dictyNews Electronic Edition Volume 41, number 18 August 28, 2015 Please submit abstracts of your papers as soon as they have been accepted for publication 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 ========= A host factor supports retrotransposition of the TRE5-A population in Dictyostelium cells by suppressing an Argonaute protein Anika Schmith1, Thomas Spaller1, Friedemann Gaube1, sa Fransson2, Benjamin Boesler3, Sandeep Ojha4, Wolfgang Nellen3, Christian Hammann4, Fredrik Sšderbom5, Thomas Winckler1 1 Department of Pharmaceutical Biology, Institute of Pharmacy, University of Jena, Germany 2 Department of Molecular Biology, Biomedical Center, Swedish University of Agricultural Sciences, Uppsala, Sweden 3 Institute of Biology Š Genetics, University of Kassel, Germany 4 Ribogenetics@Biochemistry Lab, Department of Life Sciences and Chemistry, Molecular Life Sciences Research Center, Jacobs University Bremen, Germany 5 Department of Cell and Molecular Biology, Biomedical Center, Uppsala University, Sweden Mobile DNA, in press Background: In the compact and haploid genome of Dictyostelium discoideum control of transposon activity is of particular importance to maintain viability. The non-long terminal repeat retrotransposon TRE5-A amplifies continuously in D. discoideum cells even though it produces considerable amounts of minus-strand (antisense) RNA in the presence of an active RNA interference machinery. Removal of the host-encoded C-module-binding factor (CbfA) from D. discoideum cells resulted in a more than 90% reduction of both plus- and minus-strand RNA of TRE5-A and a strong decrease of the retrotransposition activity of the cellular TRE5-A population. Transcriptome analysis revealed an approximately 230-fold overexpression of the gene coding for the Argonaute-like protein AgnC in a CbfA-depleted mutant. Results: The D. discoideum genome contains orthologs of RNA- dependent RNA polymerases, Dicer-like proteins, and Argonaute proteins that are supposed to represent RNA interference pathways. We analyzed available mutants in these genes for altered expression of TRE5-A. We found that the retrotransposon was overexpressed in mutants lacking the Argonaute proteins AgnC and AgnE. Because the agnC gene is barely expressed in wild-type cells, probably due to repression by CbfA, we employed a new method of promoter-swapping to overexpress agnC in a CbfA-independent manner. In these strains we established an in vivo retrotransposition assay that determines the retrotransposition frequency of the cellular TRE5-A population. We observed that both the TRE5-A steady-state RNA level and retrotransposition rate dropped to less than 10% of wild-type in the agnC overexpressor strains. Conclusions: The data suggest that TRE5-A amplification is controlled by a distinct pathway of the Dictyostelium RNA interference machinery that does not require RNA-dependent RNA polymerases but involves AgnC. This control is at least partially overcome by the activity of CbfA, a factor derived from the retrotransposon's host. This unusual regulation of mobile element activity most likely had a profound effect on genome evolution in D. discoideum. Submitted by Thomas Winckler [t.winckler@uni-jena.de] ---------------------------------------------------------------------- Organization of microtubule assemblies in Dictyostelium syncytia depends on the microtubule crosslinker, Ase1 Irina Tikhonenko, Karen Irizarry, Alexey Khodjakov, and Michael P. Koonce Division of Translational Medicine Wadsworth Center NYS Department of Health Albany, NY 12201-0509 Cell Molecular Life Sciences, in press It has long been known that the interphase microtubule (MT) array is a key cellular scaffold that provides structural support and directs organelle trafficking in eukaryotic cells. Although in animal cells, a combination of centrosome nucleating properties and polymer dynamics at the distal microtubule ends is generally sufficient to establish a radial, polar array of MTs, little is known about how effector proteins (motors and crosslinkers) are coordinated to produce the diversity of interphase MT array morphologies found in nature. This diversity is particularly important in multinucleated environments where multiple MT arrays must coexist and function. We initiate here a study to address the higher ordered coordination of multiple, independent MT arrays in a common cytoplasm. Deletion of a MT crosslinker of the MAP65/Ase1/PRC1 family disrupts the spatial integrity of multiple arrays in Dictyostelium discoideum, reducing the distance between centrosomes and increasing the intermingling of MTs with opposite polarity. This result, coupled with previous dynein disruptions suggest a robust mechanism by which interphase MT arrays can utilize motors and crosslinkers to sense their position and minimize overlap in a common cytoplasm. Submitted by Mike Koonce [michael.koonce@health.ny.gov] ============================================================== [End dictyNews, volume 41, number 18]