dictyNews Electronic Edition Volume 35, number 3 July 16, 2010 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 ========= Abstracts ========= A fully resolved phylogeny of the social amoebas (Dictyostelia) based on combined ncSSU and ITS rDNA Sequences Romeralo, M. Spiegel, F.W. & Baldauf, S. Protist (online 2010) The dictyostelids possess a complex life cycle including aggregative and multicellular stages. They also include one of the most widely studied protistan model organisms, Dictyostelium discoideum. The current molecular phylogeny of dictyostelids is based largely on SSU(18S) rDNA sequences and shows a deep taxon consisting of four major groups, none of which correspond to the three traditional morphologically-defined genera. However, due to the generally slowly evolving nature of SSUrDNA, these data fail to resolve the majority of branches within the four groups. Given the highly morphologically mixed nature of the dictyostelid groups, it is important to resolve relationships within them. We have determined sequences for the internal transcribed spacers (ITS) of rDNA for nearly all species in the original dictyostelid global phylogeny. Phylogenetic analyses of these data, in combination with the previously determined SSUrDNA sequences, confidently resolve nearly all branches in the tree. This now fully resolved phylogeny confirms the utility of ITS for dictyostelid systematics and lays the ground work for further evolutionary study of the group. Submitted by Maria Romeralo [maria.romeralo@gmail.com] -------------------------------------------------------------------------------- Dynamics of a novel centromeric histone variant CenH3 reveals the evolutionary ancestral timing of centromere biogenesis Manu Dubin*, Jörg Fuchs†, Ralph Gräf‡, Ingo Schubert†, Wolfgang Nellen*,§. *Department of Genetics, University Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany †Leibniz-Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466 Gatersleben, Germany ‡Department of Cell Biology, Institute for Biochemistry and Biology, University of Potsdam, Potsdam-Golm, Germany. Nucleic Acids Res., in press The centromeric histone H3 variant (CenH3) serves to target the kinetochore to the centromeres and thus ensures correct chromosome segregation during mitosis and meiosis. The Dictyostelium H3-like variant H3v1 was identified as the CenH3 ortholog. Dictyostelium CenH3 has an extended N-terminal domain with no similarity to any other known proteins and a histone fold domain at its C-terminus. Within the histone fold, alpha-helix 2 (alpha2) and an extended loop 1 (L1) have been shown to be required for targeting CenH3 to centromeres. Compared to other known and putative CenH3 histones, Dictyostelium CenH3 has a shorter L1 suggesting that the extension is not an obligatory feature. Through ChIP analysis and fluorescence microscopy of live and fixed cells we provide here the first survey of centromere structure in amoebozoa. The six telocentric centromeres were found to mostly consist of all the DIRS-1 elements and to associate with H3K9me3. During interphase the centromeres remain attached to the centrosome forming a single CenH3 containing cluster. Loading of Dictyostelium CenH3 onto centromeres occurs at the G2/prophase transition, in contrast to the anaphase/telophase loading of CenH3 observed in metazoans. This suggests that loading during G2/prophase is the ancestral eukaryotic mechanism and that anaphase/telophase loading of CenH3 has evolved more recently after the amoebozoa diverged from the animal linage. Submitted by Wolfgang Nellen [nellen@uni-kassel.de] ============================================================== [End dictyNews, volume 35, number 3]