dictyNews Electronic Edition Volume 38, number 24 September 21, 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 ========= PIP3 waves and PTEN dynamics in the emergence of cell polarity Guenther Gerisch1*, Britta Schroth-Diez2, Annette Mueller-Taubenberger3, and Mary Ecke1 1Max Planck Institute of Biochemistry, 82152 Martinsried, Germany; 2Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany; and 3Ludwig Maximilian University of Munich, Institute for Cell Biology, 80336 Muenchen, Germany *Correspondence: gerisch@biochem.mpg.de Biophysical Journal, Volume 103, September 2012 1-9 In a motile eukaryotic cell, front protrusion and tail retraction are superimposed on each other. In order to single out mechanisms that result in front to tail or in tail to front transition, we separated the two processes in time using cells that oscillate between a "full front"and a "full tail" state. State transitions were visualized by total internal reflection fluorescence microscopy using as a front marker PIP3 (phosphatidyl inositol [3,4,5] tris-phosphate), and as a tail marker the tumor-suppressor PTEN (phosphatase tensin homologue) that degrades PIP3. Negative fluctuations in the PTEN layer of the membrane gated a local increase in PIP3. In a subset of areas lacking PTEN ("PTEN holes"), PIP3 was amplified until a propagated wave was initiated. Wave propagation implies that a PIP3 signal is transmitted by a self-sustained process, such that the temporal and spatial profiles of the signal are maintained during passage of the wave across the entire expanse of the cell membrane. Actin clusters were remodeled into a ring along the perimeter of the expanding PIP3 wave. The reverse transition of PIP3 to PTEN was linked to the previous site of wave initiation: where PIP3 decayed first, the entry of PTEN was primed. Submitted by Guenther Gerisch [gerisch@biochem.mpg.de] --------------------------------------------------------------------------- Whole Genome Sequencing of Mutation Accumulation Lines Reveals a Low Mutation Rate in the Social Amoeba Dictyostelium discoideum Gerda Saxer, Paul Havlak, Sara A. Fox, Michael A. Quance, Sharu Gupta, Yuriy Fofanov, Joan E. Strassmann, David C. Queller PLoS ONE, in press Spontaneous mutations play a central role in evolution. Despite their importance, mutation rates are some of the most elusive parameters to measure in evolutionary biology. The combination of mutation accumulation (MA) experiments and whole-genome sequencing now makes it possible to estimate mutation rates by directly observing new mutations at the molecular level across the whole genome. We performed an MA experiment with the social amoeba Dictyostelium discoideum and sequenced the genomes of three randomly chosen lines using high-throughput sequencing to estimate the spontaneous mutation rate in this model organism. The mitochondrial mutation rate of 6.76x10^-9, with a Poisson confidence interval of 4.1x10^-9 - 9.5x10^-9, per nucleotide per generation is slightly lower than estimates for other taxa. The mutation rate estimate for the nuclear DNA of 2.9x10^-11, with a Poisson confidence interval ranging from 7.4x10^-13 to 1.6x0^-10, is the lowest reported for any eukaryote. These results are consistent with low microsatellite mutation rates previously observed in D. discoideum and low levels of genetic variation observed in wild D. discoideum populations. In addition, D. discoideum has been shown to be quite resistant to DNA damage, which suggests an efficient DNA-repair mechanism that could be an adaptation to life in soil and frequent exposure to intracellular and extracellular mutagenic compounds. The social aspect of the life cycle of D. discoideum and a large portion of the genome under relaxed selection during vegetative growth could also select for a low mutation rate. This hypothesis is supported by a significantly lower mutation rate per cell division in multicellular eukaryotes compared with unicellular eukaryotes. Submitted by Gerda Saxer [gsaxer@rice.edu] ============================================================== [End dictyNews, volume 38, number 24]