Dicty News Electronic Edition Volume 25, number 1 July 8, 2005 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 Dicty-News, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ============= Abstracts ============= The Dictyostelium Genome Encodes Numerous RasGEFs with Multiple Biological Roles Andrew Wilkins2*, Karol Szafranski1*, Derek J. Fraser3, Deenadayalan Bakthavatsalam4, Rolf Mueller4, Paul R. Fisher3, Gernot Gloeckner1, Ludwig Eichinger4, Angelika Noegel4 and Robert H. Insall2,5 1 Genome Analysis, Institute for Molecular Biotechnology, Beutenbergstr. 11, D-07745 Jena, Germany 2 School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK 3 La Trobe University, VIC 3086, Australia 4 Centre for Biochemistry and Centre for Molecular Medicine Cologne, Medical Faculty, University of Cologne, Joseph-Stelzmann-Str. 52, 50931 Cologne, Germany 5 Corresponding author BACKGROUND Dictyostelium discoideum is a eukaryote with a simple lifestyle and a relatively small genome whose sequence has been fully determined. It is widely used for studies on cell signalling, movement and multicellular development. Ras nucleotide exchange factors (RasGEFs) are the proteins which activate Ras and thus lie near the top of multiple signalling pathways. They are particularly important for signalling in development and chemotaxis in many organisms including Dictyostelium. RESULTS We have searched the genome for sequences encoding RasGEFs. Despite its relative simplicity, we find that the Dictyostelium genome encodes at least 25 RasGEFs, with a few other genes encoding only parts of the RasGEF consensus domains. All appear to be expressed at some point in development. The 25 genes include a wide variety of domain structures, most of which have not been seen in other organisms. The LisH domain, which is associated with microtubule binding, is seen particularly frequently; other domains which confer interactions with the cytoskeleton are also common. Disruption of a sample of the novel genes reveals that many have clear phenotypes, including altered morphology and defects in chemotaxis, slug phototaxis and thermotaxis. CONCLUSIONS These results suggest that the unexpectedly large number of RasGEF genes reflects an evolutionary expansion of the range of Ras signalling rather than functional redundancy or the presence of multiple pseudogenes. Submitted by: Robert Insall [r.h.insall@bham.ac.uk] ----------------------------------------------------------------------------- Dictyopyrones, novel a-pyronoids isolated from Dictyostelium spp., promote stalk cell differentiation in Dictyostelium discoideum Akiko Arai, Yukino Goto, Aiko Hasegawa, Kohei Hosaka, Haruhisa Kikuchi, Yoshiteru Oshima, Susumu Tanaka and Yuzuru Kubohara* *Gunma University IMCR, Maebshi 371-8512, Japan Differentiation, in press Dictyopyrones A and B (DpnA and DpnB) whose function(s) is not known were isolated from fruiting bodies of Dictyostelium discoideum. In the present study, to assess their function(s), we examined the effects of Dpns on in vitro cell differentiation in D. discoideum monolayer cultures with cAMP. Dpns at 1-20 microM promoted stalk cell formation to some extent in the wild-type strain V12M2. Although Dpns by themselves could hardly induce stalk cell formation in a DIF-deficient strain HM44, both of them dose-dependently promoted DIF-1-dependent stalk cell formation in the strain. In the sporogenous strain HM18, Dpns at 1-20 microM suppressed spore formation and promoted stalk cell formation in a dose-dependent manner. Analogs of Dpns were less effective in affecting cell differentiation in both HM44 and HM18 cells, indicating that the activity of Dpns should be chemical structure-specific. It was also shown that DpnA at 2-20 microM dose-dependently suppressed spore formation induced with 8-bromo cAMP and promoted stalk cell formation in V12M2 cells. Interestingly, it was shown by the use of RT-PCR that DpnA at 10 microM slightly promoted both prespore- and prestalk-specific gene expressions in an early phase of V12M2 and HM18 in vitro differentiation. The present results suggest that Dpns may have functions 1) to promote both prespore and prestalk cell differentiation in an early stage of development and 2) to suppress spore formation and promote stalk cell formation in a later stage of development in D. discoideum. Submitted by: Yuzuru Kubohara