dictyNews
Electronic Edition
Volume 39, number 33
November 29, 2013
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Abstracts
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Interspecies and intraspecies interactions in social amoebae
Santosh Sathe, Neha Khetan and Vidyanand Nanjundiah
Centre for Ecological Sciences and Department of Molecular
Reproduction, Development and Genetics, Indian Institute of Science,
Bangalore- 560012, India.
Corresponding author: Santosh Sathe ([log in to unmask])
Journal of Evolutionary Biology, in press
The stable coexistence of individuals of different genotypes and
reproductive division of labour within heterogeneous groups are of
fundamental interest from the viewpoint of evolution. Cellular slime
moulds are convenient organisms in which to address both issues.
Strains of a species co-occur, and so do different species. As a result
social groups in the wild are often genetically heterogeneous. Generally,
amoebae of strains that participate in genetically mixed groups differ in
the efficiency with which they form spores, which raises questions
regarding the basis of their long-term coexistence. We have carried out
intra- and inter-species 1:1 pair wise mixes between wild isolates of
Dictyostelium giganteum and D. purpureum. Mixing leads to
co-aggregation, after which the constituents of the chimaeric aggregate
sort out to varying extents. On the whole, intra-species aggregates tend to
develop in concert and give rise to chimaeric fruiting bodies in which there
are disproportionately more spores of one component than the other. Inter-
species aggregates exhibit almost complete sorting out and most if not all
spores in a fruiting body belong to a single species. Somatic compatibility
is assessed by successful participation in forming a chimaeric fruiting
body. It is highest within clones, lower among strains of the same species
and lowest between strains of different species. Further, somatic
compatibility is negatively correlated with the variance in the proportions
of spores contributed by either component in the mix. The long-term
coexistence of cellular slime moulds would appear to involve tradeoffs
between fitness-related traits (when strains that co-aggregate belong to
the same species and are compatible, and constitute what we term a
guild), sorting out (when the strains belong to different guilds in the same
species and are incompatible) and avoidance (when strains belong to
different species). We speculate that incompatible guilds of the same
species represent an early step in the splitting of one species into two.
Submitted by Santosh Sathe [[log in to unmask]]
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The arrestin-domain containing protein AdcA is a response element to stress
Habourdin C, Klein G, Araki T, Williams JG, Aubry L.
Cell Communication and Signaling, in press
BACKGROUND:
Cell behaviour is tightly determined by sensing and integration of
extracellular changes through membrane detectors such as receptors
and transporters and activation of downstream signalling cascades.
Arrestin proteins act as scaffolds at the plasma membrane and along
the endocytic pathway, where they regulate the activity and the fate of
some of these detectors. Members of the arrestin clan are widely
present from unicellular to metazoa, with roles in signal transduction
and metabolism. As a soil amoeba, Dictyostelium is frequently
confronted with environmental changes likely to compromise survival.
Here, we investigated whether the recently described arrestin-related
protein AdcA is part of the cell response to stresses.
RESULTS:
Our data provide evidence that AdcA responds to a variety of stresses
including hyperosmolarity by a transient phosphorylation. Analysis in
different mutant backgrounds revealed that AdcA phosphorylation
involves pathways other than the DokA and cGMP-dependent
osmostress pathways, respectively known to regulate PKA and STATc,
key actors in the cellular response to conditions of hyperosmolarity.
Interestingly, however, both AdcA and STATc are sensitive to changes
in the F-actin polymerization status, suggesting a common primary
sensor/trigger and linking the stress-sensitive kinase responsive for
AdcA phosphorylation to the actin cytoskeleton. We also show that
STATc-dependent transcriptional activity is involved for the timely
dephosphorylation of AdcA in cells under stress.
CONCLUSION:
Under osmotic stress, AdcA undergoes a phosphorylation-
dephosphorylation cycle involving a stress-sensitive kinase and the
transcription regulator STATc. This transient post-transcriptional
modification may allow a regulation of AdcA function possibly to
optimize the cellular stress response.
Submitted by Laurence Aubry [[log in to unmask]]
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Developmental lineage priming in Dictyostelium by heterogeneous
Ras activation
Alex Chattwood1,§, Koki Nagayama1,§, Parvin Bolourani2, Lauren
Harkin1, Marzieh Kamjoo1, Gerald Weeks2 and Christopher R.L.
Thompson1*
1 Faculty of Life Sciences, University of Manchester, Michael Smith
Building, Oxford Rd, Manchester, M13 9PT
2 Department of Microbiology and Immunology, University of British
Columbia, Life Sciences Centre, 2350 Health Sciences Mall,
Vancouver BC, V6T 1Z3, Canada
* Corresponding author
§ These authors contributed equally
eLife, in press
In cell culture, genetically identical cells often exhibit heterogeneous
behavior, with only ‘lineage primed’ cells responding to differentiation
inducing signals. It has recently been proposed that such heterogeneity
exists during normal embryonic development to allow position
independent patterning based on ‘salt and pepper’ differentiation and
sorting out. However, the molecular basis of lineage priming and how it
leads to reproducible cell type proportioning is poorly understood. To
address this, we employed a novel forward genetic approach in the
model organism Dictyostelium discoideum. These studies revealed the
Ras-GTPase regulator, gefE, to be required for normal lineage priming
and salt and pepper differentiation. We find that this is because
Ras-GTPase activity sets the intrinsic response threshold to lineage
specific differentiation signals. Importantly, we show that although gefE
expression is uniform, transcription of its target, rasD, is both
heterogeneous and dynamic, thus providing a novel mechanism for
heterogeneity generation and position independent differentiation.
Submitted by Chris Thompson [[log in to unmask]]
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[End dictyNews, volume 39, number 33]
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