dictyNews
Electronic Edition
Volume 32, number 16
June 26, 2009
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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 [[log in to unmask]]
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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: [log in to unmask]
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 [[log in to unmask]]
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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 [[log in to unmask]]
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[End dictyNews, volume 32, number 16]
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