Dicty News Electronic Edition Volume 15, number 8 October 21, 2000 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@nwu.edu. Back issues of Dicty-News, the Dicty Reference database and other useful information is available at the Dictyostelium Web Page "http://dicty.cmb.nwu.edu/dicty" ============== Abstracts ============== Role of esterase gp70 and its influence on growth and development of Dictyostelium discoideum Aidong Yuan and Catherine P. Chia School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, N eraska 68588-0118, USA Experimental Cell Research, in press ABSTRACT: Gp70 is an esterase originally called crystal protein because of its presence in crystalline structures in aggregation-competent Dictyostelium discoideum cells. Although postulated to break down spore coats, the function of gp70 in vivo was incompletely investigated. Our immunolocalization and biochemical studies of vegetative D. discoideum amoebae show that gp70 was recruited to phagosomes and found in lysosomes. Purified gp70 was effective at hydrolyzing napthyl substrates with acyl chains typical of lipids and lipopolysaccharides, indicating that the gp70 was involved in digesting endocytosed molecules. The activity of purified gp70 was inhibited by reductants that retarded its eletrophoretic mobility, and verified the presence of intramolecular disulfide bonds predicted by its amino acid sequence. Compared to wild type cells, cells overexpressing gp70 were more phagocytically active, had shorter generation times and produced more fruiting bodies per unit area, while cells lacking gp70 were phagocytically less active with longer doubling times, developed more slowly, and had significantly fewer fruiting bodies per unit area. Consistent with the phenotype of a disrupted metabolism, a third of the gp70-minus cells were large and multinucleated. Together, these results indicated that despite its crystalline appearance, gp70 was an active esterase involved in both the growth and development of D. discoideum. ---------------------------------------------------------------------------- Novel Actin Cytoskeleton: Actin Tubules Masazumi Sameshima1, Yoshiro Kishi1, Masako Osumi2, Dana Mahadeo3, and David A. Cotter3 1Electron Microscopy Center, The Tokyo Metropolitan Institute of Medical Science, Tokyo Metropolitan Organization for Medical Research, 3-18-22 Honkomagome, Bunkyo-ku, Tokyo 113-8613, Japan. 2Department of Chemical and Biological Sciences, Faculty of Science, Japan Women's University, Bunkyo-ku, Tokyo 112-8681, Japan. 3Department of Biological Sciences, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, N9B 3P4, Canada. Cell Structure and Function, in press. ABSTRACT: In spores of Dictyostelium discoideum three-actin filaments are bundled to form a novel tubular structure and the tubules are then organized into rods. The tubular structures we will term actin tubules. Actin tubules are reconstructed from the supernatant of spore homogenates, while the usual actin filaments were bundled after incubation of supernatants from growing cells. Alpha-actinin, ABP-120 and EF-1 alpha are not essential for rod formation. Cofilin is a component of the cytoplasmic rods but few cofilin molecules are included in the nuclear rods. The viability of spores lacking actin rods is very low, and the spore shape is round instead of capsular. The rods can be fragmented by pressure, indicating that the rods may be effective in absorbing physical pressure. The complex organization of actin filaments, actin tubules and rods may be required for spores to achieve complete dormancy and maintain viability. ---------------------------------------------------------------------------- The role of DIF-1 signalling in Dictyostelium development Christopher R. L. Thompson and Robert R. Kay MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH, England Molecular Cell, in press Abstract We have constructed a mutant blocked in the biosynthesis of DIF-1, a chlorinated signal molecule proposed to induce differentiation of both major prestalk cell types formed during Dictyostelium development. Surprisingly, the mutant still forms slugs retaining one prestalk cell type, the pstA cells, and can form mature stalk cells. However, the other major prestalk cell type, the pstO cells, is missing. Normal pstO cell differentiation, and their patterning in the slug, is restored by development on a uniform concentration of DIF-1. We conclude that pstO and pstA cells are in fact induced by separate signals and that DIF-1 is the pstO inducer. Positional information, in the form of DIF-1 gradients, is evidently not required for pstO cell induction. ---------------------------------------------------------------------------- [End Dicty News, volume 15, number 8]