Dicty News Electronic Edition Volume 9, number 11 November 1, 1997 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/dicty.html" =========== Abstracts =========== Selection for spiral waves in the social amoebae Dictyostelium Eiríkur Pálsson*, Kyoung J. Lee§, Raymond E. Goldstein, Jakob Franke||, Richard H. Kessin ||, and Edward C. Cox* Department of Molecular Biology and Department of Physics, Princeton University, Princeton, NJ 08544 Department of Anatomy and Cell Biology, College of Physicians & Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032 Proc. Natl. Acad. Sci USA, in press. Summary: Starving Dictyostelium amoebae emit pulses of the chemoattractant cAMP that are relayed from cell to cell as circular and spiral waves. We have recently modeled spiral wave formation in Dictyostelium. Our model suggests that a secreted protein inhibitor of an extracellular cAMP phosphodiesterase selects for spirals. Here we test the essential features of this prediction by comparing wave propagation in wild-type and inhibitor mutants. We find that mutants rarely form spirals. The territory size of mutant strains is approximately 50 times smaller than wild-type, and the mature fruiting bodies are smaller but otherwise normal. These results identify a mechanism for selecting one wave symmetry over another in an excitable system, and suggest that the phosphodiesterase inhibitor may be under selection because it helps regulate territory size. ------------------------------------------------------------------------- Myosin Localization During Cytokinesis in Live Cells James H. Sabry, Sheri L. Moores, Shannon Ryan, Ji-Hong Zang and James A. Spudich, Mol Biol Cell, in press. Abstract: Conventional myosin II plays a fundamental role in the process of cytokinesis where, in the form of bipolar thick filaments, it is thought to be the molecular motor that generates the force necessary to divide the cell. In Dictyostelium, the formation of thick filaments is regulated by the phosphorylation of three threonine residues in the tail region of the myosin heavy chain. We report here on the effects of this regulation on the localization of myosin in live cells undergoing cytokinesis. We imaged fusion proteins of the green fluorescent protein with wild type myosin and with myosins where the three critical threonines had been changed to either alanine or aspartic acid. We provide evidence that thick filament formation is required for the accumulation of myosin in the cleavage furrow and that if thick filaments are overproduced, this accumulation is markedly enhanced. This suggests that myosin localization in dividing cells is regulated by myosin heavy chain phosphorylation. ------------------------------------------------------------------------- The Cytoplasmic Dynein Heavy Chain is an Essential Gene Product in Dictyostelium. Michael P. Koonce and David A. Knecht Division of Molecular Medicine, Wadsworth Center. Albany, NY 12201-0509 and Department of Molecular and Cellular Biology. University of Connecticut Storrs, CT, 06269 Cell Motility and the Cytoskeleton, in press ABSTRACT We describe here three different approaches to perturb cytoplasmic dynein heavy chain (DHC) gene function in Dictyostelium: Integration of a marker into the heavy chain coding sequence by homologous recombination to disrupt transcription, expression of antisense RNA to inhibit translation, and expression of a 158 kDa amino-terminal coding region to perturb the native protein organization. By homologous recombination, we fail to obtain cells that lack an intact DHC gene product. Cells containing antisense orientation plasmids (but not sense) appear to die 4 to 6 days following transformation. Plasmids designed to overexpress an amino-terminal region of the DHC result in substantially reduced transformation efficiency. When expressed at low levels, the truncated amino-terminal product appears capable of dimerizing with an intact heavy chain or with itself, essentially producing a cargo-binding domain lacking mechanochemical activity. This, in turn, likely competes with the native protein’s function. These three approaches taken together indicate that the dynein heavy chain is an essential gene in Dictyostelium. ------------------------------------------------------------------------- Symmetry breaking in Dictyostelium morphogenesis: evidence that a combination of cell cycle stage and positional information dictates cell fate Tsuyoshi Araki, Tomoaki Abe*, Jeffrey Williams* and Yasuo Maeda Biological Institute, Graduate School of Science, Tohoku University, Aoba, Sendai 980-77, Japan and *MRC Laboratory For Molecular Biology and Department of Biology, University College of London, Gower St., London WC1E6BT, UK Developmental Biology, in press Abstract The event that visibly breaks the symmetry of the Dictyostelium aggregate is the formation of a nipple shaped tip at its apex but there has been considerable debate as to the equivalence of cells entering development, particularly with regard to the effect of cell cycle position at the onset of starvation. We show that there is a strong correlation between cell cycle position at time of starvation and subsequent expression of a marker of tip cell differentiation. Cells starved in late G2 phase selectively differentiate into tip cells. Previous evidence indicated that tip cells differentiate at the extreme periphery of the aggregate and then move to the apex. Taken in combination these data suggest that cell-cycle position at the onset of starvation affects differentiation fate by determining a cell's probable position within the aggregate, i.e. that both cell cycle and positional information are used to generate pattern. ------------------------------------------------------------------------- [End Dicty News, volume 9, number 11]