dictyNews
Electronic Edition
Volume 36, number 16
June 17, 2011

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Abstracts
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Signalling and Sex in the Social Amoebozoans

Danton H. O’Day and Alex Keszei


Biological Reviews, in press

The social amoebozoans have a life tricycle consisting of asexual multicellular 
development leading to fruiting bodies, sexual multicellular development 
resulting in macrocysts, and unicellular development generating microcysts. 
This review covers the events of sexual development in the most well-studied 
heterothallic (Dictyostelium discoideum) and homothallic (D. mucoroides) 
mating systems. Sexual development begins with pheromonal interactions 
that produce fusion competent cells (gametes) which undergo cell and 
pronuclear fusion. Calcium and calmodulin mediated signalling mediates 
these early events. As they initiate chemotactic signalling, each zygote 
increases in size becoming a zygote giant cell. Using cAMP, the zygote 
chemotactically lures in amoebae and engulfs them in an act of cannibalistic 
phagocytosis. Chemotaxis proceeds more quickly than endocytosis because 
the breakdown products of cAMP (5-AMP, adenosine) bind to a presumptive 
adenosine receptor to inhibit sexual phagocytosis. Zygote giant cells also 
produce several other signalling molecules that feed back to regulate early 
events. The amoebae surrounding the zygote seal their fate as zygotic foodstuff 
y secreting a primary cellulose wall, which prevents their escape. Phagocytosis 
within this precyst continues until all peripheral amoebae are internalized as 
endocytes and the final macrocyst wall is formed. Endocyte digestion results in 
a mature macrocyst with a uniform cytoplasm containing a diploid nucleus. 
After detailing the morphological events of heterothallic and homothallic mating, 
we review the various intercellular signalling events and other mechanisms 
involved in each stage. This complete and comprehensive review sets the 
stage for future research on the unique events that characterize sex in the 
social amoebozoans.


Submitted by Danton O’Day [[log in to unmask]]
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High-resolution X-ray structure of the trimeric Scar/WAVE-complex 
precursor Brk1

Joern Linkner (1,5), Gregor Witte (2,5), Theresia Stradal (3,4),  Ute Curth (1) 
and Jan Faix (1)

1) Institute for Biophysical Chemistry, Hannover Medical School, Hannover, Germany. 
2) Gene Center and Department of Biochemistry, Munich Center for Advanced 
Photonics (MAP) and Center for Integrated Protein Science Munich (CIPSM) at 
the Ludwig-Maximilians-University, Munich, Germany. 
3) Institute for Molecular Cell Biology, University of Muenster, Muenster, Germany. 
4) Signaling and Motility Group, Helmholtz Centre for Infection Research (HZI), 
Braunschweig, Germany 
5) These authors contributed equally to this work


PLoSOne, in press

The Scar/WAVE-complex links upstream Rho-GTPase signaling to the 
activation of the conserved Arp2/3-complex. Scar/WAVE-induced and 
Arp2/3-complex-mediated actin nucleation is crucial for actin assembly 
in protruding lamellipodia to drive cell migration. The heteropentameric 
Scar/WAVE-complex is composed of Scar/WAVE, Abi, Nap, Pir and a 
small polypeptide Brk1/HSPC300, and recent work suggested that free 
Brk1 serves as a homooligomeric precursor in the assembly of this complex. 
Here we characterized the Brk1 trimer from Dictyostelium by analytical 
ultracentrifugation and gelfiltration. We show for the first time its dissociation 
at concentrations in the nanomolar range as well as an exchange of subunits 
within different DdBrk1 containing complexes. Moreover, we determined the 
three-dimensional structure of DdBrk1 at 1.5 Å resolution by X-ray 
crystallography. Three chains of DdBrk1 are associated with each other 
forming a parallel triple coiled-coil bundle. Notably, this structure is highly
similar to the heterotrimeric alpha-helical bundle of HSPC300/WAVE1/Abi2 
within the human Scar/WAVE-complex. This finding together with the fact 
that Brk1 is collectively sandwiched by the remaining subunits, and also 
constitutes the main subunit connecting the triple-coil domain of the 
HSPC300/WAVE1/Abi2/ heterotrimer to Sra1(Pir1), implies a critical 
function of this subunit in the assembly process of the entire complex.


Submitted by Jan Faix [[log in to unmask]]
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Br-DIF-1 accelerates 1% dimethyl sulfoxide-induced cardiomyocyte 
differentiation from P19CL6 embryonic carcinoma cells.

Seya K, Kanemaru K, Matsuki M, Hongo K, Kitahara H, Kikuchi H, 
Oshima Y, Kubohara Y, Okumura K, Motomura S, Furukawa KI.

Department of Pharmacology, Hirosaki University Graduate School of 
Medicine, Hirosaki 036-8562, Japan. etc.


Br. J. Pharmacol., in press

Background and purpose: Stem cell transplantation therapy is a promising 
alternative treatment for severe ischemic heart disease. Although dimethyl 
sulfoxide (DMSO) is known to differentiate P19CL6 embryonic carcinoma cells 
into cardiomyocyte-like cells, the low differentiation capacity of DMSO reduces 
its usefulness. To develop new inducing factors that promote a high degree 
of differentiation, we investigated the effect on P19CL6 cells of derivatives of 
the differentiation-inducing factor-1 (DIF-1), a bioactive compound originally 
found in the cellular slime mould, Dictyostelium discoideum. 

Experimental approach: P19CL6 cells were cultured in alpha-MEM with 
10% FBS including each drug. Drug-induced differentiation was assessed 
by measuring the number of beating and non-beating aggregates, and the 
expression of various genes. The mechanism of action was investigated 
using a T-type Ca(2+) channel blocker. 

Key results: No other DIF-1 derivatives except Br-DIF-1 showed any effects 
on cardiomyocyte differentiation. In the presence of 1% DMSO, Br-DIF-1 
(0.3-3 µM) significantly and dose-dependently increased the number of 
spontaneously beating aggregates compared with 1% DMSO alone on Day 
16. Expression of T-type Ca(2+) channel mRNA was significantly increased 
by Br-DIF-1 + 1% DMSO compared with 1% DMSO alone. Mibefradil 
(a T-type Ca(2+) channel blocker; 100nM) and a small interfering RNA of 
the T-type Ca(2+) channel both significantly decreased the beating rate of 
aggregates induced by Br-DIF-1 + 1% DMSO. 

Conclusions and implications: These results suggest that Br-DIF-1 potently 
accelerates the 1% DMSO-induced differentiation of P19CL6 cells into s
pontaneously beating cardiomyocyte-like cells, partly by enhancing the 
expression of the T-type Ca(2+) channel gene.


Submitted by Yuzuru Kubohara [[log in to unmask]]
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[End dictyNews, volume 36, number 16]