dictyNews
Electronic Edition
Volume 36, number 14
May 13, 2011

Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to [log in to unmask]
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.

Follow dictyBase on twitter:
http://twitter.com/dictybase


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


The polyketide MPBD initiates the SDF-1 signaling cascade that 
coordinates terminal differentiation in Dictyostelium

Christophe Anjard, Yongxuan Su and William F. Loomis
Cell and Developmental Biology, Division of Biological Sciences,
University of California San Diego, La Jolla, CA 92093-0368


Eukaryotic Cell, in press

Dictyostelium uses a wide array of chemical signals to coordinate 
differentiation as it switches from a unicellular to a multicellular 
organism. MPBD, the product of the polyketide synthase encoded 
by stlA, regulates stalk and spore differentiation by rapidly 
stimulating the release of the phospho-peptide SDF-1. By 
analyzing specific mutants affected in MPBD or SDF-1 production, 
we delineated a signal transduction cascade through the membrane 
receptor CrlA coupled to Ga1, leading to the inhibition of GskA such 
that the precursor of SDF-1 is released. It is then processed by the
extracellular protease of TagB on prestalk cells. SDF-1 apparently 
acts through the adenylyl cyclase ACG to activate the cAMP 
dependent protein kinase PKA and trigger the production of more 
SDF-1. This signaling cascade shows similarities with the SDF-2 
signalling pathway that acts later to induce a rapid spore encapsulation.


Submitted by  Bill Loomis [[log in to unmask]]
--------------------------------------------------------------------------------


Autonomous and non-autonomous traits mediate social cooperation in
Dictyostelium discoideum

Nameeta Mujumdar(1,#), Ashvini Kumar Dubey(2), Krithi Nandimath(1) and
Vidyanand Nanjundiah (1, 2)

(1) Indian Institute of Science and (2)Jawaharlal Nehru Centre for
Advanced Scientific Research, Bangalore 560012, India. (#)Present address:
Division of Basic and Translational Research, University of Minnesota,
Minneapolis, MN 55455, USA.


Journal of Biosciences, in press

In the trishanku (triA-) mutant of Dictyostelium discoideum aggregates are
smaller than usual and the spore mass is located mid-way up the stalk, not
at the apex. We have monitored aggregate territory size, spore allocation
and fruiting body morphology in chimaeric groups of Ax2 and triA- cells.
Developmental canalisation breaks down in chimaeras. A minority of triA-
cells causes largely Ax2 aggregation streams to break up; the effect is
not due to counting factor. Most chimaeric fruiting bodies resemble those
of Ax2 or triA-. Others are double-deckers with a single stalk and two
spore masses, one each at the terminus and mid-way along the stalk. The
relative number of spores belonging to the two genotypes depends on the
mixing ratio and fruiting body morphology. In double-deckers formed from
1:1 chimaeras the upper spore mass has more Ax2 spores, and the lower
spore mass more triA- spores, than expected. Thus the traits under study
depend partly on the cells’ own genotype and partly on the phenotypes, and
so genotypes, of other cells: they are both autonomous and non-autonomous.
These findings strengthen the parallels between multicellular development
and behaviour in social groups. Besides that, they reinforce the point
that particular traits can be associated with genotypes only in a specific
context.


Submitted by Vidyanand Nanjundiah [[log in to unmask]]
--------------------------------------------------------------------------------


Alteration of virulence factors and rearrangement of pAsa5 plasmid caused 
by the growth of Aeromonas salmonicida in stressful conditions

Rana K. Daher1,2, Geneviève Filion1,2, Sok Gheck E. Tan2, Stéphanie 
Dallaire-Dufresne1,2, Valérie E. Paquet1,2 and Steve J. Charette1,2,3* 
 
1. Institut de biologie intégrative et des systèmes, Pavillon Charles-Eugène-
Marchand, Université Laval, 1030 avenue de la Médecine, Quebec City, 
Quebec, Canada, G1V 0A6
2. Centre de recherche de l’Institut universitaire de cardiologie et de 
pneumologie de Québec (Hôpital Laval), 2725 Chemin Sainte-Foy, 
Quebec City, Quebec, Canada, G1V 4G5
3. Département de biochimie, de microbiologie et de bio-informatique, 
Faculté des sciences et de génie, Université Laval, 1045 avenue de la 
Médecine, Quebec City, Quebec, Canada G1V 0A6


Veterinary Microbiology, in press
 
Aeromonas salmonicida, a fish pathogen, is the causative agent of 
furunculosis. It was already shown that growing this bacterium in stressful 
conditions such as temperature above 22°C might lead to virulence 
attenuation. Unfortunately, many veterinary microbiology services and 
reference centers still routinely cultivate A. salmonicida at 25°C. Here we 
tested the presence of virulence factors by growth on specific medium as 
well as the integrity of the pAsa5 plasmid, which bears an important 
virulence factor, the type III secretion system (TTSS), by PCR analysis in 
twenty strains, most of which were grown at 25°C in their laboratory of 
origin. The analysis revealed that strains, which encountered the more 
stressful growth conditions displayed the most frequent absence of A-layer 
protein and secreted proteolytic activity. Moreover, many strains had lost 
parts of the pAsa5 plasmid in which the TTSS region was almost always 
affected. To confirm the effect of stressful growth conditions on the plasmid, 
three strains with an intact pAsa5 were cultured at 25°C for two weeks. A 
low but significant fraction of the tested colonies displayed pAsa5 
rearrangements. The rearrangement always affected the TTSS region and 
led to a loss of virulence in the Dictyostelium discoideum co-culture assay. 
These results demonstrate that the instability of pAsa5 did not lead to its 
complete loss as previously proposed but to a more complex rearrangement 
phenomenon and emphasizes the necessity to grow A. salmonicida in 
appropriate conditions to preserve the complete virulence of the bacterium.


Submitted by Steve Charette [[log in to unmask]]
==============================================================
[End dictyNews, volume 36, number 14]