dictyNews Electronic Edition Volume 33, number 7 September 11, 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. Follow dictyBase now on twitter: http://twitter.com/dictybase ========= Abstracts ========= Cheater-resistance is not futile Anupama Khare, Lorenzo Santorelli, Joan E. Strassmann, David C. Queller, Adam Kuspa and Gad Shaulsky Baylor College of Medicine and Rice University Nature, in press Cooperative social systems are susceptible to cheating by individuals that reap the benefits of cooperation without incurring the costs. There are various theoretical mechanisms for the repression of cheating and many have been tested experimentally. One possibility that has not been tested rigorously is the evolution of mutations that confer resistance to cheating. Here we show that the presence of a cheater in a population of randomly mutated social amoebae can select for cheater-resistance. Furthermore, we show that this cheater-resistance can be a noble strategy because the resistor strain does not necessarily exploit other strains. Thus, the evolution of resistors may be instrumental in preserving cooperative behavior in the face of cheating. Submitted by Gad Shaulsky [gadi@bcm.edu] -------------------------------------------------------------------------------- P180- mediated trafficking of Vamp7B limits homotypic fusion of Dictyostelium contractile vacuoles Yujia Wen, Irene Stavrou, Kirill Bersuker, Rebecca J. Brady, Arturo De Lozanne and Theresa J. O’Halloran Molecular, Cell & Dev Biology, University of Texas, Austin Molecular Biology of the Cell, in press Clathrin coated vesicles play an established role in endocytosis from the plasma membrane, but are also found on internal organelles. We examined the composition of clathrin coated vesicles on an internal organelle responsible for osmoregulation, the Dictyostelium discoideum contractile vacuole. Clathrin puncta on contractile vacuoles contained multiple accessory proteins typical of plasma membrane coated pits, including AP2, AP180, and epsin, but not Hip1r. To examine how these clathrin accessory proteins influenced the contractile vacuole, we generated cell lines that carried single and double gene knockouts in the same genetic background. Single or double mutants that lacked AP180 or AP2 exhibited abnormally large contractile vacuoles. The enlarged contractile vacuoles in AP180 null mutants formed because of excessive homotypic fusion among contractile vacuoles. The SNARE protein Vamp7B, was mislocalized and enriched on the contractile vacuoles of AP180 null mutants. In vitro assays revealed that AP180 interacted with the cytoplasmic domain of Vamp7B.  We propose that AP180 directs Vamp7B into clathrin coated vesicles on contractile vacuoles, creating an efficient mechanism for regulating the internal distribution of fusion-competent SNARE proteins and limiting homotypic fusions among contractile vacuoles.  Dictyostelium contractile vacuoles offer a valuable system to study clathrin coated vesicles on cell internal organelles. Submitted by Terry O'Halloran [t.ohalloran@mail.utexas.edu] ============================================================== [End dictyNews, volume 33, number 7]