dictyNews Electronic Edition Volume 29, number 7 Sptember 2, 2007 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. ========= Abstracts ========= The small RNA repertoire of Dictyostelium discoideum and its regulation by components of the RNAi pathway Andrea Hinas1,5, Johan Reimegård2, E. Gerhart H. Wagner2, Wolfgang Nellen3, Victor R. Ambros4, and Fredrik Söderbom1* 1Department of Molecular Biology, Biomedical Center, Swedish University of Agricultural Sciences, Box 590, SE-75124 Uppsala, Sweden 2Department of Cell and Molecular Biology, Biomedical Center, Uppsala University, Box 596, SE-75124 Uppsala, Sweden 3Department of Genetics, Kassel University, Heinrich Plett Strasse 40, 34132 Kassel, Germany 4Department of Genetics, Dartmouth Medical School, Hanover, NH 03755, USA 5Present address: Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Ave, Cambridge, MA 02138, USA *corresponding author Nucleic acids research, in press Small RNAs play crucial roles in regulation of gene expression in many eukaryotes. Here, we report the cloning and characterization of 18-26 nt RNAs in the social amoeba Dictyostelium discoideum. This survey uncovered developmentally regulated microRNA candidates whose biogenesis, at least in one case, is dependent on a Dicer homolog, DrnB. Furthermore, we identified a large number of 21 nt RNAs originating from the DIRS-1 retrotransposon, clusters of which have been suggested to constitute centromeres. Small RNAs from another retrotransposon, Skipper, were significantly up-regulated in strains depleted of the second Dicer-like protein, DrnA, and a putative RNA-dependent RNA polymerase, RrpC. In contrast, the expression of DIRS-1 small RNAs was not altered in any of the analyzed strains. This suggests the presence of multiple RNAi pathways in D. discoideum. In addition, we isolated several small RNAs with antisense complementarity to mRNAs. Three of these mRNAs are developmentally regulated. Interestingly, all three corresponding genes express longer antisense RNAs from which the small RNAs may originate. In at least one case, the longer antisense RNA is complementary to the spliced but not the unspliced pre-mRNA, indicating synthesis by an RNA-dependent RNA polymerase. Submitted by: Fredrik Söderbom [fredde@xray.bmc.uu.se] -------------------------------------------------------------------------------- Arachidonic acid is a chemoattractant for Dictyostelium discoideum cells. Ralph H. Schaloske, Dagmar Blaesius , Christina Schlatterer and Daniel F.Lusche J.Biosci., in press Cyclic AMP is the natural chemoattractant of the social amoebae Dictyostelium discoideum. It is detected by cell surface cAMP-receptors. Besides a signalling cascade involving phosphatidylinositol 3,4,5-trisphosphate (PIP3), Ca2+ signalling has been shown to have a major role in chemotaxis. Previously, we have shown that arachidonic acid (AA) induces an increase in the cytosolic Ca2+ concentration by releasing Ca2+ from intracellular stores and activating influx of extracellular Ca2+. Here we report that AA is a chemoattractant for D. discoideum cells differentiated for 8 to 9 hours. Motility towards a glass capillary filled with an AA solution was dose-dependent and qualitatively comparable to cAMP-induced chemotaxis. Ca2+ played an important role in AA chemotaxis of wild type Ax2 as ethyleneglycol-bis(b-aminoethyl)-N,N,N’,N’-tetraacetic acid (EGTA) added to the extracellular buffer strongly inhibited motility. In the HM1049 mutant whose iplA gene encoding a putative Ins(1,4,5)P3-receptor had been knocked out,chemotaxis was only slightly affected by EGTA. Chemotaxis in the presence of extracellular Ca2+ was similar in both strains. Unlike cAMP, addition of AA to a cell suspension did not change cAMP or cGMP levels. A model for AA chemotaxis based on the findings in this and previous work is presented. Submitted by: Daniel F.Lusche [daniel.lusche@web.de] ============================================================== [End dictyNews, volume 29, number 7]