane fatty
acids from ingested bacteria. Cells in which mfeA- is disrupted fail to
develop when grown in association with bacteria but form normal fruiting
bodies when grown in axenic media. Bacterially grown mfeA- cells express the
genes for the cAMP receptor (carA) and adenylyl cyclase (acaA) but fail to
respond to a cAMP pulse by synthesis of additional cAMP which normally
relays the signal. Moreover, they do not accumulate the adhesion protein,
gp80, which is encoded by the cAMP-induced gene, csaA. As a consequence they
do not acquire developmentally regulated EDTA-resistant cell-cell adhesion.
When mutant cells are mixed with wild type cells and allowed to develop
together, they co-aggregate and differentiate into both spores and stalk
cells. Thus, most of the developmental consequences of excess cyclopropane
fatty acids appear to result from impaired cAMP relay.
Submitted by: Mineko Maeda [mmaeda@bio.sci.osaka-u.ac.jp]
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[End Dicty News, volume 21, number 16]
