dictyNews Electronic Edition Volume 38, number 23 September 14, 2012 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 ========= Amino acid repeats cause extraordinary coding sequence variation in the social amoeba Dictyostelium discoideum Clea Scala1 *, Xiangjun Tian2 *, Natasha J. Mehdiabadi1,3,, Margaret H. Smith1, Gerda Saxer4, Katie Stephens1, Prince Buzombo1, Joan E. Strassmann2, David C. Queller2 PLoS One, in press Protein sequences are normally the most conserved elements of genomes owing to purifying selection to maintain their functions. We document an extraordinary amount of within-species protein sequence variation in the model eukaryote Dictyostelium discoideum stemming from triplet DNA repeats coding for long strings of single amino acids. D. discoideum has a very large number of such strings, many of which are polyglutamine repeats, the same sequence that causes various human neurological disorders in humans, like HuntingtonÕs disease. We show here that D. discoideum coding repeat loci are highly variable among individuals, making D. discoideum a candidate for the most variable proteome. The coding repeat loci are not significantly less variable than similar non-coding triplet repeats. This pattern is consistent with these amino-acid repeats being largely non-functional sequences evolving primarily by mutation and drift. Submitted by David Queller [queller@wustl.edu] --------------------------------------------------------------------------- Mitochondrial fission and fusion in Dictyostelium discoideum: a search for proteins involved in membrane dynamics Brixey G Schimmel, Gregory W Berbusse, and Kari Naylor BMC Research Notes, in press Background Mitochondrial morphology is maintained by two distinct membrane events -fission and fusion. Altering these conserved processes can disrupt mitochondrial morphology and distribution, thereby disrupting the organelleÕs functionality and impeding cellular function. In higher eukaryotes, these processes are mediated by a family of dynamin-related proteins (DRPÕs). In the lower eukaryotes, for instance Dictyostelium discoideum, mitochondrial fission and fusion have been implicated but not yet established. To understand the overall mechanism of these dynamics across organisms, we developed an assay to identify fission and fusion events in Dictyostelium and to assess the involvement of the mitochondrial proteins, MidA, CluA, and two DRPÕs, DymA and DymB. Findings Using laser scanning confocal microscopy we show, for the first t ime, that lower eukaryotes mediate mitochondrial fission and fusion. In Dictyostelium, these processes are balanced, occurring approximately 1 event/minute. Quantification of the rates in midA-, cluA-, dymA-, or dymB- strains established that MidA appears to play an indirect role in the regulation of fission and fusion, while the DRPÕs are not essential for these processes. Rates of fission and fusion were significantly reduced in cluA-cells, indicating that CluA is necessary for maintaining both fission and fusion. Conclusions We have successfully demonstrated that Dictyostelium mitochondria undergo the dynamic processes of fission and fusion. The classical mediators of membrane dynamics - the DRPÕs Š are not necessary for these dynamics, whereas CluA is necessary for both processes. This work contributes to our overall understanding of mitochondrial dynamics and ultimately will provide additional insight into mitochondrial disease. Submitted by Kari Naylor [kknaylor@uca.edu] ============================================================== [End dictyNews, volume 38, number 23]