dictyNews
Electronic Edition
Volume 38, number 16
June 29, 2012

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=========
Abstracts
=========


Mind the gap: a comparative study of migratory behavior in 
social amoebae

Owen M. Gilbert, Jennie J. Kuzdzal-Fick, David C. Queller, 
Joan E. Strassmann


Behavioral Ecology and Sociobiology, in press

Social amoebae aggregate to form a multicellular slug that 
migrates some distance.  Most species produce a stalk during 
migration, but some do not.  We show that D. giganteum, a 
species that produces stalk during migration, is able to traverse 
small gaps and utilize bacterial resources following gap traversal 
by shedding live cells.  In contrast, we found D. discoideum, a 
species that does not produce stalk during migration, can 
traverse gaps only when in the presence of other species’ stalks, 
or other thin filaments.  These findings suggest production of 
stalk during migration allows traversal of gaps, as commonly 
occur in soil and leaf litter.  Considering the functional 
consequences of a stalked migration may be important for 
explaining the evolutionary maintenance or loss of a stalked 
migration.


Submitted by Owen Gilbert [[log in to unmask]]
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Dictyostelium uses the prokaryote messenger c-di-GMP to trigger  
stalk cell differentiation.

Zhi-hui Chen and Pauline Schaap*

College of Life Sciences, University of Dundee, Dundee  DD15EH, 
UK


Nature, in press

Cyclic di-(3’:5’)-guanosine monophosphate (c-di-GMP) is a major 
prokaryote signalling intermediate, which is synthesized by 
diguanylate cyclases and triggers sessility and biofilm formation. 
We detected the first eukaryote diguanylate cyclases (DgcAs) in 
all major groups of Dictyostelia. Upon food depletion, 
Dictyostelium discoideum amoebas collect into aggregates, which 
first transform into migrating slugs and next into sessile fruiting 
structures. These structures consist of a spherical spore mass 
that is supported by a column of stalk cells and a basal disk. A 
polyketide, DIF-1, was isolated earlier, which induces stalk-like 
cells in vitro. However, its role in vivo proved recently to be 
restricted to basal disk formation. Here we show that Dictyostelium 
DgcA produces c-di-GMP as the morphogen responsible for stalk 
cell differentiation.  D.discoideum DgcA synthesized c-di-GMP in 
a GTP-dependent manner and was expressed at the slug tip, the 
site of stalk cell differentiation. Disruption of the DgcA gene 
blocked the transition from slug migration to fructification and the 
expression of stalk genes. Fructification and stalk formation were 
restored by exposing dgca- slugs to wild-type secretion products 
or to c-di-GMP. Moreover, c-di-GMP, but not c-di-AMP, induced 
stalk gene expression in dilute cell monolayers. Apart from 
identifying the long elusive stalk-inducing morphogen, our work 
also identifies the first role for c-di-GMP in eukaryotes. 


Submitted by Pauline Schaap [[log in to unmask]]
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Structured growth and genetic drift raise relatedness in the social 
amoeba Dictyostelium discoideum.

Neil J. Buttery(1), Chandra N. Jack(2), Boahemaa Adu-Oppong(1), 
Kate T. Snyder(3), Christopher R.L. Thompson(4), David C. Queller(1) 
and Joan E. Strassmann(1)

(1) Department of Biology, Campus Box 1137, Washington University 
in Saint Louis, One Brookings Drive, Saint Louis, Missouri, USA
(2) Department of Bioengineering, Rice University, 6100 Main Street, 
Houston, Texas, USA
(3) Department of Ecology and Evolution, Rice University, 6100 
Main Street, Houston, Texas, USA
(4) Faculty of Life Sciences, University of Manchester, 
Oxford Road, Manchester, UK


Biology Letters, in press

One condition for the evolution of altruism is genetic relatedness 
between altruist and beneficiary, often achieved through active kin 
recognition. Here we investigate the power of a passive process 
resulting from genetic drift during population growth in the social 
amoeba Dictyostelium discoideum. We put labelled and unlabelled 
cells of the same clone in the centre of a plate, and allowed them 
to proliferate outward.  Zones formed by genetic drift, due to the 
small population of actively growing cells at the colony edge. We 
also found that single cells could form zones of high relatedness. 
Relatedness increased at a significantly higher rate when food 
was in short supply. This study shows that relatedness can be 
significantly elevated before the social stage without a small 
founding population size or recognition mechanism. 


Submitted by Neil Buttery [[log in to unmask]]
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Innate Non_Specific Cell Substratum Adhesion 

Loomis, W.F., Fuller, D., Gutierrez, E., Groisman, A., 
and Rappel, W-J. 

Section of Cell and Developmental Biology, Division of Biological Sciences,  
Department of Physics, Center for Theoretical Biological Physics 
University of California, San Diego , La Jolla, CA


PLoS ONE, in press

Adhesion of motile cells to solid surfaces is necessary to transmit forces 
required for propulsion. Unlike mammalian cells, Dictyostelium cells do 
not make integrin mediated focal adhesions. Nevertheless, they can 
move rapidly on both hydrophobic and hydrophilic surfaces. We have 
found that adhesion to such surfaces can be inhibited by addition of 
sugars or amino acids to the buffer. Treating whole cells 
with _-mannosidase to cleave surface oligosaccharides also reduces 
adhesion. The results indicate that adhesion of these cells is mediated 
by van der Waals attraction of their surface glycoproteins to the 
underlying substratum. Since glycoproteins are prevalent components 
of the surface of most cells, innate adhesion may be a common
cellular property that has been overlooked.


Submitted by Bill Loomis [[log in to unmask]]
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[End dictyNews, volume 38, number 16]