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dictyNews Volume 22 Number 08
Dicty News
Electronic Edition
Volume 22, number 8
April 2, 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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A homologue of Cdk8 is required for spore cell differentiation in
Dictyostelium
Hsiu-Hsu Sophia Lin, Meenal Khosla, Hao-Jen Huang, Duen-Wei Hsu,
Christine Michaelis, Gerald Weeks and Catherine Pears
Dev Biol., in press
The Cdk8 proteins are kinases which phosphorylate the carboxy terminal
domain (CTD) of RNA polymerase II as well as some transcription factors and,
therefore, are involved in the regulation of transcription. Here we report
that a Cdk8 homologue from Dictyostelium discoideum is localised in the
nucleus where it forms part of a high molecular weight complex that has CTD
kinase activity. Insertional mutagenesis was used to abrogate gene function
and analysis of the null strain revealed that the DdCdk8 protein plays an
important role in spore formation during late development. As previously
reported (Takeda, K., Saito, T. and Ochiai, H. 2002. Develop. Growth Differ.
44, 213-223) Ddcdk8- cells also exhibit impaired aggregation, although we
report that the severity of the defect depends upon experimental conditions.
When aggregation occurs, Ddcdk8- cells form abnormal terminally
differentiated structures within which the Ddcdk8- cells differentiate into
stalk cells but fail to form spores, indicating a role for DdCdk8 in cell
differentiation. When Ddcdk8 is expressed from its own promoter the protein
is able to rescue both the late developmental defect and the impaired
aggregation. However, when expressed from an heterologous promoter only
the impaired aggregation is rescued. This result demonstrates that the
defect during late development is not a consequence of impaired aggregation
and indicates a direct role for DdCdk8 in spore formation.
Submitted by: Catherine Pears [catherine.pears@bioch.ox.ac.uk]
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Chemoattractant induced Ras activation during Dictyostelium aggregation
Helmut Kae, Chinten James Lim, George B. Spiegelman, Gerald Weeks
Department of Microbiology and Immunology
University of British Columbia,
300-6174 University Boulevard,
Vancouver, British Columbia, Canada
V6T 1Z3
EMBO Reports, in press
Ras proteins are highly conserved molecular switches that regulate cellular
response to external stimuli. Dictyostelium discoideum contains an extensive
family of Ras proteins that function in regulation of mitosis, cytoskeletal
function and motility, and the onset of development. Little is known about
the events that lead to the activation of Ras proteins in Dictyostelium,
primarily due to a lack of a biochemical assay to measure levels of activated
Ras. We have adapted an assay used successfully to measure activated Ras in
mammalian cells to monitor activation of two Dictyostelium Ras proteins,
RasC and RasG. We have found that the Ras Binding Domain (RBD) of mammalian
Raf1 was capable of binding to the activated form of RasG, but not to the
activated form of RasC; however, the RBD of Schizosaccharomyces pombe Byr2
was capable of binding preferentially to the activated forms of both RasC
and RasG. Using this assay, we discovered that RasC and RasG showed a rapid
and transient activation when aggregation competent cells were stimulated
with the chemoattractant cAMP, and this activation did not occur in a number
of cAMP signalling mutants. This data provides further evidence of a role
for both RasC and RasG in the early development of Dictyostelium.
Submitted by: Helmut Kae [hkae@interchange.ubc.ca]
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Ecological succession of dictyostelid slime molds on the island of Hawaii
Andrew R. Swanson(1), John D. Shadwick(1), Don E. Hemmes(2) and
Frederick W. Spiegel(1)
(1)Department of Biological Sciences, University of Arkansas, Fayetteville,
Arkansas, 72701, USA
(2)Department of Biology, University of Hawaii, Hilo, Hawaii, 96720, USA
Systematics and Geography of Plants, in press
Patterns of ecological succession have been demonstrated for decomposer
communities, but the details of such patterns with respect to the role of
eumycetozoans have not been addressed. Successional patterns can be inferred
from a sequence of closely located sites which differ only in age, but are
controlled for other sources of variation. Hawaii, the largest and youngest
of the Hawaiian Islands, offers an ideal site for such studies, consisting of
variously-aged landforms underlain by similar substrates, and influenced by
similar climates and biotic communities. Soil/litter samples were collected
from nine montane mesic sites of similar elevation and rainfall, but ranging
in substrate age from 67 to 10,000 ybp. Samples were processed to recover
dictyostelid (cellular) slime molds according to established protocols.
Results suggest that slightly different assemblages of dictyostelids occupy
the soil/litter derived from different-aged parent materials. The density and
species diversity of dictyostelids was higher in soil/litter samples from the
youngest sites. The time necessary for dictyostelids to colonize a site is
less than 67 years. It is hypothesized that colonization of the soil/litter
by dictyostelids is followed by the arrival of predators, particularly
nematodes, which adversely affect the density and species diversity of soil
amoebae in general, and dictyostelids in particular.
Submitted by: Andrew R. Swanson [arswans@uark.edu]
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[End Dicty News, volume 22, number 8]
