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dictyNews Volume 25 Number 02
Dicty News
Electronic Edition
Volume 25, number 2
July 29, 2005
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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TOR Complex 2 Integrates Cell Movement during Chemotaxis and Signal Relay
in Dictyostelium
Susan Lee1, Frank I. Comer, Atsuo Sasaki, Ian X. McLeod, Yung Duong,
Koichi Okumura, John R. Yates III, Carole A. Parent, and Richard A. Firtel
Mol. Cell. Bio. in press
Dictyostelium cells form a multicellular organism through the
aggregation of independent cells. This process requires both chemotaxis
and signal relay in which the chemoattractant cAMP activates adenylyl
cyclase through the G protein-coupled cAMP receptor cAR1. cAMP is produced
and secreted and it activates receptors on neighboring cells, thereby
relaying the chemoattractant signal to distant cells. Using
co-immunoprecipitation and mass spectrometric analyses, we have identified
a TOR-containing complex in Dictyostelium that is related to the TORC2
complex of S. cerevisiae and regulates both chemotaxis and signal relay.
We demonstrate that mutations in Dictyostelium LST8, RIP3, and Pia,
orthologs of the yeast TORC2 components LST8, AVO1, and AVO3, exhibit a
common set of phenotypes including reduced cell polarity, chemotaxis speed
and directionality, phosphorylation of Akt/PKB and the related PKBR1, and
activation of adenylyl cyclase. Further, we provide evidence for a role
of Ras in the regulation of TORC2. We propose that, through the regulation
of chemotaxis and signal relay, TORC2 plays an essential role in
controlling aggregation by coordinating the two essential arms of the
developmental pathway that leads to multicellularity in Dictyostelium.
Submitted by: Rick Firtel [rafirtel@ucsd.edu]
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Direct mechanical force measurements during the migration of Dictyostelium
slugs using flexible substrata
Jean-Paul Rieu 1*, Catherine Barentin 1, Yasuo Maeda 2 and Yasuji Sawada 3
1 Laboratoire de Physique de la Matiere Condensee et
Nanostructures,Universite Claude Bernard Lyon I & CNRS, 43 Boulevard du 11
Novembre, 69622 Villeurbanne Cedex, France; 2 Department of Developmental
Biology and Neurosciences, Graduate School of Life Sciences, Tohoku
University, Aoba, Sendai 980-8578, Japan; 3 Tohoku Institute of Technology,
35-1 Yagiyama-Kasumi, Taihaku, 983, Sendai, Japan.
Biophysical Journal, in press
We use the flexible substrate method to study how and where are exerted
mechanical forces during the migration of Dictyostelium slugs. This old and
contentious issue has been left poorly understood so far. We are able to
identify clearly separate friction forces in the tip and in the tail of the
slug, traction forces mostly localized in the inner slug/surface contact
area in the prespore region and large perpendicular forces directed in the
outward direction at the outline of contact area. Surprisingly, the
magnitude of friction and traction forces is decreasing with slug velocity
indicating that these quantities are probably related to the dynamics of
cell/substrate adhesion complexes. Contrary to what is always assumed in
models and simulations, friction is not of fluid type (viscous drag) but
rather close to solid friction. We suggest that the slime sheath confining
laterally the cell mass of the slug experiences a tension that in turn is
pulling out the elastic substrate in the direction tangential to the slug
profile where sheath is anchored. In addition, we show in the appendix that
the iterative method we developed is well adapted to study forces over large
and continuous fields when the experimental error is sufficiently low and
when the plane of recorded bead deformations is close enough to the
elastomer surface, requirements fulfilled in this experimental study of
Dictyostelium slugs.
Submitted by: Yasuo Maeda [ymaeda@mail.tains.tohoku.ac.jp]
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[End Dicty News, volume 25, number 2] 
