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dictyNews Volume 26 Number 11
dictyNews
Electronic Edition
Volume 26, number 11
April 14, 2006
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 dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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GABA induces terminal differentiation of Dictyostelium through a GABAB type
receptor
Christophe Anjard and William F. Loomis
Center for Molecular Genetics, Division of Biological Sciences,
University of California San Diego, La Jolla, CA 92093-0368
Development, in press
When prespore cells approach the top of the stalk in a Dictyostelium
fruiting body, they rapidly encapsulate in response to the signalling
peptide, SDF-2. Glutamate decarboxylase, the product of the gadA gene,
generates GABA from glutamate. gadA is expressed exclusively in prespore
cells late in development. We found that GABA induces the release of the
precursor of SDF-2, AcbA, from prespore cells. GABA also induces exposure of
the protease domain of TagC on the surface of prestalk cells where it can
convert AcbA to SDF-2. The receptor for GABA in Dictyostelium, GrlE, is a
seven-transmembrane G-protein coupled receptor that is most similar to
GABA-B type receptors. The signal transduction pathway from GABA/ GrlE
appears to be mediated by PI3 kinase and the PKB related protein kinase
PkbR1. Glutamate acts as a competitive inhibitor of GABA functions in
Dictyostelium and is also able to inhibit induction of sporulation by
SDF-2. The signal transduction pathway from SDF-2 is independent of the
GABA/ glutamate signal transduction pathway but the two appear to converge
to control release of AcbA and exposure of TagC protease. These results
indicate that GABA is not only a neurotransmitter but also an ancient
intercellular signal.
Submitted by: Bill Loomis [wloomis@ucsd.edu]
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Filopodia Formation in the Absence of Functional WAVE and Arp2/3 Complexes
Anika Steffen 1, Jan Faix 2, Guenter P. Resch 3, Joern Linkner 2,
Juergen Wehland 1, J. Victor Small 3, Klemens Rottner 1, and
Theresia E.B. Stradal 1
1) Signalling and Motility Group, Cytoskeleton Dynamics Group, and
Department of Cell Biology, German Research Centre for Biotechnology,
D-38124 Braunschweig, Germany; 2)Institute of Biophysical Chemistry,
Hannover Medical School, D-30623 Hannover, Germany; 3) Institute of
Molecular Biotechnology, Austrian Academy of Sciences, A-1030 Vienna,
Austria
Mol. Biol. Cell, in press.
Cell migration is initiated by plasma membrane protrusions, in the form of
lamellipodia and filopodia. The latter rod-like projections may exert
sensory functions and are found in organisms as distant in evolution as
mammals and amoeba like Dictyostelium discoideum. In mammals, lamellipodia
protrusion downstream of the small GTPase Rac1 requires a multimeric
protein assembly, the WAVE-complex, which activates Arp2/3-mediated actin
filament nucleation and actin network assembly. A current model of
filopodia formation postulates that these structures arise from a dendritic
network of lamellipodial actin filaments by selective elongation and
bundling. Here we have analyzed filopodia formation in mammalian cells
abrogated in expression of essential components of the lamellipodial actin
polymerization machinery. Cells depleted of the WAVE-complex component
Nap1 and, in consequence, of lamellipodia, exhibited normal filopodia
protrusion. Likewise, the Arp2/3-complex, which is essential for
lamellipodia protrusion, is dispensable for filopodia formation. Moreover,
genetic disruption of nap1 or the WAVE-orthologue scar (suppressor of cAMP
receptor) in Dictyostelium was also ineffective in preventing filopodia
protrusion. These data suggest that the molecular mechanism of filopodia
formation is conserved throughout evolution from Dictyostelium to mammals
and show that lamellipodia and filopodia formation are functionally
separable.
Submitted by: Hans Faix [faix@bpc.mh-hannover.de]
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Transcriptional regulation of Dictyostelium pattern formation
Jeffrey G. Williams
School of Life Sciences
University of Dundee
Dow Street
Dundee DD1 5EH
UK
j.g.williams@dundee.ac.uk
EMBO reports, in press
On starvation, Dictyostelium cells form a terminally differentiated
structure, the fruiting body, which comprises stalk cells and spore cells.
Their precursorsÑprestalk and prespore cellsÑare spatially separated and
accessible in a migratory structure known as the slug. This simplicity and
manipulability has made Dictyostelium attractive to both experimental and
theoretical developmental biologists. However, this outward simplicity
conceals a surprising degree of developmental sophistication. Multiple
prestalk sub-types are formed and they undertake a co-ordinated series of
morphogenetic cell movements to generate the fruiting body. This review
describes recent advances in understanding the signalling pathways that
generate prestalk cell heterogeneity, focusing on the roles of the prestalk
cell inducer differentiation-inducing factor-1 (DIF-1), the tip inducer
cAMP and the transcription factors that mediate their action. These include
signal transducers and activators of transcription (STAT) proteins, basic
leucine zipper (bZIP) proteins and a Myb protein of a class previously only
described in plants.
Submitted by: jeff Williams [j.g.williams@dundee.ac.uk]
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The Dictyostelium genome
William F. Loomis
Cell and Developmental Biology, Division of Biology,
University of California San Diego, La Jolla, CA 92093
Curr. Issues in Mol. Biol., in press
The 34 Mb genome of Dictyostelium discoideum is carried on 6 chromosomes
and has been fully sequenced by an international consortium. The sequence
was assembled on the classical and physical maps that had been built up over
the years and refined by HAPPY mapping. Annotation of the sequence
predicted about 12,000 genes for proteins of at least 50 amino acids in
length. The total number of amino acids encoded (the proteome) is more than
double that in yeast and rivals that of metazoans. The genome sequence
shows all the proteins available to Dictyostelium as well as definitively
showing which domains have been lost since Dictyostelium diverged from the
line leading to metazoans. Genomics opens the door to determining the
expression patterns of all the genes during growth and development using
microarrays. This approach has already uncovered a wealth of new markers
for the stages of development and the various cell types. Transcription
factors and their cis-regulatory sites that account for the surprising
complexity of Dictyostelium development can be analyzed much more easily
now that we have the complete sequence.
Submitted by: Bill Loomis [wloomis@ucsd.edu]
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[End dictyNews, volume 26, number 11] 
