dictyNews Electronic Edition Volume 39, number 34 December 6, 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 ========= The Dictyostelium discoideum RNA-dependent RNA Polymerase RrpC Silences the Centromeric Retrotransposon DIRS-1 Post-transcriptionally and is Required for the Spreading of RNA Silencing Signals Stephan Wiegand, Doreen Meier, Carsten Seehafer, Marek Malicki, Patrick Hofmann, Anika Schmith, Thomas Winckler, Balint Foeldesi, Benjamin Boesler, Wolfgang Nellen, Johan Reimegard, Max Kaeller, Jimmie Haellman, Olof Emanuelsson, Lotta Avesson, Fredrik Soederbom and Christian Hammann Nucleic Acids Research, in press DIRS-1 is the founding member of a poorly characterized class of retrotransposable elements that contain inverse long terminal repeats and tyrosine recombinase instead of DDE-type integrase enzymes. In Dictyostelium discoideum, DIRS-1 forms clusters that adopt the function of centromeres, rendering tight retrotransposition control critical to maintaining chromosome integrity. We report that in deletion strains of the RNA-dependent RNA polymerase RrpC, full length and shorter DIRS-1 mRNAs are strongly enriched. Shorter versions of a hitherto unknown long non-coding RNA in DIRS-1 antisense orientation are also enriched in rrpC- strains. Concurrent with the accumulation of long transcripts, the vast majority of small (21mer) DIRS-1 RNAs vanish in rrpC- strains. RNASeq reveals an asymmetric distribution of the DIRS-1 small RNAs, both along DIRS-1 and with respect to sense and antisense orientation. We show that RrpC is required for post-transcriptional DIRS-1 silencing, and also for the spreading of RNA silencing signals. Finally, DIRS-1 mis-regulation in the absence of RrpC leads to retrotransposon mobilization. In summary, our data reveals RrpC as a key player in the silencing of centromeric retrotransposon DIRS-1. RrpC acts at the post-transcriptional level and is involved in the spreading of RNA silencing signals, both in the 5Õ and 3Õ directions. Submitted by Christian Hammann [c.hammann@jacobs-university.de] --------------------------------------------------------------------------- A CRIB domain mediates functions of coronin Karthic Swaminathan, Annette Mueller-Taubenberger, Jan Faix, Francisco Rivero, Angelika A. Noegel PNAS, in press The CRIB (Cdc42- and Rac-interactive binding) motif of coronin binds to Rho GTPases with a preference for GDP-loaded Rac. Mutation of the CRIB motif abrogates Rac binding. This results in increased 1evels of activated Rac in coronin deficient Dictyostelium cells (corA-), which impacts myosin II assembly. corA- cells show increased accumulation of myosin II in the cortex of growth-phase cells. Myosin II assembly is regulated by myosin heavy chain kinase (MHCK)-mediated phosphorylation of its tail. Kinase activity depends on the activation state of the p21-activated kinase PAKa. The myosin II defect of corA- mutant is alleviated by dominant negative PAKa. It is rescued by wild type coronin whereas coronin carrying a mutated CRIB failed to rescue the myosin defect in corA- mutant cells. Ectopically expressed MHCKs affinity-purified from corA- cells show reduced kinase activity. We propose that coronin through its affinity for GDP-Rac regulates the availability of GTP-Rac for activation of downstream effectors. Submitted by Angelika Noegel [noegel@uni-koeln.de] ============================================================== [End dictyNews, volume 39, number 34]