dictyNews Electronic Edition Volume 37, number 8 September 30, 2011 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 ========= Dictyostelium Chemotaxis: Essential Ras activation and accessory signaling pathways for amplification Arjan Kortholt, Rama Kataria, Ineke Keizer-Gunnink, Wouter N. Van Egmond, Ankita Khanna and Peter J.M. Van Haastert Department of Cell Biochemistry, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands EMBO reports, in press Central to chemotaxis is the molecular mechanism by which cells exhibit directed movement in shallow gradients of chemoattractant. We used Dictyostelium mutants to investigate the minimal requirements for chemotaxis, and identified a basal signaling module providing activation of Ras at the leading edge, which is sufficient for chemotaxis. The signaling enzymes PI3K, TorC2, PLA2 and sGC are not required for Ras activation and chemotaxis to folate or to steep gradients of cAMP, but they provide a memory of direction and improved orientation of the cell, which together increases the sensitivity ~150-fold for chemotaxis in shallow cAMP gradients. Submitted by: Peter van Haastert [p.j.m.van.haastert@rug.nl] -------------------------------------------------------------------------------- Stretching actin filaments within cells enhances their affinity for the myosin ii motor domain. Taro Q.P. Uyeda1,2, Yoshiaki Iwadate3, 4, Nobuhisa Umeki1, Akira Nagasaki1 and Shigehiko Yumura3 1: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan 2: Biomedicinal Information Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Koto, Tokyo, Japan 3: Department of Functional Molecular Biology, Graduate School of Medicine, Yamaguchi University, Yamaguchi, Yamaguchi, Japan 4: Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), Kawaguchi, Saitama, Japan PLoS One, in press To test the hypothesis that the myosin II motor domain (S1) preferentially binds to specific subsets of actin filaments in vivo, we expressed GFP-fused S1 with mutations that enhanced its affinity for actin in Dictyostelium cells. Consistent with the hypothesis, the GFP-S1 mutants were localized along specific portions of the cell cortex. Comparison with rhodamine-phalloidin staining in fixed cells demonstrated that the GFP-S1 probes preferentially bound to actin filaments in the rear cortex and cleavage furrows, where actin filaments are stretched by interaction with endogenous myosin II filaments. The GFP-S1 probes were similarly enriched in the cortex stretched passively by traction forces in the absence of myosin II or by external forces using a microcapillary. The preferential binding of GFP-S1 mutants to stretched actin filaments did not depend on cortexillin I or PTEN, two proteins previously implicated in the recruitment of myosin II filaments to stretched cortex. These results suggested that it is the stretching of the actin filaments itself that increases their affinity for the myosin II motor domain. In contrast, the GFP-fused myosin I motor domain did not localize to stretched actin filaments, which suggests different preferences of the motor domains for different structures of actin filaments play a role in distinct intracellular localizations of myosin I and II. We propose a scheme in which the stretching of actin filaments, the preferential binding of myosin II filaments to stretched actin filaments, and myosin II-dependent contraction form a positive feedback loop that contributes to the stabilization of cell polarity and to the responsiveness of the cells to external mechanical stimuli. Submitted by: Taro Uyeda [t-uyeda@aist.go.jp] ============================================================== [End dictyNews, volume 37, number 8]