dictyNews
Electronic Edition
Volume 40, number 31
December 12, 2014
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Abstracts
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The Dictyostelium prestalk inducer Differentiation Inducing Factor-1
(DIF-1) triggers unexpectedly complex global phosphorylation changes
Chris Sugden*, Michael D. Urbaniak@, Tsuyoshi Araki* and
Jeffrey G. Williams*
*The College of Life Sciences, University of Dundee, Dow St.,
Dundee DD1 5EH, UK.
@Division of Biomedical and Life Sciences, Faculty of Health and
Medicine, Lancaster University, Bailrigg, Lancaster LA1 4YG, UK.
Address correspondence to: Jeffrey G. Williams ([log in to unmask])
Abbreviations: DIF-1, Differentiation Inducing Factor-1; SILAC,
Stable Isotope Labeling by Amino Acids in Cell Culture
Mol Biol of the Cell (MBoC), in press
DIF-1 is a polyketide that induces Dictyoselium amoebae to
differentiate as prestalk cells. We performed a global quantitative
screen for phosphorylation changes that occur within the first minutes
after addition of DIF-1 using a triple-label SILAC approach. This
revealed a new world of DIF-1 controlled signalling: with changes in
components of the MAPK and protein kinase-B signalling pathways,
components of the actinomyosin cytoskeletal signalling networks and
in a broad range of small GTPases and their regulators. The results
also provide evidence that the Ca2+/calmodulin dependent phosphatase
calcineurin plays a role in DIF-1 signalling to the DimB prestalk
transcription factor. At the global level DIF-1 causes a major shift
in the phosphorylation/dephosphorylation equilibrium towards net
dephosphorylation. Interestingly, many of the sites that are
dephosphorylated in response to DIF-1 are phosphorylated in response
to extracellular cAMP signalling. This accords with studies that
suggest an antagonism between the two inducers and also with the rapid
dephosphorylation of the cAMP receptor that we observe in response to
DIF-1 and with the known inhibitory effect of DIF-1 on chemotaxis to
cAMP.
Submitted by Jeff Williams [[log in to unmask]]
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Image based validation of dynamical models for cell reorientation
Robert Lockley (1), Graham Ladds (2) and Till Bretschneider (1)
1 Warwick Systems Biology Centre, Senate House, University of Warwick,
Coventry, United Kingdom
2 Division of Biomedical Cell Biology, Warwick Medical School,
University of Warwick, Coventry, United Kingdom
Cytometry A, first published online (open access): 9 DEC 2014
DOI: 10.1002/cyto.a.22600
A key feature of directed cell movement is the ability of cells to
reorient quickly in response to changes in the direction of an
extracellular stimulus. Mathematical models have suggested quite
different regulatory mechanisms to explain reorientation, raising the
question of how we can validate these models in a rigorous way. In
this study, we fit three reaction–diffusion models to experimental
data of Dictyostelium amoebae reorienting in response to alternating
gradients of mechanical shear flow. The experimental readouts we use
to fit are spatio-temporal distributions of a fluorescent reporter for
cortical F-actin labeling the cell front. Experiments performed under
different conditions are fitted simultaneously to challenge the models
with different types of cellular dynamics. Although the model proposed
by Otsuji is unable to provide a satisfactory fit, those suggested by
Meinhardt and Levchenko fit equally well. Further, we show that
reduction of the three-variable Meinhardt model to a two-variable model
also provides an excellent fit, but has the advantage of all parameters
being uniquely identifiable. Our work demonstrates that model selection
and identifiability analysis, commonly applied to temporal dynamics
problems in systems biology, can be a powerful tool when extended to
spatio-temporal imaging data.
Submitted by Till Bretschneider [[log in to unmask]]
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c-di-GMP induction of Dictyostelium cell death requires the polyketide
DIF-1
Yu Song, Marie-Francoise Luciani, Corinne Giusti, and Pierre Golstein
Centre d’Immunologie de Marseille-Luminy, UM2 Aix-Marseille Universite,
Case 906, 13288 Marseille cedex 9, France;
INSERM, U1104, 13288 Marseille, France;
CNRS, UMR7280, 13288 Marseille, France.
Address correspondence to: Pierre Golstein ([log in to unmask])
Mol Biol of the Cell (MBoC), in press
Cell death in the model organism Dictyostelium, as studied in monolayers
in vitro, can be induced by the polyketide DIF-1 or by the cyclic
dinucleotide c-di-GMP. c-di-GMP, a universal bacterial second messenger,
can trigger innate immunity in bacterially-infected animal cells, and is
involved in developmental cell death in Dictyostelium. We show here that
c-di-GMP was not sufficient to induce cell death in Dictyostelium cell
monolayers. Unexpectedly, it also required the DIF-1 polyketide. The
latter could be exogenous, as revealed by a telling synergy between
c-di-GMP and DIF-1. The required DIF-1 polyketide could also be
endogenous, as shown by the inability of c-di-GMP to induce cell death
in Dictyostelium HMX44A cells and DH1 cells upon pharmacological or
genetic inhibition of DIF-1 biosynthesis. In these cases c-di-GMP-induced
cell death was rescued by complementation with exogenous DIF-1.
Altogether, these results demonstrated that c-di- GMP could trigger cell
death in Dictyostelium only in the presence of the DIF-1 polyketide or
its metabolites. This identified another element of control to this cell
death and perhaps also to c-di-GMP effects in other situations and
organisms.
Submitted by Pierre Golstein [[log in to unmask]]
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[End dictyNews, volume 40, number 31]
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