dictyNews Electronic Edition Volume 43, number 3 February 3, 2017 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 ========= In Memoriam: Maurice Sussman (1922–2016) Steve Alexander, Jakob Franke, Herb Ennis, Hannah Alexander Developmental Biology: http://www.sciencedirect.com/science/article/pii/S0012160616305978 submitted by: Steve Alexander [AlexanderSt@missouri.edu] ——————————————————————————————————————— Effects of deletion of the receptor CrlA on Dictyostelium aggregation and MPBD mediated responses are strain-dependent and not evident in strain Ax2 Takaaki B. Narita*, Pauline Schaap, Tamao Saito FEMS Microbiology Letters, in press The polyketide MPBD (4-methyl-5-pentylbenzene-1, 3-diol) is produced by the polyketide synthase SteelyA (StlA) in Dictyostelium discoideum. MPBD is required for appropriate expression of cAMP signalling genes involved in cell aggregation and additionally induces the spore maturation at the fruiting body stage. The MPBD signalling pathway for regulation of cell aggregation is unknown, but MPBD effects on sporulation were reported to be mediated by the G-protein coupled receptor CrlA in D. discoideum KAx3. In this study, we deleted the crlA gene from the same parental strain (Ax2) that was used to generate the MPBD-less mutant. We found that unlike the MPBD-less mutant, Ax2-derived crlA- mutants exhibited normal cell aggregation, indicating that in Ax2 MPBD effects on early development do not require CrlA. We also found that the Ax2/crlA- mutant formed normal spores in fruiting bodies. When transformed with PkaC, both Ax2 and Ax2/crlA- similarly responded to MPBD in vitro with spore encapsulation. Our data make it doubtful that CrlA acts as the receptor for MPBD signalling during the development of D. discoideum Ax2. submitted by: Takaaki Narita [b.narita@dundee.ac.uk] ——————————————————————————————————————— Coupled Excitable Ras and F-actin activation mediate spontaneous pseudopod formation and directed cell movement. Peter J.M. van Haastert, Ineke Keizer-Gunnink and Arjan Kortholt Department of Cell Biochemistry, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands. Molecular Biology of the Cell, in press Many eukaryotic cells regulate their mobility by external cues. Genetic studies have identified more than hundred components that participate in chemotaxis, which hinders to identify the conceptual framework how cells sense and respond to shallow chemical gradients. The activation of Ras occurs during basal locomotion, and is an essential connector between receptor and the cytoskeleton during chemotaxis. Using a sensitive assay for activated Ras we show here that activation of Ras and F-actin form two excitable systems that are coupled through mutual positive feedback and memory. This coupled excitable system leads to short-lived patches of activated Ras and associated F-actin that precede the extension of protrusions. In buffer excitability starts frequently with Ras activation in the back/side of the cell or with F-actin in the front of the cell. In a shallow gradient of chemoattractant local Ras activation triggers full excitation of Ras and subsequently F-actin at the side of the cell facing the chemoattractant , leading to directed pseudopod extension and chemotaxis. A computational model shows that the coupled excitable Ras/F-actin system forms the driving heart for the ordered-stochastic extension of pseudopods in buffer and for efficient directional extension of pseudopods in chemotactic gradients. submitted by: Peter van Haastert [p.j.m.van.haastert@rug.nl] ============================================================== [End dictyNews, volume 43, number 3]