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dictyNews Volume 32 Number 16
dictyNews
Electronic Edition
Volume 32, number 16
June 26, 2009
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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Quantification of social behaviour in D. discoideum reveals complex fixed
and facultative strategies
Neil J. Buttery, Daniel E. Rozen, Jason B. Wolf* & Christopher R. L. Thompson*
Faculty of Life Sciences, University of Manchester, Michael Smith Building,
Oxford Rd, Manchester M13 9PT, UK.
*Corresponding authors
Current Biology, in press
The maintenance of cooperation is an evolutionary conundrum because costly
cooperative acts can be exploited by cheaters. Therefore, understanding
cooperation requires an understanding of the nature of cheaters and the
strategies used to mitigate their effects. However, it is often difficult to
determine what accounts for differential social success, thus hindering
empirical investigation of cheating. For example, both fixed and facultative
strategies can contribute to differential success in social interactions.
Furthermore, there is also confusion about how to distinguish social cheating
from other possible causes of unequal success in social situations that can
result in winners and losers without the need for cheating. To study these
problems, we examined the success of naturally occurring genotypes of
Dictyostelium discoideum in social interactions. Upon starvation, different
D. discoideum genotypes will form chimeric fruiting bodies, consisting of dead
stalk cells and viable spores. Here, we demonstrate that an apparent
competitive dominance hierarchy of spore formation in chimera is partly due
to a fixed strategy in which genotypes exhibit dramatic differences in their
inherent allocation to stalk and spores. However, we also demonstrate the
existence of complex facultative social interactions, where genotypes change
their spore/stalk allocation when developed in chimera, with the magnitude
and direction of changes in allocation dependent upon the genotype of their
partner. Using these changes in allocation patterns in chimera, we further
define and partition facultative cheating into two forms: 1) promotion of individual
fitness through selfish behaviour (‘self-promotion’) and 2) coercion of other
individuals (or genotypes) to act cooperatively. Our results demonstrate and
define social interactions between D. discoideum isolates, thus providing a
conceptual framework for the study of the genetic mechanisms that underpin
social evolution.
Submitted by: Chris Thompson [christopher.thompson@manchester.ac.uk]
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Forming Patterns in Development Without Morphogen Gradients: Scattered
Differentiation and Sorting Out
Robert R. Kay1 and Christopher R.L. Thompson2
1MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH
2Faculty of Life Sciences, University of Manchester, Michael Smith Building,
Oxford Road, Manchester M13 9PT
Correspondence: christopher.thompson@manchester.ac.uk
Generation and Interpretation of Morphogenetic Gradients in CSH Perspectives
in Biology
Edited by James Briscoe, Peter Lawrence and Jean-Paul Vincent
Few mechanisms provide alternatives to morphogen gradients for producing spatial
patterns of cells in development. One possibility is based on the sorting out of cells
that initially differentiate in a salt and pepper mixture and then physicallymove to
create coherent tissues. Here we describe the evidence suggesting this is the major
mode of patterning in Dictyostelium. In addition, we discuss whether convergent
evolution could have produced a conceptually similar mechanism in other organisms.
Submitted by: Chris Thompson [christopher.thompson@manchester.ac.uk]
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Dictyostelium Sun1 is a dynamic membrane protein of both nuclear membranes
and required for centrosomal association with clustered centromeres
Irene Schulz, Otto Baumann, Matthias Samereier, Christine Zoglmeier, Ralph Gräf*
University of Potsdam, Dept. of Cell Biology, 14476 Potsdam-Golm, Germany
Journal: it is Eur. J. Cell Biol., in press
Centrosomal attachment to nuclei is crucial for proper mitosis and nuclear
positioning in various organisms, and generally involves SUN-family proteins
located at the inner nuclear envelope. There is still no common scheme for
the outer nuclear membrane proteins interacting with SUN1 in
centrosome/nucleus attachment. Here we propose a model in which Sun1
mediates a physical link between centrosomes and clustered centromeres
through both nuclear membranes in Dictyostelium. For the first time we provide
a detailed microscopic analysis of the centrosomal and nuclear envelope
localization of endogenous Dictyostelium Sun1 during interphase and mitosis.
By immunogold electron microscopy we show that Sun1 is a resident of both
nuclear membranes. Disruption of Sun1 function by overexpression of full length
GFP-Sun1 or a GFP-SUN-domain deletion construct revealed not only the
established function in centrosome/nucleus attachment and maintenance of
ploidy, but also a requirement of Sun1 for the association of the centromere
cluster with the centrosome. Live cell imaging visualized the occurrence of mitotic
defects, and demonstrated the requirement of microtubules for dynamic distance
changes between centrosomes and nuclei. FRAP analysis revealed at least two
populations of Sun1, with an immobile fraction associated with the centrosome,
and a mobile fraction in the nuclear envelope.
Submitted by: Ralph Gräf [rgraef@RZ.UNI-POTSDAM.DE]
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[End dictyNews, volume 32, number 16]
