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dictyNews Volume 21 Number 08
Dicty News
Electronic Edition
Volume 21, number 8
September 12, 2003
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu.
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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A Dictyostelium Long Chain Fatty Acyl Coenzyme A-Synthetase mediates fatty
acid retrieval from endosomes
Katharina von Loehneysen, Nadine Pawolleck, Harald Ruehling, and Markus Maniak
Abt. Zellbiologie, Universitaet Kassel, Heinrich-Plett-Str. 40, 34142 Kassel,
Germany
Eur. J. Cell Biol., in press
We have identified a subset of Dictyostelium endosomes that carry a Long Chain
Fatty Acyl Coenzyme A-Synthetase (LC-FACS 1) on their cytosolic surface.
Immunofluorescence studies and observations using GFP-fusion proteins
collectively suggest that LC-FACS 1 associates with endosomes a few minutes
after their formation, remains bound through the acidic phase of endocytic
maturation and dissociates early in the phase where the endosomal content is
neutralised prior to exocytosis. Mutants in the fcsA gene, encoding the
LC-FACS 1 protein, were constructed by homologous recombination. These cells
show a strong defect in the intracellular accumulation of fatty acids, either
taken up together with the liquid medium or bound to the surface of particles.
Because the mutant cells are otherwise fully competent for macropinocytosis
and phagocytosis, we conclude that the LC-FACS 1 protein mediates the
retrieval of fatty acids from the lumen of endosomes into the cytoplasm.
Submitted by: Markus Maniak [maniak@uni-kassel.de]
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A Coat of Filamentous Actin Prevents Clustering of Late Endosomal Vacuoles
in Vivo
Anja Drengk, Juergen Fritsch, Christian Schmauch, Harald Ruehling,
and Markus Maniak
Abteilung Zellbiologie and Center for Interdisciplinary Nanostructure Science
and Technology (CINSaT)
Universitaet Kassel, Heinrich Plett Str. 40, 34132 Kassel, Germany
Current Biology, in press
Many steps of endocytosis and endosomal trafficking depend on the actin
cytoskeleton. A lot of details are now known for the internalisation step at
the plasma membrane [1, 2] and a number of experiments implicate filamentous
actin in subsequent steps like propulsion through the cytoplasm [3, 4],
fusion of phagosomes with early endosomes [5], and traffic from early to late
endosomes [6, 7]. In vitro studies using endosomes from mammalian cells and
vacuoles from yeast suggest a role for actin in the process of membrane fusion
[8, 9]. Here, we investigate the function of the actin coat that surrounds
a late endocytic compartment in Dictyostelium cells [10]. Treating cells with
the actin sequestering drug latrunculin leads to the aggregation of these
endosomes into large, grape-like clusters and provokes a complete block of
endocytic marker progression. In addition the cells round up and stop moving.
To avoid that all actin assemblies in the cell are perturbed simultaneously,
we constructed a hybrid protein to specifically target cofilin, an actin
depolymerising protein, to the late endosomes. Again, the endosomal
compartments lost their actin coats and aggregated, but these cells remained
morphologically normal, and no kinetic effect on the trafficking of endocytic
marker was apparent. These results demonstrate that an actin coat can prevent
the clustering of endosomes, which could be a safeguard mechanism precluding
their docking and fusion. In addition, our targeting approach provides a means
to specifically study the function of the cytoskeleton in one subcellular
location without interfering with other actin functions in the cell.
Submitted by: Markus Maniak [maniak@uni-kassel.de]
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A Cell-Adhesion Pathway Regulates Intercellular Communication During
Dictyostelium Development
Kirsten Kibler, Jessica Svetz, Tu-Lan Nguyen, Chad Shaw and Gad Shaulsky
Graduate Program in Developmental Biology
Department of Molecular and Human Genetics
Baylor College of Medicine
One Baylor Plaza
Houston, TX 77030
USA
Developmental Biology, in press
Cell adhesion molecules play an important physical role in shaping the
structure of multicellular organisms. Recent studies show that they also
play a role in intracellular and intercellular signaling. We describe a cell
adhesion pathway that is mediated by the intercellular communication genes
comC, lagC, and lagD during Dictyostelium development. Disruptions of these
genes result in strains that are unable to generate spores when developed in
a pure population but are capable of sporulation when developed in chimerae
with wild type cells. In contrast, any pair-wise chimera of the three
mutants fails to form spores. We postulate that the wild type cells supply
the mutant cells with a signal that partially rescues their sporulation.
We also propose that the three mutants are deficient in the production of
that signal, suggesting that the three genes function in one signaling
pathway. In support of that notion, the mutant cells share common non
cell-autonomous prespore and prestalk-specific defects and a common pattern
of developmental progression and regression. We provide transcriptional
and functional evidence for a network in which comC inhibits lagC and
activates lagD expression, lagC and lagD are mutually inductive, and the
cell adhesion gene lagC is the terminal node in this signaling network.
Submitted by: Gad Shaulsky [gadi@bcm.tmc.edu]
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Biochemical Basis of the high resistance to oxidative stress in Dictyostelium
discoideum
Bandhana Katoch and Rasheedunnnisa Begum
Department of Biochemistry, M.S.University of Baroda
Gujarat
India
Journal of Biosciences, Vol.28, No.5, Sep 2003, 581-588
Aerobic organisms experience oxidative stress due to generation of reactive
oxygen species during normal aerobic metabolism. In addition, several
chemicals also generate reactive oxygen species which induce oxidative
stress. Thus, oxidative stress constitutes a major threat to organisms
living in aerobic environments. Programmed cell death or apoptosis is a
physiological mechanism of cell death, that probably evolved with
multicellularity, and is indispensible for normal growth and development.
Dictyostelium discoideum, an eukaryotic developmental model, shows both
unicellular and multicellular forms in its life cycle and exhibits appparent
caspase-independent programmed cell death, and also shows high resisitance
to oxidative stress. An attempt has been made to investigate the biochemical
basis for high resistance of D.discoideum cell death induced by different
oxidants. Dose-dependent induction of cell death by exogenous addition of
hydrogen peroxide(H2O2), in situ generation of H2O2 by hydroxylamine and
nitirc oxide (NO) generation by sodium nitoprusside treatment in
Dictyostelium discoideum were studied. The AD50 doses(concentration of
oxidants causing 50% of cells to die) after 24 hours of treatment were
found to be 0.45mM, 4mM and 1mM, respectively. Studies on enzymatic
antioxidant status of D.discoideum when subjected to oxidative stress, NO
and nutrient stress reveal that superoxode dismutase and catalase were
unchanged; a significant induction of glutathione peroxodase was observed.
Interestingly, oxidative stress-induced lipid membrane peroxidatiove damage
could not be detected.The result shed on the biochemical basis for the
observed high resisitance to oxidative stress in D.discoideum.
Submitted by: Bandhana Katoch and Rasheedunnisa Begum [rasheeda@wilnetonline.net]
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[End Dicty News, volume 21, number 8]
