dictyNews Electronic Edition Volume 28, number 12 May 11, 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 ========= G Protein-Independent Ras/PI3K/F-Actin Circuit Regulates Basic Cell Motility Atsuo T. Sasaki, Chris Janetopoulos, Susan Lee, Pascale G. Charest, Kosuke Takeda, Lauren W. Sundheimer, Ruedi Meili, Peter N. Devreotes and Richard A. Firtel J. Cell Biology PI3Kgamma and Dictyostelium PI3K are activated via G-protein coupled receptors through binding to the Gbeta/gamma subunit and Ras. However, the mechanistic role(s) of Gbeta/gamma and Ras in PI3K activation remain elusive. Furthermore, the dynamics and function of PI3K activation in the absence of extracellular stimuli have not been fully investigated. We report that Gbeta null cells display PI3K and Ras activation, as well as the reciprocal localization of PI3K and PTEN, which lead to local accumulation of PI(3,4,5)P3. Simultaneous imaging analysis reveals that, in the absence of extracellular stimuli, autonomous PI3K and Ras activation occur, concurrently, at the same sites where F-actin projection emerges. The loss of PI3K binding to Ras-GTP abolishes this PI3K activation, while prevention of PI3K activity suppresses autonomous Ras activation, suggesting that PI3K and Ras form a positive-feedback circuit. This circuit is associated with both random cell migration and cytokinesis and may have initially evolved to control stochastic changes in the cytoskeleton. Submitted by: Rick Firtel [rafirtel@ucsd.edu] -------------------------------------------------------------------------------- STATc is a key regulator of the transcriptional response to hyperosmotic shock Jianbo Na, Budi Tunggal and Ludwig Eichinger Institute for Biochemistry I, Medical Faculty, University of Cologne, Joseph-Stelzmann-Strasse 52, 50931 Cologne, Germany BMC Genomics, in press Dictyostelium discoideum is frequently subjected to environmental changes in its natural habitat, the forest soil. In order to survive, the organism had to develop effective mechanisms to sense and respond to such changes. When cells are faced with a hypertonic environment a complex response is triggered. It starts with signal sensing and transduction and leads to changes in cell shape, the cytoskeleton, transport processes, metabolism and gene expression. Certain aspects of the Dictyostelium osmotic stress response have been elucidated, however, no comprehensive picture was available up to now. To better understand the D. discoideum response to hyperosmotic conditions, we performed gene expression profiling using DNA microarrays. The transcriptional profile of cells treated with 200 mM sorbitol during a 2-hour time course revealed a time-dependent induction or repression of 809 genes, more than 15% of the genes on the array, which peaked 45 to 60 minutes after the hyperosmotic shock. The differentially regulated genes were applied to cluster analysis and functional annotation using gene ontology (GO) terms. Two main responses appear to be the down-regulation of the metabolic machinery and the up-regulation of the stress response system, including STATc. Further analysis of STATc revealed that it is a key regulator of the transcriptional response to hyperosmotic shock. Approximately 20% of the differentially regulated genes were dependent on the presence of STATc. At least two signalling pathways are activated in Dictyostelium cellssubjected to hypertonicity. STATc is responsible for the transcriptional changes of one of them. Submitted by: Ludwig Eichinger [ludwig.eichinger@uni-koeln.de] ============================================================== [End dictyNews, volume 28, number 12]