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dictyNews Volume 37 Number 16
dictyNews
Electronic Edition
Volume 37, number 16
December 16, 2011
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
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Abstracts
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The IplA Ca++ Channel Of Dictyostelium discoideum Is Necessary For
Ca++, Not cAMP, Chemotaxis, And Plays A Fundamental Role In Natural
Aggregation
Daniel F. Lusche, Deborah Wessels, Amanda Scherer, Karla Daniels,
Spencer Kuhl and David R. Soll
W.M. Keck Dynamic Image Analysis Facility
Department of Biology, University of Iowa,
Iowa City, IA 52242
J. Cell Science, in press
During aggregation of Dictyostelium discoideum, nondissipating, symmetric,
outwardly moving waves of cAMP direct cells towards aggregation centers.
It has been assumed that the spatial and temporal characteristics of the front
and back of each cAMP wave regulate both chemokinesis and chemotaxis.
However, during the period preceding aggregation, cells acquire not only the
capacity to chemotax in a spatial gradient of cAMP, but also in a spatial
gradient of Ca++. The null mutant of the putative iplA Ca++ channel gene,
iplA-, undergoes normal chemotaxis in spatial gradients of cAMP and normal
chemokinetic responses to increasing temporal gradients of cAMP, both
generated in vitro. However, iplA- cells lose the capacity to undergo
chemotaxis in response to a spatial gradient of Ca++, suggesting that IplA
is either the Ca++ chemotaxis receptor or an essential component of the
Ca++ chemotaxis regulatory pathway. In response to natural chemotactic
waves generated by wild type cells, the chemokinetic response of iplA- cells
to the temporal dynamics of the cAMP wave is intact, but the capacity to
reorient in the direction of the aggregation center at the onset of each wave
is lost. These results suggest a model in which transient Ca++ gradients
formed between cells at the onset of each natural cAMP wave augment
reorientation towards the aggregation center. If this hypothesis proves
correct, it will provide a more complex contextual framework for
interpreting D. discoideum chemotaxis.
Submitted by Deborah Wessels [deborah-wessels@uiowa.edu]
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Incoherent Feedforward Control Governs Adaptation of Activated
Ras in a Eukaryotic Chemotaxis Pathway
Kosuke Takeda, Danying Shao, Micha Adler, Pascale G. Charest,
William F. Loomis, Herbert Levine, Alex Groisman, Wouter-Jan Rappel
and Richard A. Firtel.
Section of Cell and Developmental Biology, Division of Biological
Sciences, and Department of Physics
Science Signaling, in press
Adaptation in signaling systems, during which the output returns to a
fixed base-amount following a change in the input, often involves negative
feedback loops and plays a crucial role in eukaryotic chemotaxis. We
determined the dynamical response of a eukaryotic chemotaxis pathway
immediately downstream from G protein-coupled receptors following a
uniform change in chemoattractant concentration. We found that the
response of an activated Ras shows near perfect adaptation. We
attempted to fit the results using mathematical models for the two possible
simple network topologies that can provide perfect adaptation. Only the
incoherent feedforward network was able to accurately describe the
experimental results. This analysis revealed that adaptation in this Ras
pathway is achieved through the proportional activation of upstream
components and not through negative feedback loops. Furthermore,
these results are consistent with a local excitation, global inhibition
mechanism for gradient sensing, possibly with a RasGAP as a global
inhibitor.
Submitted by Bill Loomis [wloomis@ucsd.edu]
--------------------------------------------------------------------------------------
High relatedness is necessary and sufficient to maintain multicellularity
in Dictyostelium
Jennie J. Kuzdzal-Fick 1,2, Sara A. Fox 1, Joan E. Strassmann 1,3,
David C. Queller 1,3
1 Department of Ecology and Evolutionary Biology, Rice University,
6100 Main Street, Houston, TX 77005
2 Section of Integrative Biology, College of Natural Sciences, The
University of Texas at Austin, University Station C0930, Austin, TX 78712
3 Department of Biology CB1137, Washington University in St. Louis,
One Brookings Drive, St. Louis, MO 63130
Science 16 December 2011, Vol. 334 no. 6062 pp. 1548-1551,
DOI: 10.1126/science.1213272
One sentence summary: Experimental evolution studies show that the
extraordinary cooperation of cells in multicellular organisms degrades
under low relatedness, but is preserved under the high relatedness
generated by single-cell bottlenecks in the life cycle.
Abstract. Most complex multicellular organisms develop clonally from
a single cell. This should limit conflicts between cell lineages that
could threaten the extensive cooperation of cells within multicellular
bodies. Cellular composition can be manipulated in the social amoeba
Dictyostelium discoideum, allowing us to test and confirm the two key
predictions of this theory. Experimental evolution at low relatedness
favored cheating mutants that could destroy multicellular development.
However, under high relatedness the forces of mutation and within-
individual selection are too small for these destructive cheaters to
spread as shown by a mutation accumulation experiment. Thus we
conclude that the single-cell bottleneck is a powerful stabilizer of
cellular cooperation in multicellular organisms.
Submitted by Jennie Kuzdzal-Fick [kuzdzalfick@mail.utexas.edu]
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[End dictyNews, volume 37, number 16]
