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 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. 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 [wloomis@ucsd.edu] -------------------------------------------------------------------------------- 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 [vidya@ces.iisc.ernet.in] -------------------------------------------------------------------------------- Alteration of virulence factors and rearrangement of pAsa5 plasmid caused by the growth of Aeromonas salmonicida in stressful conditions Rana K. Daher1,2, Genevieve Filion1,2, Sok Gheck E. Tan2, Stephanie Dallaire-Dufresne1,2, Valerie E. Paquet1,2 and Steve J. Charette1,2,3* 1. Institut de biologie integrative et des systemes, Pavillon Charles-Eugene- Marchand, Universite Laval, 1030 avenue de la Medecine, Quebec City, Quebec, Canada, G1V 0A6 2. Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Quebec (Hopital Laval), 2725 Chemin Sainte-Foy, Quebec City, Quebec, Canada, G1V 4G5 3. Departement de biochimie, de microbiologie et de bio-informatique, Faculte des sciences et de genie, Universite Laval, 1045 avenue de la Medecine, 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 [Steve.Charette@bcm.ulaval.ca] ============================================================== [End dictyNews, volume 36, number 14]