dictyNews
Electronic Edition
Volume 29, number 5
August 10, 2007

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 dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.


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Abstracts
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Spatio-temporal analysis of eukaryotic cell motility by improved force
cytometry

Juan C. del Álamo, Ruedi Meili, Baldomero Alonso-Latorre, Javier
Rodríguez-Rodríguez, Alberto Aliseda, Richard A. Firtel, and Juan C. Lasheras


PNAS, in press

Cell motility plays an essential role in many biological systems, but
precise quantitative knowledge of the bio-physical processes involved in
cell migration is limited. Better measurements are needed to ultimately
build models with predictive capabilities. We present an improved force
cytometry method and apply it to the analysis of the dynamics of the
chemotactic migration of the amoeboid form of Dictyostelium discoideum.
Our explicit calculation of the force field takes into account the finite
thickness of the elastic substrate and improves the accuracy and resolution
compared to previous methods. This enables us to quantitatively study the
differences in the mechanics of the migration of wild-type and mutant cell
lines. The time evolution of the strain energy exerted by the migrating cells
on their substrate is quasi-periodic and can be used as a simple indicator of
the stages of the cell motility cycle. We have found that the mean velocity
of migration v and the period of the strain energy T cycle are related through
a hyperbolic law v = L/T, where L is a constant step length that remains
unchanged in mutants with adhesion or contraction defects. Furthermore,
when cells adhere to the substrate, they exert opposing pole forces that
are orders of magnitude higher than required to overcome the resistance
from their environment.


Submitted by: Rick Firtel [rafirtel@ucsd.edu]
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A fast Ca2+-induced Ca2+-release mechanism in Dictyostelium discoideum

Dieter Malchow, Daniel F. Lusche, Arturo De Lozanne, Christina Schlatterer


Cell Calcium, in press

In vertebrate cells calcium induced calcium release (CICR) is thought to be
responsible for rapid cytosolic Ca2+-elevations despite the occurrence of
strong Ca2+-buffering within the cytosol. In Dictyostelium, a CICR-mechanism
has not been reported. While analyzing Ca2+-regulation in a vesicular fraction
of Dictyostelium rich in Ca2+-flux activity, containing contractile vacuoles (CV)
as the main component of acidic Ca2+-stores and ER, we detected a rapid Ca2+
change upon addition of Ca2+ (CIC). CIC was three times larger in active stores
accumulating Ca2+ than before Ca2+ uptake and in inactivated stores.
Ca2+-release was demonstrated with the calmodulin antagonist W7 that inhibits
the V type H+ATPase activity and Ca2+-uptake of acidic Ca2+-stores. W7 caused
a rapid and large increase of extravesicular Ca2+ ([Ca2+]e), much faster and
larger than thapsigargin (Tg), a Ca2+-uptake inhibitor of the ER. W7 treatment
blocked CIC indicating that a large part of CIC is due to Ca2+-release. The
height of CIC depended on the filling state of the Ca2+-stores. CIC was
virtually unchanged in the iplA  strain that lacks a putative IP3- or ryanodine
receptor thought to be located at the endoplasmic reticulum. By contrast, CIC
was reduced in two mutants, HGR8 and lvsA-, that are impaired in acidic
Ca2+ store function. Purified Ca2+-stores enriched in CV still displayed CIC,
indicating that CV are a source of Ca2+-induced Ca2+-release. CIC-defective
mutants were altered in their oscillatory properties. The irregularity of
the HGR8 oscillation suggests that the principal oscillator is affected in
this mutant.


Submitted by: Christina Schlatterer [Christina.Schlatterer@uni-konstanz.de]
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[End dictyNews, volume 29, number 5]