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dictyNews Volume 25 Number 07
Dicty News
Electronic Edition
Volume 25, number 7
September 30, 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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Ammonium transporter C of Dictyostelium discoideum is required for correct
prestalk gene expression and for regulating the choice between slug migration
and culmination
Janet H. Kirsten, Yanhua Xiong, Andrew J. Dunbar, Meena Rai, Charles K.
Singleton *
Department of Biological Sciences, Vanderbilt University, VU Station
B 351634, Nashville TN 37235-1634, USA
Developmental Biology, in press.
Ammonium transporter C (AmtC) is one of three transporters in Dictyostelium
that have been proposed to regulate entry and exit of ammonia in a cell type
dependent manner and to mediate ammonia signaling. Previous work demonstrated
that disruption of the amtC gene results in a slugger phenotype in which the
cells remain as migrating slugs when they should form fruiting bodies. More
detailed studies on the null strain revealed that differentiation of prestalk
cell types was delayed and maintenance of prestalk cell gene expression was
defective. There was little orno expression of ecmB, a marker for the
initiation of culmination. Normal expression of CudA, a nuclear protein
required for culmination, was absent in the anterior prestalk zone. The
absence of CudA within the tip region was attributable to the lack of
adenylyl cyclase A mRNA in the slug tips. Disruption of the histidine kinase
gene dhkC in the amtC null strain restored STATa and CudA expression and the
ability to culminate. The results suggest that the lack of nuclear t
ranslocation of STATa results from low cAMP due to a misregulated and
overactive DhkC phosphorelay in the amtC null strain.
Submitted by: Charles Singleton [charles.k.singleton@vanderbilt.edu]
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Role of calcium-dependent actin-bundling proteins: characterization of
Dictyostelium mutants lacking fimbrin and the 34 kDa protein
Claudia Pikzack(1), Josef Prassler(2), Ruth Furukawa(3), Marcus Fechheimer(3)
and Francisco Rivero(1)
(1) Zentrum fr Biochemie and Zentrum fr Molekulare Medizin, Medizinische
Fakultt, Universitt zu Kln, Joseph-Stelzmann-Str. 52, 50931 Kln, Germany
(2) Max-Planck-Institut fr Biochemie, Am Klopferspitz 18a,
82152 Martinsried, Germany
(3) Department of Cellular Biology, University of Georgia, Athens,
GA 30602, USA
Cell Motility and the Cytoskeleton, in press
Dictyostelium discoideum two abundant proteins display calcium-regulated
bundling activity, fimbrin and the 34 kDa protein (ABP34). Using a GFP
fusion we observed transient localization of fimbrin at the phagocytic cup
and macropinosomes. The distribution of truncated constructs encompassing t
he EF hands and the first actin-binding domain (EA1) or both actin-binding
domains devoid of EF hands (A1A2) was indistinguishable from that of the
full length protein. The role of fimbrin and a possible functional overlap
with ABP34 was investigated in fim- and double 34-/fim- mutants. Except for
a moderate cell size defect, fim- mutants did not show defects in growth,
endocytosis, exocytosis and chemotaxis. Double mutants were characterized by
a small cell size and a defect in morphogenesis resulting in small fruiting
bodies and a low spore yield. The cell size defect could not be overcome by
expression of fimbrin fragments EA1 or A1A2, suggesting that both bundling
activity and regulation by calcium are important. Induction of filopod
formation in 34-/fim- cells was not impaired, indicating that both proteins
are dispensable for this process. We searched in the Dictyostelium genome
database for fimbrin-like proteins that could compensate for the fimbrin
defect and identified three unconventional fimbrins and two more proteins
with actin-binding domains of the type present in fimbrins.
Submitted by: Francisco Rivero [francisco.rivero@uni-koeln.de]
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Specific host genes required for the killing of Klebsiella bacteria by
phagocytes.
Mohammed Benghezal, Marie-Odile Fauvarque, Rgis Tournebize, Romain Froquet,
Anna Marchetti, Evelyne Bergeret, Bernard Lardy, Grard Klein, Philippe
Sansonetti, Steve J. Charette, Pierre Cosson
Cellular Microbiology, in press
The amoeba Dictyostelium discoideum shares many traits with mammalian
macrophages, in particular the ability to phagocytose and kill bacteria. In
response, pathogenic bacteria use conserved mechanisms to fight amoebae and
mammalian phagocytes. Here we developed an assay using Dictyostelium to
monitor phagocyte-bacteria interactions. Genetic analysis revealed that the
virulence of Klebsiella pneumoniae measured by this test is very similar to
that observed in a mouse pneumonia model. Using this assay, two new host
resistance genes (PHG1 and KIL1) were identified and shown to be involved
in intracellular killing of K. pneumoniae by phagocytes. Phg1 is a member of
the 9TM family of proteins, and Kil1 is a sulfotransferase. The loss of PHG1
resulted in Dictyostelium susceptibility to a small subset of bacterial
species including K. pneumoniae. Remarkably, Drosophila mutants deficient for
PHG1 also exhibited a specific susceptibility to K. pneumoniae infections.
Systematic analysis of several additional Dictyostelium mutants created a
two-dimensional virulence array, where the complex interactions between host
and bacteria are visualized.
Submitted by: Pierre Cosson [Pierre.Cosson@medecine.unige.ch]
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[End Dicty News, volume 25, number 7] 
