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dictyNews Volume 38 Number 02
dictyNews
Electronic Edition
Volume 38, number 2
January 13, 2012
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of dictyNews, the Dicty Reference database and other
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Abstracts
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Perturbations of the actin cytoskeleton activate a Dictyostelium
STAT signalling pathway
Tsuyoshi Araki and Jeffrey G. Williams
European Journal of Cell Biology (short communication)
The Dictyostelium transcription factor STATc is tyrosine
phosphorylated and accumulates in the nucleus when cells
are exposed either to hyper-osmotic stress or to the prestalk-
inducing polyketide DIF-1. In the case of stress STAT activation
is mediated by regulated dephosphorylation; whereby two serine
residues on PTP3, the tyrosine phosphatase that de-activates
STATc, become phosphorylated after exposure to stress so
inhibiting enzymatic activity. We now show that the more highly
regulated of the two PTP3 serine residues, S747, is also
phosphorylated in response to DIF-1, suggesting a common
activation mechanism. Hyper-osmotic stress causes a
re-distribution of F-actin to the cortex, cell rounding and
shrinkage and we show that DIF-1 induces a similar but transient
F-actin re-distribution and rounding response. We also find that
two mechanistically distinct inhibitors of actin polymerization,
latrunculin A and cytochalasin A, induce phosphorylation at
S747 of PTP3 and activate STATc. We suggest that PTP3
phosphorylation, and consequent STATc activation, are regulated
by changes in F-actin polymerization status during stress and
DIF-induced cytoskeletal remodelling.
Submitted by jeff williams [j.g.williamd@dundee.ac.uk]
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Ectopic expression of Cyclase associated protein CAP restores the
streaming and aggregation defects of Adenylyl Cyclase A deficient
Dictyostelium discoideum cells.
Sultana, H., Neelakanta, G., Rivero, F., Blau-Wasser, R., Schleicher,
M., Noegel, A A.
BMC Dev. Biol.
Background: Cell adhesion, an integral part of D. discoideum
development, is important for morphogenesis and regulated gene
expression in the multicellular context and is required to trigger
cell-differentiation. G-protein linked adenylyl cyclase pathways are
crucially involved and a mutant lacking the aggregation specific
adenylyl cyclase ACA does not undergo multicellular development.
Results: Here, we have investigated the role of cyclase-associated
protein (CAP), an important regulator of cell polarity and F-actin/G-actin
ratio in the aca mutant. We show that ectopic expression of GFP-CAP
improves cell polarization, streaming and aggregation in aca- cells, but
it fails to completely restore development. Our studies indicate a
requirement of CAP in the ACA dependent signal transduction for
progression of the development of unicellular amoebae into multicellular
structures. The reduced expression of the cell adhesion molecule
DdCAD1 together with csA is responsible for the defects in aca- cells
to initiate multicellular development. Early development was restored
by the expression of GFP-CAP that enhanced the DdCAD1 transcript
levels and to a lesser extent the csA mRNA levels.
Conclusions: Collectively, our data shows a novel role of CAP in
regulating cell adhesion mechanisms during development that might
be envisioned to unravel the functions of mammalian CAP during
animal embryogenesis.
Submitted by Angelika Noegel [noegel@uni-koeln.de]
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[End dictyNews, volume 38, number 2]
