dictyNews Electronic Edition Volume 35, number 4 July 23, 2010 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 ========= Expression of Actin Tyr53Ala in Dictyostelium Disrupts the Cytoskeleton and Inhibits Intracellular and Intercellular Chemotactic-Signaling Shi Shu,* Xiong Liu,* Paul W. Kriebel,† Myoung-Soon Hong,*, Mathew P. Daniels,‡ Carole A. Parent,† and Edward D. Korn* From the *Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, †Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, ‡Electron Microscopy Core Facility, National Heart, Lung and Blood Institute, NIH, Bethesda, MD 20892 Running Head: Inhibition of cAMP signaling by actin Tyr53Ala mutant Address correspondence to: Edward D. Korn, Ph.D., Laboratory of Cell Biology, NHLBI, NIH, Building 50, Room 2517, 9000 Rockville Pike, Bethesda, MD 20892. Fax: 301-402-1519; edk@nih.gov J. Biol. Chem., in press We showed previously that phosphorylation of Tyr-53, or its mutation to Ala, inhibits actin polymerization in vitro with formation of aggregates of short filaments, and that expression of Y53A-actin in Dictyostelium blocks differentiation and development at the mound stage (Liu et al. (2006) Proc. Natl. Acad. Sci. U.S.A. 103, 13694-13699; Liu et al. (2010) J. Biol. Chem. 285, 9729-9739). We now show that expression of Y53A-actin, which does not affect cell growth, phagocytosis or pinocytosis, inhibits the formation of head-to-tail cell streams during cAMP-induced aggregation, although individual amoebae chemotax normally. We show that expression of Y53A-actin causes a 50% reduction of cell-surface cAMP-receptors, and inhibits cAMP-induced increases in adenylyl cyclase A activity, phosphorylation of ERK2 and actin polymerization. Trafficking of vesicles containing adenylyl cyclase A to the rear of the cell and secretion of the ACA-vesicles are also inhibited. The actin cytoskeleton of cells expressing Y53A-actin is characterized by numerous short filaments, and bundled and aggregated filaments similar to the structures formed by copolymerization of purified Y53A-actin and wild-type actin in vitro. This disorganized actin cytoskeleton may be responsible for the inhibition of intracellular and intercellular cAMP signaling in cells expressing F-Y/A-actin. Submitted by Edward Korn [edk@nih.gov] -------------------------------------------------------------------------------- Ca++ Chemotaxis in Dictyostelium discoideum Amanda Scherer, Spencer Kuhl, Deborah Wessels, Daniel F. Lusche, Brent Raisley and David R. Soll Journal of Cell Science, in press Using a newly developed microfluidic chamber, it is demonstrated in vitro that Ca++ functions as a chemoattractant of aggregation-competent D. discoideum amoebae, that parallel spatial gradients of cAMP and Ca++ are more effective than either alone and that cAMP functions as a stronger chemoattractant than Ca++ . Effective Ca++ gradients are extremely steep compared to effective cAMP gradients. This presents a paradox, since there is no indication to date that steep Ca++ gradients are generated in aggregation territories. However, given that Ca++ chemotaxis is co-acquired with cAMP chemotaxis during development, we speculate on the role Ca++ chemotaxis might play and the possibility that steep, transient Ca++ gradients may be generated during natural aggregation in the interstitial regions between cells. Submitted by Deborah Wessels [deborah-wessels@uiowa.edu] ============================================================== [End dictyNews, volume 35, number 4]