dictyNews Electronic Edition Volume 29, number 11 October 12, 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 ========= Isoprenylcysteine carboxyl methylation is essential for development in Dictyostelium discoideum Ying Chen*, Kyle J. McQuade*, Xiao-Juan Guan, Peter A. Thomason, Michael S. Wert, Jeffry B. Stock, Edward C. Cox** Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA *These authors contributed equally to this work. **To whom correspondence should be addressed (ecox@molbio.princeton.edu). Molecular Biology of the Cell, in press Members of the Ras superfamily of small GTPases and the heterotrimeric G protein γ subunit are methylated on their carboxy-terminal cysteine residues by isoprenylcysteine methyltransferase. In Dictyostelium discoideum, small GTPase methylation occurs seconds after stimulation of starving cells by cAMP and returns quickly to basal levels, suggesting an important role in cAMP-dependent signaling. Deleting the isoprenylcysteine methyltransferase-encoding gene causes dramatic defects. Starving mutant cells do not propagate cAMP waves in a sustained fashion and do not aggregate. Motility is rescued when cells are pulsed with exogenous cAMP, or co-plated with wild-type cells, but the rescued cells exhibit altered polarity. cAMP-pulsed methyltransferase-deficient cells that have aggregated fail to differentiate, but mutant cells plated in a wild-type background are able to do so. Localization of and signaling by RasG is altered in the mutant. Localization of the heterotrimeric Ggamma protein subunit was normal, but signaling was altered in mutant cells. These data indicate that isoprenylcysteine methylation is required for intercellular signaling and development in Dictyostelium. Submitted by: Ted Cox [ecox@molbio.princeton.edu] -------------------------------------------------------------------------------- An unusually low microsatellite mutation rate in Dictyostelium discoideum, an organism with unusually abundant microsatellites Ryan McConnell, Sara Middlemist, Clea Scala, Joan E. Strassmann, David C. Queller Dept. of Ecology and Evolutionary Biology, Rice University, Houston, Texas, USA Genetics, in press The genome of the social amoeba Dictyostelium discoideum is known to have a very high density of microsatellite repeats, including thousands of triplet microsatellite repeats in coding regions that apparently code for long runs of single amino acids. We used a mutation accumulation study to see if unusually high microsatellite mutation rates contribute to this pattern. There was a modest bias towards mutations that increase repeat number, but because upward mutations were smaller than downward ones, this did not lead to a net average increase in size. Longer microsatellites had higher mutation rates than shorter ones, but did not show greater directional bias. The most striking finding is that the overall mutation rate is the lowest reported for microsatellites, about 1 x 10-6 for 10 dinucleotide loci and 6 x 10-6 for 52 trinucleotide loci (which were longer). High microsatellite mutation rates therefore do not explain the high incidence of microsatellites. The causal relation may in fact be reversed, with low mutation rates evolving to protect against deleterious fitness effects of mutation at the numerous microsatellites. Submitted by: Dave Queller [queller@rice.edu] ============================================================== [End dictyNews, volume 29, number 11]