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dictyNews Volume 22 Number 17
Dicty News
Electronic Edition
Volume 22, number 17
June 25, 2004
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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Extracellular matrix family proteins that are potential targets of Dd-STATa
in Dictyostelium discoideum
Nao Shimada1, Keiko Nishio2, Mineko Maeda2, Hideko Urushihara3 and
Takefumi Kawata1, 4
1Department of Biology, Faculty of Science, Toho University, 2-2-1 Miyama,
Funabashi, Chiba 274-8510, JAPAN
TEL & FAX: 81-47-472-5156, E-mail: tkawata@bio.sci.toho-u.ac.jp
2 Department of Biology, Graduate School of Science, Osaka University,
Toyonaka, Osaka 560-0043
3 Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572
4 Corresponding author
J. Plant Res., in press
Dd-STATa is a functional Dictyostelium homologue of metazoan STAT (signal
transducers and activators of transcription) proteins, which is activated
by cAMP and is thereby translocated into the nuclei of anterior tip cells
of the prestalk region of the slug. By using in situ hybridization analyses,
we found that the SLF308 cDNA clone, which contains the ecmF gene that
encodes a putative extracellular matrix protein and is expressed in the
anterior tip cells, was greatly down-regulated in the Dd-STATa-null mutant.
Disruption of the ecmF gene, however, resulted in almost no phenotypic
change. The absence of any obvious mutant phenotype in the ecmF-null mutant
could be due to a redundancy of similar genes. In fact, a search of the
Dictyostelium whole genome database demonstrates the existence of additional
16 homologues, all of which contain a cellulose-binding module. Among these
homologues, four genes show Dd-STATa-dependent expression, while the others
were Dd-STATa-independent. We discuss the potential role of Dd-STATa in
morphogenesis via its effect on the interaction between cellulose and these
extracellular matrix family proteins.
Submitted by: Takefumi Kawata [tkawata@bio.sci.toho-u.ac.jp]
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GSK-3 is a multi-functional regulator of Dictyostelium development
Christina Schilde, Tsuyoshi Araki, Hazel Williams*, Adrian Harwood*,
and Jeffrey G. Williams
School of Life Sciences, Wellcome Trust Biocentre, University of Dundee,
Dundee DD1 5EH, UK
* MRC Laboratory for Molecular Cell Biology & Dept of Biology, University
College, Gower St, London WC1E 6BT
Development, in press
Glycogen Synthase Kinase-3 (GSK-3) is a central regulator of metazoan
development and the Dictyostelium GSK-3 homologue, GskA, also controls
cellular differentiation. The originally derived gskA null mutant exhibits
a severe pattern formation defect. It forms very large numbers of pre-basal
disc cells at the expense of the prespore population. This defect arises
early during multicellular development, making it impossible to examine
later functions of GskA. We report the analysis of a gskA null mutant,
generated in a different parental strain, which proceeds through development
to form mature fruiting bodies. In this strain, Ax2/gskA-, early development
is accelerated and slug migration greatly curtailed. In a monolayer assay of
stalk cell formation, the Ax2/gskA- strain is hyper-sensitive to the stalk
cell inducing action of DIF-1 but largely refractory to the repressive
effect exerted by extracellular cAMP. During normal development apically
situated prestalk cells express the ecmB gene just as they commit
themselves to stalk cell differentiation. In the Ax2/gskA- mutant ecmB is
expressed throughout the prestalk region of the slug, suggesting that GskA
forms part of the repressive signalling pathway that prevents premature
commitment to stalk cell differentiation. GskA may also play an inductive
developmental role, because micro-array analysis identifies a large gene
family, the 2C family, that require gskA for optimal expression. These
observations show that GskA functions throughout Dictyostelium development,
to regulate several key aspects of cellular patterning.
Submitted by: Jeff Williams [j.g.williams@dundee.ac.uk]
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Chemotaxis: signalling the way forward
Peter J.M. Van Haastert1 and Peter N Devreotes2
1Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG
Groningen, the Netherlands
2 Department of Cell Biology , Johns Hopkins University School of Medicine,
725 N. Wolfe St., 114 WBSB Baltimore, MD 21205, USA
Nature Reviews Molecular Cell Biology, in press
During random locomotion, human neutrophils and Dictyostelium discoideum
amoebae repeatedly extend and retract cytoplasmic processes. During directed
cell migration ? chemotaxis ? these pseudopodia form predominantly at the
leading edge in response to the local accumulation of certain signalling
molecules. Concurrent changes in actin and myosin enable the cell to move
towards the stimulus. Recent studies are beginning to identify an intricate
network of signalling molecules that mediate these processes, and how these
molecules become localized in the cell.
Submitted by: Peter van Haastert" <P.J.M.van.Haastert@chem.rug.nl
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CbfA, the C-module DNA-binding factor, plays an essential role in the
initiation of development of Dictyostelium
Thomas Winckler(1), Negin Iranfar(2), Peter Beck(1), Ingo Jennes(1),
Oliver Siol(1), Unha Baik(1), William F. Loomis(2) and Theodor Dingermann(1)
1 Institut fuer Pharmazeutische Biologie, Universitaet Frankfurt
(Biozentrum), D-60439 Frankfurt am Main (Germany)
2 Cell and Developmental Biology, Division of Biology, University of
California, San Diego, La Jolla, California 92093 (U.S.A.)
Eukaryotic Cell, in press
We recently isolated a DNA-binding protein from Dictyostelium discoideum
cells, CbfA, that interacts in vitro with a regulatory element in
retrotransposon TRE5-A. We have generated a mutant strain that expresses CbfA
at <5% of wild-type level to characterize the consequences on D. discoideum
cell physiology. We found that the multicellular development program leading
to fruiting body formation is highly compromised in the mutant. The cells
cannot aggregate and stay as a monolayer almost indefinitely. The cells
respond properly to prestarvation conditions by expressing discoidin in a
cell density-dependent manner. A genome-wide microarray-assisted expression
analysis combined with Northern blot analyses revealed a failure of
CbfA-depleted cells to induce the aggregation-specific adenylyl cyclase ACA
and other genes required for cAMP signal relay that is necessary for
aggregation and subsequent multicellular development. However, the cbfA
mutant aggregated efficiently when mixed with as few as 5% wild-type cells.
Moreover, pulsing cbfA mutant cells developing in suspension with nanomolar
levels of cAMP resulted in induction of acaA and other early developmental
genes. Although the response was less efficient and slower than in wild-type
cells, it showed that cells depleted in CbfA are able to initiate development
if given exogenous cAMP signals. Ectopic expression of the gene encoding the
catalytic subunit of protein kinase A restored multicellular development of
the mutant. We conclude that sensing of cell density and starvation are
independent of CbfA, whereas CbfA is essential for the pattern of gene
expression which establishes the genetic network leading to aggregation and
multicellular development of D. discoideum.
Submitted by: Thomas Winckler <winckler@em.uni-frankfurt.de
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[End Dicty News, volume 22, number 17]
