dictyNews
Electronic Edition
Volume 36, number 4
Feb 4, 2011
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Abstracts
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A simple mechanism for complex social behaviour
Katie Parkinson1*, Neil J. Buttery1*, Jason B. Wolf2† and
Christopher R.L. Thompson1†
1 Faculty of Life Sciences, Michael Smith Building, University of Manchester,
Oxford Rd, Manchester, M13 9PT, UK
2 Department of Biology and Biochemistry, University of Bath,
Claverton Down, Bath, BA2 7AY, UK
† Corresponding authors
* These authors contributed equally to this work
PLoS Biology, in press
The evolution of cooperation is a paradox because natural selection should
favour exploitative individuals that avoid paying their fair share of any costs.
Such conflict between the self-interests of cooperating individuals often
results in the evolution of complex, opponent specific, social strategies
and counter strategies. However, the genetic and biological mechanisms
underlying complex social strategies, and therefore the evolution of
cooperative behaviour, are largely unknown. To address this dearth of
empirical data, we combine mathematical modeling, molecular genetic
and developmental approaches to test whether variation in the production
of and response to social signals is sufficient to generate the complex
partner specific social success seen in the social amoeba Dictyostelium
discoideum. Firstly, we find that the simple model of production of and
response to social signals can generate the sort of apparent complex
changes in social behaviour seen in this system, without the need for
partner recognition. Secondly, measurements of signal production and
response in a mutant with a change in a single gene that leads to a shift
in social behaviour provide support for this model. Finally, these simple
measurements of social signalling can also explain complex patterns of
variation in social behaviour generated by the natural genetic diversity
found in isolates collected from the wild. Our studies therefore demonstrate
a novel and elegantly simple underlying mechanistic basis for natural
variation in complex social strategies in D. discoideum. More generally,
they suggest that simple rules governing interactions between individuals
can be sufficient to generate a diverse array of outcomes that appear
complex and unpredictable when those rules are unknown.
Submitted by Chris Thompson [[log in to unmask]]
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Cell type specific filamin complex regulation by a novel class of HECT
ubiquitin ligase is required for normal cell motility and patterning
Simone L. Blagg1, Suzanne Battom1, Sarah J. Annesley2, Thomas Keller1,
Katie Parkinson1, Mei-FangWu1, Paul R. Fisher2 and
Christopher R. L. Thompson1*
1 Faculty of Life Sciences, Michael Smith Building, University of Manchester,
Oxford Road, Manchester M13 9PT, UK
2 Department of Microbiology, La Trobe University, VIC 3086, Australia
* Corresponding Author
Development, in press
Differential cell motility plays a key role in many developmental processes.
This is perhaps most evident in examples of pattern formation in which the
different cell types arise intermingled before sorting out into discrete tissues.
In this, heterogeneities in responsiveness to differentiation inducing signals
are thought to result in the activation of cell type specific genes and ‘salt and
pepper’ patterning. However, how differential gene expression results in cell
sorting is poorly defined. Here we describe a novel gene (hfnA) that provides
the first mechanistic link between cell signalling, differential gene expression
and cell type specific sorting in Dictyostelium. HfnA defines a novel group of
evolutionarily conserved HECT ubiquitin ligases with a Filamin domain
towards the N-terminus (HFNs). HfnA expression is induced by the stalk
differentiation inducing factor DIF-1 and is restricted to a subset of prestalk
cells (pstO). In a HfnA- mutant, pstO cells differentiate but their sorting out is
delayed. Genetic interactions suggest this is due to misregulation of filamin
complex activity. Over-expression of filamin complex members phenocopies
the HfnA- pstO cell sorting defect, whereas disruption of filamin complex
function in a wild type background results in pstO cells sorting more strongly.
Furthermore, filamin disruption in an HfnA- background effectively rescues
pstO cell localization. Finally HfnA- cells also exhibit altered slug phototaxis
phenotypes that are consistent with filamin complex hyperactivity. We
therefore propose that HfnA regulates filamin complex activity and cell type
specific motility, through the breakdown of filamin complexes. These
findings provide a novel mechanism for filamin regulation, and demonstrate
that filamin is a crucial mechanistic link between responses to differentiation
signals and cell movement in patterning based on ‘salt and pepper’
differentiation and sorting out.
Submitted by Chris Thompson [[log in to unmask]]
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Non-genetic heterogeneity and cell fate choice in D. discoideum
Alex Chattwood and Christopher R.L. Thompson*
Faculty of Life Sciences, University of Manchester, Michael Smith Building,
Oxford Rd, Manchester, M13 9PT
*Corresponding author
Development, Growth and Differentiation, in press
From microbes to metazoans, it is now clear that fluctuations in the
abundance of mRNA transcripts and protein molecules enable genetically
identical cells to oscillate between several distinct states (Kaern et al., 2005).
Since this cell-cell variability does not derive from physical differences in
the genetic code it is termed non-genetic heterogeneity. Non-genetic
heterogeneity endows cell populations with useful capabilities they could
never achieve if each cell were the same as its neighbours (Eldar and
Elowitz, 2010; Raj and van Oudenaarden, 2008). One such example is
seen during multicellular development and ‘salt and pepper’ cell type
differentiation. In this review, we will firstly examine the importance of
non-genetic heterogeneity in initiating ‘salt and pepper’ pattern formation
during Dictyostelium discoideum development. Secondly, we will discuss
the various ways in which non-genetic heterogeneity might be generated,
as well as recent advances in understanding the molecular basis of
heterogeneity in this system.
Submitted by Chris Thompson [[log in to unmask]]
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Nucleolar localization and identification of nuclear/nucleolar localization
signals of the calmodulin-binding protein nucleomorphin during growth
and mitosis in Dictyostelium
Andrew Catalano (1) and Danton H. O’Day (2)
(1) Department of Cell & Systems Biology, 25 Harbord Street, University
of Toronto, Toronto, ON, Canada M5S 3G5
(2) Department of Biology, University of Toronto at Mississauga, 3359
Mississauga Road , Mississauga, ON, Canada L5L 1C6
Histochemistry and Cell Biology in press
The calmodulin-binding protein nucleomorphin isoform NumA1 is a nuclear
number regulator in Dictyostelium that localizes to intra-nuclear patches
adjacent to the nuclear envelope and to a lesser extent the nucleoplasm.
Earlier studies have shown similar patches to be nucleoli but only three
nucleolar proteins have been identified in Dictyostelium. Here, actinomycin-D
treatment caused the loss of NumA1 localization while calcium and calmodulin
antagonists had no effect. In keeping with a nucleolar function, NumA1 moved
out of the presumptive nucleoli during mitosis redistributing to areas within the
nucleus, the spindle fibers, and centrosomal region before re-accumulating in
the presumptive nucleoli at telophase. Together these data verify NumA1 as
a true nucleolar protein. Prior to this study the dynamics of specific nucleolar
proteins had not been determined during mitosis in Dictyostelium. FITC-
conjugated peptides equivalent to presumptive nuclear localization signals
within NumA1 localized to nucleoli indicating that they also act as nucleolar
localization signals. To our knowledge these represent the firstprecisely-defined
nucleolar localization signals as well as the first nuclear/nucleolar localization
signals identified in Dictyostelium. Together, these results reveal that NumA1
is a true nucleolar protein and the only nucleolar calmodulin-binding protein
identified in Dictyostelium. Possible use of nuclear/nucleolar localization
signal-mediated drug targeting to nucleoli is discussed.
Submitted by Danton H. O’Day [[log in to unmask]]
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Efficient generation of gene knockout plasmids for Dictyostelium discoideum
using one-step cloning
Stephan Wiegand, Janis Kruse, Sina Gronemann & Christian Hammann
Genomics, in press
The amoeba Dictyostelium discoideum is a well-established model organism
for studying numerous aspects of cellular and developmental functions. Its
rather small (~34 Mb) chromosomal genome and the high efficiency of gene
disruption by homologous recombination have enabled researchers to dissect
various specific gene functions. We describe here the use of one-step cloning
for the fast and efficient generation of deletion vectors that are produced in a
one-step reaction by inserting two PCR products into an organism-specific,
generic acceptor system. This worked efficiently for all 16 tested constructs
directed against genes in the amoeba Dictyostelium discoideum. Saving cost
and time, the used protocol represents a significant advancement in the
generation of such plasmids compared to the conventionally applied restriction
enzyme/ligation approach. Using appropriate selection markers, similar systems
could also be useful in other organisms, where genes can be knocked out by
homologous recombination.
Submitted by Christian Hammann [[log in to unmask]]
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Actin Switches in Phagocytosis
Günther Gerisch
Max-Planck-Institut für Biochemie, 82152 Martinsried, Germany
Communicative & Integrative Biology, in press
Exposure of phagocytes to non-spherical particles has provided evidence
for multiple actions of the actin system in force generation. For the uptake
of long cylindrical particles, a “motile actin clamp” mechanism is proposed.
When a phagocyte is engaged with an hourglass-shaped particle, it exerts
contractile activity alternatively at the far end of the particle or at its concave
region. Phagocytes can switch within seconds between these different
strategies of taking up a particle. This response switching is based on
reprogramming the pattern of actin polymerization and depolymerization.
The choice between different strategies of interaction with a particle
increases the probability of engulfing the entire particle or at least a portion
of it. Finally, a switch to actin disassembly enables a phagocyte to release
a particle that turns out to be too big to be enclosed.
Submitted by: Günther Gerisch [log in to unmask]]
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[End dictyNews, volume 36, number 4]
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