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dictyNews Volume 17 Number 04
Dicty News
Electronic Edition
Volume 17, number 4
Sept. 1, 2001
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu.
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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Cofilin-2, a novel type of cofilin, is expressed specifically at
aggregation stage of Dictyostelium discoideum development.
Hiroyuki Aizawa1*, Yoshiro Kishi2, Kazuko Iida1, Masazumi
Sameshima2, and Ichiro Yahara1.
1Department of Cell Biology, 2Electron Microscopy Center,
The Tokyo Metropolitan Institute of Medical Science,
Honkomagome 3-18-22, Bunkyo-ku, Tokyo 113-8613, Japan.
*Present address: Department of Neuroscience, Johns Hopkins
University School of Medicine, 725 North Wolfe Street, PCTB
1004, Baltimore, MD 21205, USA
Genes to Cells in press.
Abstract
Background: A conventional cofilin, cofilin-1 in Dictyostelium discoideum
plays significant roles in cell proliferation, phagocytosis, chemotactic
movement and macropinocytosis.
Results: We identified a new member of the cofilin family, named cofilin
-2 in D. discoideum. Cofilin-2 shows significant homology to a conventional
Dictyostelium cofilin, cofilin-1, through its entire sequence, and contains
residues conserved among the cofilin family that are responsible for actin-
binding. On the other hand, several residues that are conserved among the
cofilin family are missing from cofilin-2. Purified cofilin-2 depolymerized
actin filaments in a dose- and pH-dependent manner and reduced the apparent
viscosity of an actin solution, although they did not co-sediment with actin
filaments at all. Cofilin-2 was not expressed in vegetative cells, but was
transiently induced during the aggregation stage of development, whereas
cofilin-1 was predominantly expressed in vegetative cells. Immunocytochemistry
revealed that cofilin-2 localizes at substrate adhesion sites, where cofilin-1
is almost completely excluded. Disruption of the cofilin-2 gene caused an
increase in actin accumulation at the substrate adhesion sites. We also found
that cofilin-2 did not rescue cof1 gene null yeast cells, whereas cofilin-1
did.
Conclusions: Cofilin-2 may play a distinct role from that of cofilin-1 in
destabilization of the actin cytoskeleton during Dictyostelium development.
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Propagating chemo-attractant waves co-ordinate periodic cell movement
in Dictyostelium slugs
Dirk Dormann & Cornelis J. Weijer
School of Life Sciences, Division of Cell and Developmental Biology, Wellcome
Trust Biocentre, University of Dundee, Dundee DD1 5EH, UK
ABSTRACT
Migration and behaviour of Dictyostelium slugs results from co-ordinated
movement of its constituent cells. It has been proposed that cell movement
is controlled by propagating waves of cAMP as during aggregation and in the
mound. We report here the existence of optical density waves in slugs, they
are initiated in the tip and propagate backwards. The waves reflect periodic
cell movement and are mediated by cAMP since injection of cAMP or cAMP
phosphodiesterase disrupts wave propagation and results in effects on cell
movement and therefore slug migration. Inhibiting the function of the cAMP
receptor cAR1 blocks wave propagation, showing that the signal is mediated by
cAR1. Wave initiation is strictly dependent on the tip, in decapitated slugs
no new waves are initiated and slug movement stops until a new tip regenerates.
Isolated tips continue to migrate while producing waves. We conclude from
these observations that the tip acts as a pacemaker for cAMP waves that
coordinate cell movement in slugs.
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Extracting transcriptional events from temporal gene expression patterns
during Dictyostelium development.
R. Sasik, N. Iranfar*, T. Hwa, and W.F. Loomis*
Department of Physics and *Division of Biology
University of California San Diego, La Jolla, CA 92093
Bioinformatics, in press
DNA microarray technology can generate a large amount of data describing
time-course of gene expression. These data, when properly interpreted, can
yield a great deal of information concerning differential gene expression
during development. Much current effort in bioinformatics has been devoted
to the analysis of gene expression data, usually via some "clustering
analysis" on the raw data in some abstract high dimensional space. Here, we
describe a method where we first "process" the raw time-course data using a
simple biologically based kinetic model of gene expression profile e.g.,
the times of the onset and cessation of the expression of the
developmentally regulated genes. These vital attributes can then be
trivally clustered by visual inspection to reveal biologically significant
effects. We have applied this approach to microarray expression data from samples
isloated every two hours throughout the 24-hour developmental program of
Dictyostelium discoideum. mRNA accumulation patterns for 50 developmental
genes were found to fit the kinetic model with a p-value of 0.05 or better.
Transcription of these genes appears to be initiated in bursts at
well-defined periods during development, in a manner suggestive of a
dependent sequence. This approach can be applied to analyses of other
temporal expression patterns, including those of the cell cycle.
Intensity ratios for all genes in this study are available at
http://www.biology.ucsd.edu/loomis-cgi/microarray/ index.html
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[End Dicty News, volume 17, number 4]
