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dictyNews Volume 20 Number 09
Dicty News
Electronic Edition
Volume 20, number 9
May 23, 2003
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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Formation of Hirano Bodies Induced by Expression of
an Actin Cross-linking Protein With a Gain of Function Mutation
Andrew Maselli, Ruth Furukawa, Susanne A. M. Thomson,
Richard C. Davis, and Marcus Fechheimer
Department of Cellular Biology, University of Georgia, Athens, Georgia 30602
Eucaryotic Cell, in press
Hirano bodies are paracrystalline actin filament containing structures
reported in association with a variety of neurodegenerative diseases. Yet,
the biological function of Hirano bodies remains poorly understood, since
nearly all prior studies of these structures employed post-mortem samples
of tissue. In the present study, we have generated a full length form of a
Dictyostelium 34 kDa actin cross-linking protein with point mutations in
the first putative EF hand termed 34 kDa _EF1. The 34 kDa _EF1 protein
binds calcium normally, but has activated actin binding that is unregulated
by calcium. Expression of the 34 kDa _EF1 protein in Dictyostelium induced
the formation of Hirano bodies as assessed both by fluorescence microscopy
and transmission electron microscopy. Dictyostelium cells bearing Hirano
bodies grow normally, indicating that Hirano bodies are not associated with
cell death and are not deleterious to cell growth. Moreover, expression of
the 34 kDa ÆEF1 protein rescues the phenotypes of 34 kDa null and 34
kDa/_-actinin double null cells. Finally, expression of the 34 kDa _EF1
protein also initiates formation of Hirano bodies in cultured mouse
fibroblasts. These results show that failure to regulate the activity
and/or affinity of an actin cross-linking protein can provide a signal for
formation of Hirano bodies. More generally, formation of Hirano bodies is
a cellular response to or a consequence of aberrant function of the actin
cytoskeleton.
Submitted by: Andrew Maselli [amaselli@uconnvm.uconn.edu]
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Shared, Unique and Redundant Functions of Three Myosin Is (MyoA, MyoB and
MyoF) in Motility and Chemotaxis in Dictyostelium
David L. Falk*, Deborah Wessels*, Leslie Jenkins*, Tien Pham1,
Spencer Kuhl*, Margaret A. Titus^ and David R. Soll*
*WM Keck Dynamic Image Analysis Facility, Dept. Biological Sciences,
University of Iowa, Iowa City, IA 52242,
^Dept. Genetics, Cell Biology and Development, University of Minnesota,
Minneapolis, MN
J. Cell Science, in press
Most cell types express two distinct forms of myosin I, amoeboid and short,
distinguished by differences in their tail domains. Both types of myosin I
have been implicated in the regulation of pseudopod formation in
Dictyostelium discoideum. Computer-assisted methods for reconstructing and
motion analyzing cells, and experimental protocols for assessing the basic
motile behavior of mutant cells in buffer and the responses of these cells
to the individual spatial, temporal and concentration components of a
natural wave of the chemoattractant cAMP were used to assess shared, unique
or redundant roles of three class I myosins, one amoeboid, myoB, and two
short, myoA and myoF, in motility. Analysis of both single and double
mutants revealed that all three myosins play independent roles in
suppressing lateral pseudopod formation in buffer and during chemotaxis.
One, myoB, also plays a unique role in priming cells to respond to the
increasing temporal gradient in the front of cAMP waves, while myoF plays a
unique role in maintaining the elongate, polarized shape of a cell in buffer,
during chemotaxis in a spatial gradient of chemoattractant and in the front
of a cAMP wave. Finally, myoA and myoF play redundant roles in the velocity
response to the increasing temporal gradient in the front of a cAMP wave.
These results, therefore, reveal an unexpected variety of shared, unique and
redundant functions of the three myosin Is in motility and chemotaxis.
Interestingly, the combined defects of the myosin I mutants are similar to
those of a single mutant with constitutive PKA activity, suggesting that PKA
plays a role in the regulation of all three myosin Is.
Submitted by: Deborah Wessels [deborah-wessels@uiowa.edu]
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Human Polymorphonuclear Leukocytes Respond To Waves Of Chemoattractant Like
Dictyostelium
Jeremy Geiger, Deborah Wessels and David R. Soll
W. M. Keck Dynamic Image Analysis Facility, Department of Biological Sciences,
The University of Iowa, Iowa City, IA 52242
Cell Motility and the Cytoskeleton, in press
It has been assumed that the natural chemotactic signal that attracts human
polymorphonuclear leukocytes (PMNs) over long distances to sites of infection
is in the form of a standing spatial gradient of chemoattractant. We have
questioned this assumption on the grounds first that standing spatial
gradients may not be stable over long distances for long periods of time and
second that in the one animal cell chemotaxis system in which the natural
chemotactic signal has been described in space and time, aggregation of
Dicytostelium discoideum, the signal is in the form of an outwardly relayed,
nondissipating wave of attractant. Here, it is demonstrated that PMNs alter
their behavior in each of the four phases of a wave of PMN chemoattractant,
fashioned after the Dictyostelium wave, in a manner similar to Dictyostelium.
These results demonstrate that PMNs have all of the machinery to respond to
a natural wave of attractant, providing support to the hypothesis that the
natural signal that attracts PMNs over large distances to sites of infection
in the human body may also be in the form of a wave.
Submitted by: Deborah Wessels [deborah-wessels@uiowa.edu]
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[End Dicty News, volume 20, number 9]
