dictyNews
Electronic Edition
Volume 38, number 2
January 13, 2012

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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 [[log in to unmask]]
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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 [[log in to unmask]]
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[End dictyNews, volume 38, number 2]