dictyNews
Electronic Edition
Volume 44, number 14
May 11, 2018
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Abstracts
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Glycogen synthase kinase 3 promotes multicellular development
over unicellular encystation in encysting Dictyostelia
Yoshinori Kawabe1,2*, Takahiro Morio2, Yoshimasa Tanaka2, and
Pauline Schaap1
1School of Life Sciences, University of Dundee, Dundee, DD15EH, UK
2Graduate School of Life and Environmental Sciences, University of
Tsukuba, Ibaraki, 305-8572, Japan
EvoDevo, in press
Background: Glycogen synthase kinase 3 (GSK3) regulates many cell
fate decisions in animal development. In multicellular structures of the
group 4 dictyostelid Dictyostelium discoideum, GSK3 promotes spore
over stalk-like differentiation. We investigated whether, similar to other
sporulation inducing genes such as cAMP dependent protein kinase
(PKA), this role of GSK3 is derived from an ancestral role in encystation
of unicellular amoebas.
Results: We deleted GSK3 in Polysphondylium pallidum, a group 2
dictyostelid which has retained encystation as an alternative survival
strategy. Loss of GSK3 inhibited cytokinesis of cells in suspension, as
also occurs in D. discoideum, but did not affect spore or stalk
differentiation in P. pallidum. However, gsk3- amoebas entered into
encystation under conditions that in wild-type favour aggregation and
fruiting body formation. The gsk3- cells were hypersensitive to
osmolytes, which are known to promote encystation, and to cyst
inducing factors that are secreted during starvation. GSK3 was not
itself regulated by these factors, but inhibited their effects.
Conclusions: Our data show that GSK3 has a deeply conserved role
in controlling cytokinesis, but not spore differentiation in Dictyostelia.
Instead, in P. pallidum, one of many Dictyostelia that like their solitary
ancestors can still encyst to survive starvation, GSK3 promotes
multicellular development into fruiting bodies over unicellular encystment.
submitted by: Pauline Schaap [[log in to unmask]]
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Strategic investment explains patterns of cooperation and cheating in
a microbe
Philip G. Madgwick1†, Balint Stewart2†, Laurence J. Belcher1,
Christopher R.L. Thompson2*, and Jason B. Wolf1*
1 Milner Centre for Evolution and Department of Biology and Biochemistry,
University of Bath, Claverton Down, Bath, BA2 7AY, UK
2 Centre for Life's Origins and Evolution, Department of Genetics, Evolution
and Environment, University College London, Darwin Building, Gower Street,
London, WC1E 6BT, UK
* Correspondence to: [log in to unmask] and
[log in to unmask]
† These authors contributed equally to this work
PNAS, in press
Contributing to cooperation is typically costly, while its rewards are often
available to all members of a social group. So why should individuals be
willing to pay these costs, especially if they could cheat by exploiting the
investments of others? Kin selection theory broadly predicts that individuals
should invest more into cooperation if their relatedness to group members is
high (assuming they can discriminate kin from non-kin). To better understand
how relatedness affects cooperation, we derived the ‘Collective Investment’
game, which provides quantitative predictions for patterns of strategic
investment depending on the level of relatedness. We then tested these
predictions by experimentally manipulating relatedness (genotype frequencies)
in mixed cooperative aggregations of the social amoeba Dictyostelium
discoideum, which builds a stalk to facilitate spore dispersal. Measurements of
stalk investment by natural strains correspond to the predicted patterns of
relatedness-dependent strategic investment, wherein investment by a strain
increases with its relatedness to the group. Furthermore, if overall group
relatedness is relatively low (i.e., no strain is at high frequency in a group)
strains face a scenario akin to the ‘Prisoner’s Dilemma’ and suffer from
insufficient collective investment. We find that strains employ relatedness-
dependent segregation to avoid these pernicious conditions. These findings
demonstrate that simple organisms like D. discoideum are not restricted to
being ‘cheaters’ or ‘cooperators’, but instead measure their relatedness to their
group and strategically modulate their investment into cooperation accordingly.
Consequently, all individuals will sometimes appear to cooperate and
sometimes cheat due to the dynamics of strategic investing.
submitted by: Chris Thompson [[log in to unmask]]
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A G-protein-coupled chemoattractant receptor recognizes lipopolysaccharide
for bacterial phagocytosis
Miao Pan, Matthew P. Neilson, Alexander M. Grunfeld, Phillip Cruz, Xi Wen,
Robert H. Insall, and Tian Jin
PLoS Biology, in press
Phagocytes locate microorganisms via chemotaxis, then consume them
using phagocytosis. Dictyostelium amoebas are stereotypical phagocytes
that prey on diverse bacteria using both processes. However, as typical
phagocytic receptors, such as complement receptors or Fcƒ× receptors,
have not been found in Dictyostelium, it remains mysterious how these
cells recognize bacteria. Here, we show that a single G-protein-coupled
receptor, fAR1, simultaneously recognizes the chemoattractant folate and
the phagocytic cue lipopolysaccharide, a major component of bacterial
surfaces. Cells lacking fAR1 or its cognate G-proteins are defective in
chemotaxis toward folate and phagocytosis of Klebsiella aerogenes.
Computational simulations combined with experiments show that responses
associated with chemotaxis can also promote engulfment of particles coated
with chemoattractants. Finally, the extracellular Venus-Flytrap domain of
fAR1 acts as the binding site for both folate and lipopolysaccharide. Thus,
fAR1 represents a new member of the pattern recognition receptors and
mediates signaling from both bacterial surfaces and diffusible
chemoattractants to reorganize actin for chemotaxis and phagocytosis.
submitted by: Miao Pan [[log in to unmask]]
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[End dictyNews, volume 44, number 14]
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