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dictyNews Volume 21 Number 04
Dicty News
Electronic Edition
Volume 21, number 4
August 15, 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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Cross-linking of actin filaments by myosin II is a major contributor to
cortical integrity and cell motility in restrictive environments
Gary Laevsky and David A. Knecht
Journal of Cell Science, in press
Cells are frequently required to move in a local environment that physically
restricts locomotion, such as during extravasation or metastatic invasion.
In order to model these events, we have developed an assay in which
vegetative Dictyostelium amoebae undergo chemotaxis under a layer of agarose
toward a source of folic acid [Laevsky, G. and Knecht, D. A. (2001).
Biotechniques 31, 1140-1149]. As the concentration of agarose is increased
from 0.5% to 3% the cells are increasingly inhibited in their ability to
move under the agarose. The contribution of myosin II and actin
cross-linking proteins to the movement of cells in this restrictive
environment has now been examined. Cells lacking myosin II heavy chain
(mhcA-) are unable to migrate under agarose overlays of greater than 0.5%,
and even at this concentration they move only a short distance from the
trough. While attempting to move, the cells become stretched and fragmented
due to their inability to retract their uropods. At higher agarose
concentrations, the mhcA- cells protrude pseudopods under the agarose, but
are unable to pull the cell body underneath. Consistent with a role for
myosin II in general cortical stability, GFP-myosin dynamically localizes
to the lateral and posterior cortex of cells moving under agarose. Cells
lacking the essential light chain of myosin II (mlcE-), have no measurable
myosin II motor activity, yet were able to move normally under all agarose
concentrations. Mutants lacking either ABP-120 or a-actinin were also able
to move under agarose at rates similar to wild-type cells. We hypothesize
that myosin stabilizes the actin cortex through its cross-linking activity
rather than its motor function and this activity is necessary and
sufficient for the maintenance of cortical integrity of cells undergoing
movement in a restrictive environment. The actin cross-linkers a-actinin
and ABP-120 do not appear to play as major a role as myosin II in providing
this cortical integrity.
Submitted by: David Knecht [knecht@uconnvm.uconn.edu]
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Cell movements and traction forces during the migration of 2-dimensional
Dictyostelium slugs.
Jean-Paul Rieu1, Kaoru Tsuchiya2, Satoshi Sawai2, Yasuo Maeda3, and Yasuji
Sawada4
1Laboratorie de Physique de la Matiere Condensee et des Nanostructures,
Universite Claude Bernard Lyon I, 43 Boulevard du 11 Novembre 1918, 69622
Villeurbanne Cedex, France; 2Graduate School of Information Science, Tohoku
University, 2-1-1 Katahira, Sendai 980-9577, Japan; 3Department of
Developmental Biology and Neurosciences, Graduate School of Life Sciences,
Tohoku University, Aoba, Sendai 980-8578, Japan; 4Tohoku Institute of
Technology, 35-1 Yagiyama-Kasumi, Taihaku, 983, Japan
Journal of Biological Physics, in press
Abstract:
Migration of Dictyostelium discoideum slugs results from complex
coordinated movements and traction forces of its constituent cells. In this
work, we show that two-dimensional (2D) slugs are good models for slug
motility studies. They share most of the properties of 3D slugs but are more
suitable for microscopy. We performed observations of substrate deformations
during 2D slug migration. Traction forces on elastic substrates exerted by
the cells are maximal in the central prespore region and absent in the
anterior prestalk region.
Submitted by: Yasuo MAEDA [ymaeda@mail.cc.tohoku.ac.jp]
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[End Dicty News, volume 21, number 4]
