dictyNews Electronic Edition Volume 39, number 29 October 11, 2013 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 ========= Luo T, Mohan K, Iglesias PA, Robinson DN. Molecular mechanisms of cellular mechanosensing Nat. Mater. 2013, in press. Mechanical forces direct a host of cellular and tissue processes. Although much emphasis has been placed on cell-adhesion complexes as force sensors, the forces must nevertheless be transmitted through the cortical cytoskeleton. Yet how the actin cortex senses and transmits forces and how cytoskeletal proteins interact in response to the forces is poorly understood. Here, by combining molecular and mechanical experimental perturbations with theoretical multiscale modelling, we decipher cortical mechanosensing from molecular to cellular scales. We show that forces are shared between myosin II and different actin crosslinkers, with myosin having potentiating or inhibitory effects on certain crosslinkers. Different types of cell deformation elicit distinct responses, with myosin and alpha-actinin responding to dilation, and filamin mainly reacting to shear. Our observations show that the accumulation kinetics of each protein may be explained by its molecular mechanisms, and that protein accumulation and the cellŐs viscoelastic state can explain cell contraction against mechanical load. Submitted by Douglas Robinson [dnr@jhmi.edu] --------------------------------------------------------------------------- Phosphorylation of chemoattractant receptors regulates chemotaxis, actin reorganization and signal relay Joseph A. Brzostowski1,*, Satoshi Sawai2, Orr Rozov1,ŕ, Xin-hua Liao3,¤, Daisuke Imoto4, Carole A. Parent5 and Alan R. Kimmel3,* 1Laboratory of Immunogenetics Imaging Facility, NIAID/NIH, Rockville, MD 20852, USA 2Graduate School of Arts and Sciences, University of Tokyo and PRESTO, JST, Tokyo 153-8902, Japan 3Laboratory of Cellular and Developmental Biology, NIDDK/NIH, Bethesda, MD 20892, USA 4Graduate School of Arts and Sciences, University of Tokyo, Tokyo 153-8902, Japan 5Laboratory of Cellular and Molecular Biology, NCI/NIH, Bethesda, MD 20892, USA *Authors for correspondence (jb363a@nih.gov; alank@helix.nih.gov) J Cell Sci126, 4614-4626 Migratory cells, including mammalian leukocytes and Dictyostelium, use G-protein-coupled receptor (GPCR) signaling to regulate MAPK/ERK, PI3K, TORC2/AKT, adenylyl cyclase and actin polymerization, which collectively direct chemotaxis. Upon ligand binding, mammalian GPCRs are phosphorylated at cytoplasmic residues, uncoupling G-protein pathways, but activating other pathways. However, connections between GPCR phosphorylation and chemotaxis are unclear. In developing Dictyostelium, secreted cAMP serves as a chemoattractant, with extracellular cAMP propagated as oscillating waves to ensure directional migratory signals. cAMP oscillations derive from transient excitatory responses of adenylyl cyclase, which then rapidly adapts. We have studied chemotactic signaling in Dictyostelium that express non- phosphorylatable cAMP receptors and show through chemotaxis modeling, single-cell FRET imaging, pure and chimeric population wavelet quantification, biochemical analyses and TIRF microscopy, that receptor phosphorylation is required to regulate adenylyl cyclase adaptation, long-range oscillatory cAMP wave production and cytoskeletal actin response. Phosphorylation defects thus promote hyperactive actin polymerization at the cell periphery, misdirected pseudopodia and the loss of directional chemotaxis. Our data indicate that chemoattractant receptor phosphorylation is required to co-regulate essential pathways for migratory cell polarization and chemotaxis. Our results significantly extend the understanding of the function of GPCR phosphorylation, providing strong evidence that this evolutionarily conserved mechanism is required in a signal attenuation pathway that is necessary to maintain persistent directional movement of Dictyostelium, neutrophils and other migratory cells. Submitted by Joe Brzostowski [brzostowskij@niaid.nih.gov] ============================================================== [End dictyNews, volume 39, number 29]