CSM News Electronic Edition Volume 5, number 18 Dec. 30, 1995 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to CSM-News@worms.cmsbio.nwu.edu. Back issues of CSM-News, the CSM Reference database and other useful information is available by anonymous ftp from worms.cmsbio.nwu.edu [165.124.233.50], via Gopher at the same address, or by World Wide Web at the URL "http://worms.cmsbio.nwu.edu/dicty.html" =========== Abstracts =========== Origin and evolution of circular waves and spirals in Dictyostelium discoideum territories Eirikur Palsson* and Edward C. Cox Program in Applied and Computational Mathematics*, Department of Molecular Biology , Princeton University, Princeton, NJ 08544 PNAS, in press ABSTRACT Randomly distributed Dictyostelium discoideum cells form cooperative territories by signaling to each other with 3' 5'-cyclic adenosine monophosphate (cAMP). Cells initiate the process by sending out pulsatile signals which propagate as waves. With time, circular and spiral patterns form. We show that by adding spatial and temporal noise to the levels of an important regulator of external cAMP levels, the cAMP phosphodiesterase inhibitor, we can explain the natural progression of the system from randomly firing cells to circular waves whose symmetries break to form double and single- or multi-armed spirals. When phosphodiesterase inhibitor is increased with time, mimicking experimental data, the wavelength of the spirals shortens, and a proportion of them evolve into pairs of connected spirals. We compare these results to recent experiments, finding that the temporal and spatial correspondence between experiment and model is very close. ------------------------------------------------------------------------- Genetic Networks that Regulate Development in Dictyostelium William F. Loomis Center for Molecular Genetics, Department of Biology University of California San Diego, La Jolla CA 92093 Microbiological Reviews, in press Summary Genes and their RNA and protein products can be considered as nodes in genetic networks when they are connected to two or more components by either regulatory or physical interactions. Some of the genes which have recently been shown to play essential roles in development of Dictyostelium discoideum are analyzed in terms of the networks within which they function. Development is divided into four partially overlapping stages: aggregation, post-aggregation, cell type specialization and terminal differentiation. The molecular consequences of mutations in one or more of these developmental genes as well as the resulting morphological aberrations shed light on the normal physiological processes by which the cells become mutually responsive, form mounds where prestalk and prespore cells diverge, regulate the proportions of the major cell types, and finally form fruiting bodies where 80% of the cells are spores held up by the remaining cells within a stalk. Although only a small proportion of the total number of developmental genes in Dictyostelium have been characterized to date, their interactions allow us to make specific predictions concerning the network of cell type interactions. A working model is presented as a possible framework for positioning new developmental genes as they are discovered. ------------------------------------------------------------------ Seven Helix Chemoattractant Receptors Transiently Stimulate MAP Kinase in Dictyostelium: Role of Heterotrimeric G-Proteins Mineko Maeda1, Laurence Aubry1, Robert Insall2, Chris Gaskins1, Peter N. Devreotes2, and Richard A. Firtel1 1Department of Biology Center for Molecular Genetics University of California, San Diego 2Department of Biological Chemistry Johns Hopkins University School of Medicine J. Biol. Chem., in press. ABSTRACT MAP kinases are involved in controlling a cell's responses to a variety of stimuli and can be activated by both protein tyrosine kinase and G protein-coupled receptors. It was previously shown that Dictyostelium MAP kinase ERK2 is required for normal activation of adenylyl cyclase and erk2 null cells are aggregation-deficient. In this manuscript, we show that the Dictyostelium MAP kinase ERK2 is rapidly and transiently activated in response to the chemoattractant cAMP. This response requires cAMP receptors but is independent of the coupled Ga2 subunit and the only known Gb subunit. These data indicate that ligand-mediated receptor-activation of adenylyl cyclase requires two receptor-dependent pathways, one of which requires heterotrimeric G proteins including Ga2 and the only known Gb subunit, and the second of which requires ERK2. Our results suggest that ERK2 may be activated by a novel receptor-mediated pathway. -------------------------------------------------------------------------- [End CSM News, volume 5, number 18]