dictyNews Electronic Edition Volume 27, number 3 August 4, 2006 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. ============= Abstracts ============= Delineation of the roles played by RasG and RasC in cAMP-dependent signal transduction during the early development of Dictyostelium discoideum Parvin Bolourani, George B. Spiegelman and Gerald Weeks Department of Microbiology and Immunology, University of British Columbia Vancouver, BC, V6T 1Z3, Canada Corresponding author: Gerald Weeks email: gerwee@interchange.ubc.ca Tel: 604-822-6649 Fax: 604-822-6041 Mailing address: Life Sciences Centre, 2350 Health Sciences Mall, University of British Columbia Vancouver, BC, V6T 1Z3, Canada Molecular Biology of the Cell, in press Upon starvation, the cellular slime mold Dictyostelium discoideum initiates a program of development leading to formation of multicellular structures. The initial cell aggregation requires chemotaxis to cyclic AMP (cAMP) and relay of the cAMP signal by the activation of adenylyl cyclase (ACA), and it has been shown previously that the Ras protein RasC is involved in both processes. Insertional inactivation of the rasG gene resulted in delayed aggregation and a partial inhibition of early gene expression, suggesting that RasG also has a role in early development. Both chemotaxis and ACA activation were reduced in the rasG- cells, but the effect on chemotaxis was more pronounced. When the responses of rasG- cells to cAMP were compared with the responses of rasC- and rasC- rasG- strains, generated in otherwise isogenic backgrounds, these studies revealed that signal transduction through RasG is more important in chemotaxis and early gene expression, but that signal transduction through RasC is more important in ACA activation. Since the loss of either of the two Ras proteins alone did not result in a total loss of signal output down either of the branches of the cAMP signal-response pathway, there appears to be some overlap of function. Submitted by: Gerry Weeks [gerwee@interchange.ubc.ca] ----------------------------------------------------------------------------- WASP-Interacting Protein (WIPa) is Important for Actin Filament Elongation and Prompt Pseudopod Formation in Response to a Dynamic Chemoattractant Gradient Scott A. Myers, Laura R. Leper, and Chang Y. Chung Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37069 Molecular Biology of the Cell, In Press The role of WASP-interacting protein (WIP) in the process of F-actin assembly during chemotaxis of Dictyostelium was examined. Mutations of the WH1 domain of WASP led to a reduction in binding to WIPa, a newly identified homolog of mammalian WIP, a reduction of F-actin polymerization at the leading edge, and a reduction in chemotactic efficiency. WIPa localizes to sites of new pseudopod protrusion and colocalizes with WASP at the leading edge. WIPa increases actin elongation in vivo and in vitro in a WASP-dependent manner. WIPa overexpressing cells exhibit multiple microspike formation and defects in chemotactic efficiency due to frequent changes of direction. WIPa translocates to the cortical membrane upon uniform cAMP stimulation. This translocation appears to be dependent upon cortical F-actin assembly. Reduced expression of WIPa by expressing a hairpin WIPa (hp WIPa) construct resulted in more polarized cells that exhibit a delayed response to a new chemoattractant source due to delayed extension of pseudopod toward the new gradient. These results suggest that WIPa is important for actin filament elongation required for new pseudopod protrusion and prompt reorientation of cells toward a new gradient by initiating localized bursts of actin polymerization and/or elongation. Submitted by: Chang Chung [chang.chung@vanderbilt.edu] ============================================================================== [End dictyNews, volume 27, number 3]