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dictyNews Volume 18 Number 04
Dicty News
Electronic Edition
Volume 18, number 4
March 2, 2002
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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Correlates of developmental cell death in Dictyostelium discoideum
Trupti Kawli, B.R. Venkatesh, P. Kevin Kennady*, Gopal Pande* and Vidyanand
Nanjundiah
Indian Institute of Science, Bangalore 560012, India and *Centre for Cellular
and Molecular Biology, Hyderabad 500007
Differentiation, in press
ABSTRACT
We have studied the correlates of cell death during normal development in
Dictyostelium discoideum. Our main findings are four. (i) There is a
gradual increase in the number of cells with exposed phosphatidyl serine
residues, an indicator of membrane asymmetry loss and increased permeability.
Only presumptive stalk cells show this change in membrane asymmetry. Also,
under conditions that promote calcium-induced stalk cell differentiation in
cell monolayers, cells show an increase in cell membrane permeability. (ii)
There is a gradual fall in mitochondrial membrane potential during
development, again restricted to the presumptive stalk cells. (iii) The
fraction of cells showing caspase-3 activity increases as development
proceeds and then declines in the terminally differentiated fruiting body.
(iv) There is an absence of internucleosomal cleavage of DNA, or DNA
fragmentation. There is also no calcium and magnesium-dependent
endonucleolytic activity seen in nuclear extracts from various developmental
stages. However, nuclear condensation and peripheralization does occur in
stalk cells. Thus, cell death in D.discoideum shows some, but not all,
features of apoptosis as recognized in other multicellular systems. These
findings argue against the emergence of a single mechanism of 'programmed
cell death (PCD)' before multicellularity arose during evolution.
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Lamellipodial localization of Dictyostelium myosin heavy chain kinase A is
mediated via F-actin binding by the coiled-coil domain
Paul A. Steimle(a), Lucila Licate(b), Graham P. Ct(c), and Thomas T.
Egelhoff(b)
(a)Department of Biology University of North Carolina at Greensboro,
Greensboro, NC 27402; (b)Department of Physiology and Biophysics Case Western
Reserve School of Medicine Cleveland, OH 44106; (c) Department of
Biochemistry, Queen s University Kingston, Ontario, CANADA
FEBS Letters, In Press
ABSTRACT
Myosin heavy chain kinase A (MHCK A) modulates myosin II filament assembly in
the amoeba Dictyostelium discoideum. MHCK A localization in vivo is
dynamically regulated during chemotaxis, phagocytosis, and other polarized
cell motility events, with preferential recruitment into anterior F-actin
rich structures. The current work reveals that an amino-terminal segment of
MHCK A, previously identified as forming a coiled-coil, mediates anterior
localization. MHCK A co-sediments with F-actin, and deletion of the amino-
terminal domain eliminated actin binding. These results indicate that the
anterior localization of MHCK A is mediated via direct binding to F-actin,
and reveal the presence of an actin-binding function not previously detected
by primary sequence evaluation of the coiled-coil domain.
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Genetic and morphological evidence for two parallel pathways of cell cycle-
coupled cytokinesis in Dictyostelium.
Akira Nagasaki1, Eugenio L. de Hostos2 and Taro Q.P. Uyeda1
1: Gene Discovery Research Center, National Institute of Advanced Industrial
Science and Technology, Tsukuba, Ibaraki 305-8562, Japan; 2: Department of
Cell Genetics, Exelixis Inc., South San Francisco, CA 94083-0511, USA
J. Cell. Sci., in press.
SUMMARY
Myosin II-null cells of Dictyostelium discoideum cannot divide in
suspension, consistent with the dogma that myosin II drives constriction
of the cleavage furrow, and consequently, cytokinesis (cytokinesis A).
Nonetheless, when grown on substrates, these cells exhibit efficient, cell
cycle-coupled division, suggesting that they possess a novel, myosin II-
independent, adhesion-dependent method of cytokinesis (cytokinesis B).
Here we show that double mutants lacking myosin II and either AmiA or
coronin, both of which are implicated in cytokinesis B, are incapable of
cell cycle-coupled cytokinesis. These double mutants multiplied in number
mainly by cytokinesis C, a third, inefficient method of cell division, which
requires substrate adhesion and is independent on the cell cycle progression.
In contrast, double mutants lacking AmiA and coronin were not sicker than
each of the single mutant, indicating that the severe defects of myosin II-/
AmiA- or myosin II-/coronin- are not simple additive effects of two mutations.
We take this as genetic evidence for two parallel pathways that both lead to
cell cycle-coupled cytokinesis. This conclusion is supported by differences
in morphological changes during cytokinesis of the mutant cell lines.
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Mini review: Gene expression patterns in Dictyostelium using microarrays
Gad Shaulsky and William F. Loomis
Department of Molecular and Human Genetics, Baylor College of Medicine,
Houston, TX 77030. Division of Biology, University of California, San Diego,
La Jolla, CA 92093.
Protist (in press)
(no abstract)
The promises and perils of microarray analyses of gene expression are
considered and the results from recent microarray studies in Dictyostelium
compared and summarized. The avenues open for future microarray studies are
briefly discussed.
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[End Dicty News, volume 18, number 4]
