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dictyNews Volume 25 Number 06
Dicty News
Electronic Edition
Volume 25, number 6
September 16, 2005
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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Function and mechanism of action of Dictyostelium Nramp1 (Slc11a1) in
bacterial infection
Barbara Peracino, Carina Wagner*, Alessandra Balest, Alessandra Balbo,
Barbara Pergolizzi, Angelika A. Noegel¤, Michael Steinert* and
Salvatore Bozzaro
Traffic, in press
Dictyostelium amoebae are professional phagocytes, which ingest bacteria
as the principal source of food. We have cloned the Dictyostelium homologue
of human Nramp1 (Slc11a1), an endo-lysosomal membrane protein that confers
on macrophages resistance to infection by a variety of intracellular
bacteria and protozoa. The Dictyostelium Nramp1 gene encodes a protein
of 53kDa with 11 putative transmembrane domains. The Nramp1 gene is
transcribed during the growth-phase and down regulated to barely
detectable levels upon starvation. To gain insights into their
intracellular localization, Nramp1 or the vatB subunit of the V-H+ATPase
were fused with GFP and expressed in cells. GFP-vatB was inserted in
membranes of all acidic compartments and the contractile vacuole network,
and decorated macropinosomes and phagosomes. GFP-Nramp1 decorated
macropinosomes and phagosomes, in addition to intracellular vesicular
compartments positive for endosomal SNARE protein Vti1 or vacuolin, a
marker of the exocytic pathway. Nramp1 disruption generated mutants
that were more permissive hosts than wild-type cells for intracellular
growth of L. pneumophyla and M. avium. Nramp1 overexpression protected
cells from L. pneumophila infection. Evidence is provided that Nramp1
transports metal cations out of the phago-lysosome in an ATP-dependent
process, and that L. pneumophila and M. avium use different mechanisms to
neutralize Nramp1 activity.
Submitted by: Salvatore Bozzaro [salvatore.bozzaro@unito.it]
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Dictyostelium transcriptional host cell response upon infection with
Legionella
Patrick Farbrother1, Carina Wagner2, Jianbo Na1, Budi Tunggal1, Takahiro
Morio3, Hideko Urushihara3, Yoshimasa Tanaka3, Michael Schleicher4, Michael
Steinert2 and Ludwig Eichinger1
1 Institut fr Biochemie I, Medizinische Fakultt, Universitt zu Kln,
Joseph-Stelzmann-Str. 52, D-50931 Kln
2 Institut fr Molekulare Infektionsbiologie, Universitt Wrzburg,
Rntgenring 11, D-97070 Wrzburg
3 Graduate School of Life and Environmental Sciences, University of
Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
4 Institut fr Zellbiologie, Medizinische Fakultt,
Ludwig-Maximilians-Universitt Mnchen, D-80336 Mnchen
Cellular Microbiology, in press
Differential gene expression of Dictyostelium discoideum after infection
with Legionella pneumophila was investigated using DNA-microarrays.
Investigation of a 48-hour time course of infection revealed several
clusters of co-regulated genes, an enrichment of preferentially up- or
down-regulated genes in distinct functional categories and also showed that
most of the transcriptional changes occurred 24 hours after infection. A
detailed analysis of the 24-hour time point post-infection was performed in
comparison to three controls, uninfected cells and co-incubation with L.
hackeliae and L. pneumophila DdotA. 131 differentially expressed D.
discoideum genes were identified as common to all three experiments and are
thought to be involved in the pathogenic response. Functional annotation of
the differentially regulated genes revealed that apart from triggering a
stress response Legionella apparently not only interferes with
intracellular vesicle fusion and destination but also profoundly influences
and exploits the metabolism of its host. For some of the identified genes
e.g. RtoA involvement in the host response has been demonstrated in a
recent study, for others such a role appears plausible. The results provide
the basis for a better understanding of the complex host-pathogen
interactions and for further studies on the Dictyostelium response to
Legionella infection.
Submitted by: Ludwig Eichinger [ludwig.eichinger@uni-koeln.de]
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Comparative genomics of Dictyostelium discoideum and Entamoeba histolytica
Ludwig Eichinger and Angelika A Noegel
Centre for Biochemistry and Centre for Molecular Medicine Cologne,
Medical Faculty, University of Cologne, Joseph-Stelzmann-Str. 52,
50931 Kln, Germany
Curr. Opin. Microbiol., in press
Amoebozoa represent one of the earliest branches from the last common
ancestor of all eukaryotes and contain some of the most dangerous human
pathogens. Two amoebozoan genomes - from the model organism Dictyostelium
discoideum and the
human pathogen Entamoeba histolytica - have been published this year. Owing
to their high A+T content, both genomes were difficult to sequence. In
addition to nine amoebozoan expressed sequence tag projects, efforts are
underway for comparative sequencing of four additional Entamoeba species.
The completed genome sequences of D. discoideum and E. histolytica revealed
unusual telomere structures, a high percentage of repetitive elements and a
remarkably high gene content that is close to the one of Drosophila
melanogaster. Finally, both organisms are brilliant examples of the
influence of the lifestyle of an organism on its genome.
Submitted by: Ludwig Eichinger [ludwig.eichinger@uni-koeln.de]
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[End Dicty News, volume 25, number 6] 
