Dicty News Electronic Edition Volume 25, number 2 July 29, 2005 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 Dicty-News, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ============= Abstracts ============= TOR Complex 2 Integrates Cell Movement during Chemotaxis and Signal Relay in Dictyostelium Susan Lee1, Frank I. Comer, Atsuo Sasaki, Ian X. McLeod, Yung Duong, Koichi Okumura, John R. Yates III, Carole A. Parent, and Richard A. Firtel Mol. Cell. Bio. in press Dictyostelium cells form a multicellular organism through the aggregation of independent cells. This process requires both chemotaxis and signal relay in which the chemoattractant cAMP activates adenylyl cyclase through the G protein-coupled cAMP receptor cAR1. cAMP is produced and secreted and it activates receptors on neighboring cells, thereby relaying the chemoattractant signal to distant cells. Using co-immunoprecipitation and mass spectrometric analyses, we have identified a TOR-containing complex in Dictyostelium that is related to the TORC2 complex of S. cerevisiae and regulates both chemotaxis and signal relay. We demonstrate that mutations in Dictyostelium LST8, RIP3, and Pia, orthologs of the yeast TORC2 components LST8, AVO1, and AVO3, exhibit a common set of phenotypes including reduced cell polarity, chemotaxis speed and directionality, phosphorylation of Akt/PKB and the related PKBR1, and activation of adenylyl cyclase. Further, we provide evidence for a role of Ras in the regulation of TORC2. We propose that, through the regulation of chemotaxis and signal relay, TORC2 plays an essential role in controlling aggregation by coordinating the two essential arms of the developmental pathway that leads to multicellularity in Dictyostelium. Submitted by: Rick Firtel [rafirtel@ucsd.edu] ----------------------------------------------------------------------------- Direct mechanical force measurements during the migration of Dictyostelium slugs using flexible substrata Jean-Paul Rieu 1*, Catherine Barentin 1, Yasuo Maeda 2 and Yasuji Sawada 3 1 Laboratoire de Physique de la Matiere Condensee et Nanostructures,Universite Claude Bernard Lyon I & CNRS, 43 Boulevard du 11 Novembre, 69622 Villeurbanne Cedex, France; 2 Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan; 3 Tohoku Institute of Technology, 35-1 Yagiyama-Kasumi, Taihaku, 983, Sendai, Japan. Biophysical Journal, in press We use the flexible substrate method to study how and where are exerted mechanical forces during the migration of Dictyostelium slugs. This old and contentious issue has been left poorly understood so far. We are able to identify clearly separate friction forces in the tip and in the tail of the slug, traction forces mostly localized in the inner slug/surface contact area in the prespore region and large perpendicular forces directed in the outward direction at the outline of contact area. Surprisingly, the magnitude of friction and traction forces is decreasing with slug velocity indicating that these quantities are probably related to the dynamics of cell/substrate adhesion complexes. Contrary to what is always assumed in models and simulations, friction is not of fluid type (viscous drag) but rather close to solid friction. We suggest that the slime sheath confining laterally the cell mass of the slug experiences a tension that in turn is pulling out the elastic substrate in the direction tangential to the slug profile where sheath is anchored. In addition, we show in the appendix that the iterative method we developed is well adapted to study forces over large and continuous fields when the experimental error is sufficiently low and when the plane of recorded bead deformations is close enough to the elastomer surface, requirements fulfilled in this experimental study of Dictyostelium slugs. Submitted by: Yasuo Maeda [ymaeda@mail.tains.tohoku.ac.jp] ============================================================================== [End Dicty News, volume 25, number 2]