dictyNews
Electronic Edition
Volume 33, number 2
July 17, 2009

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
useful information is available at dictyBase - http://dictybase.org.

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


The trishanku gene and terminal morphogenesis in Dictyostelium discoideum

Nameeta Mujumdar1, Kei Inouye2 and Vidyanand Nanjundiah1

1Indian Institute of Science, Bangalore, India and 2Kyoto University, Kyoto, 
Japan


Evolution & Development, in press

The positioning of spores relative to the stalk is a characteristic feature 
of morphogenesis in the cellular slime moulds. In Dictyostelium discoideum 
the rising non-motile spore mass is cradled above and below by tissues 
derived from both prestalk cells and anterior-like cells, that are known 
as the upper and lower cup respectively. Trishanku (triA) is a novel 
gene expressed in posterior prespore cells of the D. discoideum slug; 
in the absence of triA function prespore cells halt their ascent midway 
on the stalk (Jaiswal et al., Differentiation 74:596–607, 2006). 
Intra- and inter-strain grafting experiments were carried out with 
anterior and posterior fragments of Ax2 and triA- slugs. Intra-triA- 
grafts show that (a) cells freely cross the prestalk-prespore boundary 
and change their fates accordingly and (b) the lower cup is normal but 
the upper cup is not. The aberrant terminal morphogenesis seen in 
triA- can be traced to the improper functioning of the upper cup. 
When wild-type upper cup function is supplied via other cells, trishanku 
spores can reach the tip of the stalk. Conversely, Ax2 spores fail to 
do so in chimeras in which the upper cup is largely made up of mutant 
cells. A lowered level of expression of the gene encoding the cell 
adhesion molecule lagC during culmination could be responsible for 
the poor attachment of the upper cup to the spore mass in triA- . 
These observations reinforce Sternfeld’s finding (Dev Genes Evol 
208:487–494, 1998) that the wild-type phenotype of the upper cup is 
important for the elevation of the spores in D. discoideum. Further, 
they show that a gene that is expressed in one cell type elicits 
behaviour in a second cell type that can ‘feed back’ and enhance the 
fitness of the first cell type. 


Submitted by Vidyanand Nanjundiah [vidya@ces.iisc.ernet.in]
--------------------------------------------------------------------------------


Yersinia outer protein YopE affects the actin cytoskeleton in Dictyostelium 
discoideum through targeting of multiple Rho family GTPases 

Georgia Vlahou, Oxana Schmidt, Bettina Wagner, Handan Uenlue, 
Petra Dersch, Francisco Rivero and Barbara A. Weissenmayer


BMC Microbiology, in press

Background 
All human pathogenic Yersinia species share a virulence-associated 
type III secretion system that translocates Yersinia effector proteins 
into host cells to counteract infection-induced signaling responses and 
prevent phagocytosis. Dictyostelium discoideum has been recently used to 
study the effects of bacterial virulence factors produced by internalized 
pathogens. In this study we explored the potential of Dictyostelium as 
model organism for analyzing the effects of ectopically expressed Yersinia 
outer proteins (Yops). 

Results
TheYersinia pseudotuberculosis virulence factors YopE, YopH, YopM and 
YopJ were expressed de novo within Dictyostelium and their effects on 
growth in axenic medium and on bacterial lawns were analyzed. No severe 
effect was observed for YopH, YopJ and YopM, but expression of YopE, 
which is a GTPase activating protein for Rho GTPases, was found to be 
highly detrimental. GFP-tagged YopE expressing cells had less conspicuous 
cortical actin accumulation and decreased amounts of F-actin. The actin 
polymerization response upon cAMP stimulation was impaired, although 
chemotaxis was unaffected. YopE also caused reduced uptake of yeast 
particles. These alterations are probably due to impaired Rac1 activation. 
We also found that YopE predominantly associates with intracellular 
membranes including the Golgi apparatus and inhibits the function of 
moderately overexpressed RacH. 

Conclusion 
The phenotype elicited by YopE in Dictyostelium can be explained, at 
least in part, by inactivation of one or more Rho family GTPases. It 
further demonstrates that the social amoeba Dictyostelium discoideum 
can be used as an efficient and easy-to-handle model organism in order 
to analyze the function of a translocated GAP protein of a human pathogen.


Submitted by: Barbara A. Weissenmayer [barbara.weissenmayer@ucd.ie]
==============================================================
[End dictyNews, volume 33, number 2]