dictyNews Electronic Edition Volume 30, number 4 February 1, 2008 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 ========= Actin-based propulsive forces and myosin II-based contractile forces in migrating Dictyostelium cells Yoshiaki IWADATE and Shigehiko YUMURA Department of Functional Molecular Biology, Graduate School of Medicine, Yamaguchi University, Yamaguchi 753-8512, Japan J. Cell Sci., in press It has been suggested that myosin II exerts traction forces at the posterior ends and retracting pseudopods of migrating cells, but there is no direct evidence. Here, using a combination of total internal reflection fluorescence (TIRF) and force microscopies with high spatial resolution of about 400 nm, we simultaneously recorded GFP-myosin II dynamics and traction forces under migrating Dictyostelium cells. Accumulation of filamentous myosin II and a subsequent increase in traction forces were detected in pseudopods just before retraction. In the case of motor-less myosin II, traction forces did not increase after accumulation, suggesting that the source of the retraction force is the motor activity of accumulated myosin II. Simultaneous recording of F-actin and traction forces revealed that traction forces were exerted under spot-like regions where F-actin accumulated. Cells migrated in a direction counter to the sum of the force vectors exerted at each spot, suggesting that the stress spots act as scaffolds to transmit the propulsive forces at the leading edge generated by actin polymerization. Submitted by: Yoshiaki Iwadate [iwadate@yamaguchi-u.ac.jp] -------------------------------------------------------------------------------- SrfB, a member of the Serum Response Factor family of transcription factors, regulates starvation response and early development in Dictyostelium María Galardi-Castilla(1), Barbara Pergolizzi(2), Gareth Bloomfield(3), Jason Skelton(4), Al Ivens(4), Robert R. Kay(3), Salvatore Bozzaro(2) and Leandro Sastre(1). (1) Instituto de Investigaciones Biomédicas CSIC/UAM. Arturo Duperier, 4. 28029-Madrid. Spain (2) Dip. Scienze Cliniche e Biologiche, Università di Torino, Ospedale S. Luigi, Orbassano, Italy (3) MRC Laboratory of Molecular Biology. Hills Road, Cambridge, CB2 2QH, UK (4) Wellcome Trust Sanger Institute. Cambridge, Cambridgeshire, CB10 1SA, UK Develop. Biol., in press The Serum Response Factor (SRF) is an important regulator of cell proliferation  and differentiation. D. discoideum  srfB gene codes for an SRF homologue  and  is expressed in vegetative cells and during development under the control of  three alternative promoters, which show different cell-type specific patterns  of expression. The two more proximal promoters directed gene transcription in  prestalk AB, stalk and lower-cup cells. The generation of a strain where the  srfB gene has been interrupted (srfB-) has shown that this gene is required  for regulation of actin-cytoskeleton-related functions, such as cytokinesis  and macropinocytosis. The mutant failed to develop well in suspension, but  could be rescued by cAMP pulsing, suggesting a defect in cAMP signaling.  srfB- cells showed impaired chemotaxis to cAMP and defective lateral  pseudopodium inhibition. Nevertheless, srfB- cells aggregated on agar  plates and nitrocellulose filters two hours earlier than wild type cells, and  completed development, showing an increased tendency to form slug  structures. Analysis of wild type and srfB- strains detected significant  differences in the regulation of gene expression upon starvation.  Genes  coding for lysosomal and ribosomal proteins, developmentally-regulated  genes, and some genes coding for proteins involved in cytoskeleton  regulation were deregulated during the first stages of development.  Submitted by: Leandro Sastre [lsastre@iib.uam.es] ============================================================== [End dictyNews, volume 30, number 4]