dictyNews Electronic Edition Volume 39, number 33 November 29, 2013 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 dictyBase has a job opening! http://dictybase.org/dictybase_jobs.html ========= Abstracts ========= Interspecies and intraspecies interactions in social amoebae Santosh Sathe, Neha Khetan and Vidyanand Nanjundiah Centre for Ecological Sciences and Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore- 560012, India. Corresponding author: Santosh Sathe (santosh_sathe@ces.iisc.ernet.in) Journal of Evolutionary Biology, in press The stable coexistence of individuals of different genotypes and reproductive division of labour within heterogeneous groups are of fundamental interest from the viewpoint of evolution. Cellular slime moulds are convenient organisms in which to address both issues. Strains of a species co-occur, and so do different species. As a result social groups in the wild are often genetically heterogeneous. Generally, amoebae of strains that participate in genetically mixed groups differ in the efficiency with which they form spores, which raises questions regarding the basis of their long-term coexistence. We have carried out intra- and inter-species 1:1 pair wise mixes between wild isolates of Dictyostelium giganteum and D. purpureum. Mixing leads to co-aggregation, after which the constituents of the chimaeric aggregate sort out to varying extents. On the whole, intra-species aggregates tend to develop in concert and give rise to chimaeric fruiting bodies in which there are disproportionately more spores of one component than the other. Inter- species aggregates exhibit almost complete sorting out and most if not all spores in a fruiting body belong to a single species. Somatic compatibility is assessed by successful participation in forming a chimaeric fruiting body. It is highest within clones, lower among strains of the same species and lowest between strains of different species. Further, somatic compatibility is negatively correlated with the variance in the proportions of spores contributed by either component in the mix. The long-term coexistence of cellular slime moulds would appear to involve tradeoffs between fitness-related traits (when strains that co-aggregate belong to the same species and are compatible, and constitute what we term a guild), sorting out (when the strains belong to different guilds in the same species and are incompatible) and avoidance (when strains belong to different species). We speculate that incompatible guilds of the same species represent an early step in the splitting of one species into two. Submitted by Santosh Sathe [santosh_sathe@ces.iisc.ernet.in] --------------------------------------------------------------------------- The arrestin-domain containing protein AdcA is a response element to stress Habourdin C, Klein G, Araki T, Williams JG, Aubry L. Cell Communication and Signaling, in press BACKGROUND: Cell behaviour is tightly determined by sensing and integration of extracellular changes through membrane detectors such as receptors and transporters and activation of downstream signalling cascades. Arrestin proteins act as scaffolds at the plasma membrane and along the endocytic pathway, where they regulate the activity and the fate of some of these detectors. Members of the arrestin clan are widely present from unicellular to metazoa, with roles in signal transduction and metabolism. As a soil amoeba, Dictyostelium is frequently confronted with environmental changes likely to compromise survival. Here, we investigated whether the recently described arrestin-related protein AdcA is part of the cell response to stresses. RESULTS: Our data provide evidence that AdcA responds to a variety of stresses including hyperosmolarity by a transient phosphorylation. Analysis in different mutant backgrounds revealed that AdcA phosphorylation involves pathways other than the DokA and cGMP-dependent osmostress pathways, respectively known to regulate PKA and STATc, key actors in the cellular response to conditions of hyperosmolarity. Interestingly, however, both AdcA and STATc are sensitive to changes in the F-actin polymerization status, suggesting a common primary sensor/trigger and linking the stress-sensitive kinase responsive for AdcA phosphorylation to the actin cytoskeleton. We also show that STATc-dependent transcriptional activity is involved for the timely dephosphorylation of AdcA in cells under stress. CONCLUSION: Under osmotic stress, AdcA undergoes a phosphorylation- dephosphorylation cycle involving a stress-sensitive kinase and the transcription regulator STATc. This transient post-transcriptional modification may allow a regulation of AdcA function possibly to optimize the cellular stress response. Submitted by Laurence Aubry [laubry@cea.fr] --------------------------------------------------------------------------- Developmental lineage priming in Dictyostelium by heterogeneous Ras activation Alex Chattwood1,¤, Koki Nagayama1,¤, Parvin Bolourani2, Lauren Harkin1, Marzieh Kamjoo1, Gerald Weeks2 and Christopher R.L. Thompson1* 1 Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Rd, Manchester, M13 9PT 2 Department of Microbiology and Immunology, University of British Columbia, Life Sciences Centre, 2350 Health Sciences Mall, Vancouver BC, V6T 1Z3, Canada * Corresponding author ¤ These authors contributed equally eLife, in press In cell culture, genetically identical cells often exhibit heterogeneous behavior, with only Ôlineage primedÕ cells responding to differentiation inducing signals. It has recently been proposed that such heterogeneity exists during normal embryonic development to allow position independent patterning based on Ôsalt and pepperÕ differentiation and sorting out. However, the molecular basis of lineage priming and how it leads to reproducible cell type proportioning is poorly understood. To address this, we employed a novel forward genetic approach in the model organism Dictyostelium discoideum. These studies revealed the Ras-GTPase regulator, gefE, to be required for normal lineage priming and salt and pepper differentiation. We find that this is because Ras-GTPase activity sets the intrinsic response threshold to lineage specific differentiation signals. Importantly, we show that although gefE expression is uniform, transcription of its target, rasD, is both heterogeneous and dynamic, thus providing a novel mechanism for heterogeneity generation and position independent differentiation. Submitted by Chris Thompson [christopher.thompson@manchester.ac.uk] ============================================================== [End dictyNews, volume 39, number 33]