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dictyNews Volume 25 Number 01
Dicty News
Electronic Edition
Volume 25, number 1
July 8, 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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The Dictyostelium Genome Encodes Numerous RasGEFs with Multiple
Biological Roles
Andrew Wilkins2*, Karol Szafranski1*, Derek J. Fraser3, Deenadayalan
Bakthavatsalam4, Rolf Mueller4, Paul R. Fisher3, Gernot Gloeckner1,
Ludwig Eichinger4, Angelika Noegel4 and Robert H. Insall2,5
1 Genome Analysis, Institute for Molecular Biotechnology,
Beutenbergstr. 11, D-07745 Jena, Germany
2 School of Biosciences, University of Birmingham, Birmingham B15 2TT,
UK
3 La Trobe University, VIC 3086, Australia
4 Centre for Biochemistry and Centre for Molecular Medicine Cologne,
Medical Faculty, University of Cologne, Joseph-Stelzmann-Str. 52,
50931 Cologne, Germany
5 Corresponding author
BACKGROUND
Dictyostelium discoideum is a eukaryote with a simple lifestyle and a
relatively small genome whose sequence has been fully determined. It
is widely used for studies on cell signalling, movement and multicellular
development. Ras nucleotide exchange factors (RasGEFs) are the proteins
which activate Ras and thus lie near the top of multiple signalling
pathways. They are particularly important for signalling in development
and chemotaxis in many organisms including Dictyostelium.
RESULTS
We have searched the genome for sequences encoding RasGEFs. Despite its
relative simplicity, we find that the Dictyostelium genome encodes at
least 25 RasGEFs, with a few other genes encoding only parts of the RasGEF
consensus domains. All appear to be expressed at some point in development.
The 25 genes include a wide variety of domain structures, most of which have
not been seen in other organisms. The LisH domain, which is associated with
microtubule binding, is seen particularly frequently; other domains which
confer interactions with the cytoskeleton are also common. Disruption of a
sample of the novel genes reveals that many have clear phenotypes, including
altered morphology and defects in chemotaxis, slug phototaxis and thermotaxis.
CONCLUSIONS
These results suggest that the unexpectedly large number of RasGEF genes
reflects an evolutionary expansion of the range of Ras signalling rather
than functional redundancy or the presence of multiple pseudogenes.
Submitted by: Robert Insall [r.h.insall@bham.ac.uk]
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Dictyopyrones, novel a-pyronoids isolated from Dictyostelium spp., promote
stalk cell differentiation in Dictyostelium discoideum
Akiko Arai, Yukino Goto, Aiko Hasegawa, Kohei Hosaka, Haruhisa Kikuchi,
Yoshiteru Oshima, Susumu Tanaka and Yuzuru Kubohara*
*Gunma University IMCR, Maebshi 371-8512, Japan
Differentiation, in press
Dictyopyrones A and B (DpnA and DpnB) whose function(s) is not known were
isolated from fruiting bodies of Dictyostelium discoideum. In the present
study, to assess their function(s), we examined the effects of Dpns on
in vitro cell differentiation in D. discoideum monolayer cultures with cAMP.
Dpns at 1-20 microM promoted stalk cell formation to some extent in the
wild-type strain V12M2. Although Dpns by themselves could hardly induce
stalk cell formation in a DIF-deficient strain HM44, both of them
dose-dependently promoted DIF-1-dependent stalk cell formation in the
strain. In the sporogenous strain HM18, Dpns at 1-20 microM suppressed
spore formation and promoted stalk cell formation in a dose-dependent
manner. Analogs of Dpns were less effective in affecting cell
differentiation in both HM44 and HM18 cells, indicating that the activity of
Dpns should be chemical structure-specific. It was also shown that DpnA at
2-20 microM dose-dependently suppressed spore formation induced with 8-bromo
cAMP and promoted stalk cell formation in V12M2 cells. Interestingly, it
was shown by the use of RT-PCR that DpnA at 10 microM slightly promoted both
prespore- and prestalk-specific gene expressions in an early phase of V12M2
and HM18 in vitro differentiation. The present results suggest that Dpns may
have functions 1) to promote both prespore and prestalk cell differentiation
in an early stage of development and 2) to suppress spore formation and
promote stalk cell formation in a later stage of development in D. discoideum.
Submitted by: Yuzuru Kubohara <kubohara@showa.gunma-u.ac.jp]
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CAP is essential for the functioning of the endo-lysosomal system and
provides a link to the actin cytoskeleton
Hameeda Sultana, Francisco Rivero, Rosemarie Blau-Wasser, Stephan Schwager,
Alessandra Balbo, Salvatore Bozzaro, Michael Schleicher, Angelika A. Noegel
Traffic (accepted)
Data from mutant analysis in yeast and Dictyostelium indicate a role for the
cyclase-associated protein (CAP) in endocytosis and vesicle transport. We
have used genetic and biochemical approaches to identify novel interacting
partners of Dictyostelium CAP to help explain its molecular interactions in
these processes. CAP associates and interacts with subunits of the highly
conserved vacuolar H+-ATPase (V-ATPase) and colocalizes to some extent with
the V-ATPase. Furthermore, CAP is essential for maintaining the structural
organization, integrity and functioning of the endo-lysosomal system as
distribution and morphology of V-ATPase and Nramp1 decorated membranes were
disturbed in a CAP mutant (CAP bsr) accompanied by an increased endosomal pH.
Moreover, concanamycin A (CMA), a specific inhibitor of the V-ATPase, had a
more severe effect on CAP bsr than on wild type cells and the mutant did not
show adaptation to the drug. Also, the distribution of GFP-CAP was affected
upon CMA treatment in the wild type and recovered after adaptation.
Distribution of the V-ATPase in CAP bsr was drastically altered upon
hypo-osmotic shock and growth was slower and reached lower saturation
densities in the mutant under hyper-osmotic conditions. Taken together, our
data unravel a link of CAP with the actin cytoskeleton and endocytosis and
suggest that CAP is an essential component of the endo-lysosomal system in
Dictyostelium.
Submitted by: Angelika Noegel [noegel@uni-koeln.de]
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[End Dicty News, volume 25, number 1] 
