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dictyNews Volume 24 Number 04
Dicty News
Electronic Edition
Volume 24, number 4
February 25, 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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Microbial Development
Fisher, P.R.
Encyclopedia of Molecular Cell Biology and Medicine, in press.
Development is not only restricted to large multicellular animals and plants
but is also a feature of the life cycles of microorganisms. The environment
of a microorganism is rapidly changeable so that both eukaryotic and
prokaryotic microbes have evolved developmental strategies to enhance their
nutrient-scavenging abilities or in more extreme circumstances to form
dormant, resistant cells (spores). The spores can survive under harsh
conditions that do not support growth and can be dispersed to other
environments that do. The endospores of pathogenic Clostridium species are
amongst the most resistant cells on earth, and their destruction (or removal)
is the key criterion for successful microbiological sterilization.
Developmental programs in microbial pathogens are initiated in response to
infection of the host and play important roles in pathogenesis. However, the
best-understood examples of microbial development are not pathogens, but
free-living microbes. The general principles underlying microbial
development are being elucidated by their study.
Submitted by: Paul R. Fisher [P.Fisher@latrobe.edu.au]
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Identification and characterization of a novel alpha kinase with a vWFA
motif localized to the contractile vacuole and Golgi complex in
Dictyostelium discoideum
Venkaiah Betapudi, Cynthia Mason, Lucila Licate and Thomas T. Egelhoff
Department of Physiology and Biophysics, Case Western Reserve University,
10900 Euclid Avenue, Cleveland, OH 44106-4970, USA.
Mol. Biol. Cell in Press
We have identified a novel unconventional protein kinase in Dictyostelium
discoideum which carries the same conserved class of "alpha kinase"
catalytic domain as previously reported in myosin heavy chain kinases
(MHCKs) in this amoeba, but which has a completely novel domain
organization. This protein of 625 amino acids contains an N-terminal von
Willebrand Factor A (vWFA) motif (also known as beta-integrin motif), and
is therefore named as VwkA. Manipulation of VwkA expression level via high
copy number plasmids (VwkA++ cells) or gene disruption (vwkA null cells)
results in an array of cellular defects, including impaired growth and
multinucleation in suspension culture, impaired development, and alterations
in myosin II abundance and assembly level. Despite sequence similarity to
MHCKs, the purified protein failed to phosphorylate myosin II in vitro.
Autophosphorylation activity however, was enhanced by calcium/calmodulin,
and the enzyme can be precipitated from cellular lysates with
calmodulin-agarose, suggesting that VwkA may directly bind calmodulin. VwkA
is cytosolic in distribution, but enriched on the membranes of the
contractile vacuole and Golgi-like structures in the cell. We propose that
VwkA likely acts indirectly to influence myosin II abundance and assembly
behavior, and possibly has broader roles the previously characterized alpha
kinases in this organism which all appear to be MHC
kinases.
Submitted by: Dr. Tom Egelhoff [tte@po.cwru.edu]
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GOAT: an R tool for analyzing Gene Ontology term enrichment
Qikai Xu and Gad Shaulsky
Graduate Program in Structural and Computational Biology and Molecular
Biophysics, Department of Molecular and Human Genetics, Baylor College
of Medicine, Houston, TX
Applied Bioinformatics, in press
Summary: Understanding the composition of gene lists that result from high
throughput experiments requires elaborate processing of gene annotation
lists. Here we present GOAT, a tool based on the statistical software "R"
for analyzing Gene Ontology (GO) term enrichment in gene lists. Given a
gene list, GOAT calculates the enrichment and statistical significance of
every GO term and generates graphical presentations of significantly
enriched terms. GOAT works for any organism with a genome-scale GO
annotation and allows easy updates of ontologies and annotations.
Availability: GOAT is freely available (see supplement).
Supplementary information: http://dictygenome.org/software/GOAT/
Key words: Gene Ontology (GO), GOAT, Microarray, R
Submitted by: Gadi Shaulsky [gadi@bcm.tmc.edu]
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A Dictyostelium homologue of WASP is required for polarized F-actin assembly
during chemotaxis.
Scott A. Myers, Ji W. Han, Yoonsung Lee, Richard A. Firtel, and
Chang Y. Chung.
Molecular Biology of the Cell
The actin cytoskeleton controls the overall structure of cells and is
highly polarized in chemotaxing cells, with F-actin assembled predominantly
in the anterior leading edge and to a lesser degree in the cell's posterior.
Wiscott-Aldrich syndrome protein (WASP) has emerged as a central player in
controlling actin polymerization. We have investigated WASP function and its
regulation in chemotaxing Dictyostelium cells and demonstrated the specific
and essential role of WASP in organizing polarized F-actin assembly in
chemotaxing cells. Cells expressing very low levels of WASP show reduced
F-actin levels and significant defects in polarized F-actin assembly,
resulting in an inability to establish axial polarity during chemotaxis.
GFP-WASP preferentially localizes at the leading edge and uropod of
chemotaxing cells and the B domain of WASP is required for the localization
of WASP. We demonstrated that the B domain binds to PI(4,5)P2 and PI(3,4,5)P3
with similar affinities. The interaction between the B domain and PI(3,4,5)P3
plays an important role for the localization of WASP to the leading edge in
chemotaxing cells. Our results suggest that the spatial and temporal control
of WASP localization and activation is essential for the regulation of
directional motility.
Submitted by: Chang Chung [chang.chung@vanderbilt.edu]
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[End Dicty News, volume 24, number 4] 
