Dicty News Electronic Edition Volume 18, number 4 March 2, 2002 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu. Back issues of Dicty-News, the Dicty Reference database and other useful information is available at DictyBase--http://dictybase.org. ============= Abstracts ============= Correlates of developmental cell death in Dictyostelium discoideum Trupti Kawli, B.R. Venkatesh, P. Kevin Kennady*, Gopal Pande* and Vidyanand Nanjundiah Indian Institute of Science, Bangalore 560012, India and *Centre for Cellular and Molecular Biology, Hyderabad 500007 Differentiation, in press ABSTRACT We have studied the correlates of cell death during normal development in Dictyostelium discoideum. Our main findings are four. (i) There is a gradual increase in the number of cells with exposed phosphatidyl serine residues, an indicator of membrane asymmetry loss and increased permeability. Only presumptive stalk cells show this change in membrane asymmetry. Also, under conditions that promote calcium-induced stalk cell differentiation in cell monolayers, cells show an increase in cell membrane permeability. (ii) There is a gradual fall in mitochondrial membrane potential during development, again restricted to the presumptive stalk cells. (iii) The fraction of cells showing caspase-3 activity increases as development proceeds and then declines in the terminally differentiated fruiting body. (iv) There is an absence of internucleosomal cleavage of DNA, or DNA fragmentation. There is also no calcium and magnesium-dependent endonucleolytic activity seen in nuclear extracts from various developmental stages. However, nuclear condensation and peripheralization does occur in stalk cells. Thus, cell death in D.discoideum shows some, but not all, features of apoptosis as recognized in other multicellular systems. These findings argue against the emergence of a single mechanism of 'programmed cell death (PCD)' before multicellularity arose during evolution. ----------------------------------------------------------------------------- Lamellipodial localization of Dictyostelium myosin heavy chain kinase A is mediated via F-actin binding by the coiled-coil domain Paul A. Steimle(a), Lucila Licate(b), Graham P. Ct(c), and Thomas T. Egelhoff(b) (a)Department of Biology University of North Carolina at Greensboro, Greensboro, NC 27402; (b)Department of Physiology and Biophysics Case Western Reserve School of Medicine Cleveland, OH 44106; (c) Department of Biochemistry, Queen s University Kingston, Ontario, CANADA FEBS Letters, In Press ABSTRACT Myosin heavy chain kinase A (MHCK A) modulates myosin II filament assembly in the amoeba Dictyostelium discoideum. MHCK A localization in vivo is dynamically regulated during chemotaxis, phagocytosis, and other polarized cell motility events, with preferential recruitment into anterior F-actin rich structures. The current work reveals that an amino-terminal segment of MHCK A, previously identified as forming a coiled-coil, mediates anterior localization. MHCK A co-sediments with F-actin, and deletion of the amino- terminal domain eliminated actin binding. These results indicate that the anterior localization of MHCK A is mediated via direct binding to F-actin, and reveal the presence of an actin-binding function not previously detected by primary sequence evaluation of the coiled-coil domain. ----------------------------------------------------------------------------- Genetic and morphological evidence for two parallel pathways of cell cycle- coupled cytokinesis in Dictyostelium. Akira Nagasaki1, Eugenio L. de Hostos2 and Taro Q.P. Uyeda1 1: Gene Discovery Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8562, Japan; 2: Department of Cell Genetics, Exelixis Inc., South San Francisco, CA 94083-0511, USA J. Cell. Sci., in press. SUMMARY Myosin II-null cells of Dictyostelium discoideum cannot divide in suspension, consistent with the dogma that myosin II drives constriction of the cleavage furrow, and consequently, cytokinesis (cytokinesis A). Nonetheless, when grown on substrates, these cells exhibit efficient, cell cycle-coupled division, suggesting that they possess a novel, myosin II- independent, adhesion-dependent method of cytokinesis (cytokinesis B). Here we show that double mutants lacking myosin II and either AmiA or coronin, both of which are implicated in cytokinesis B, are incapable of cell cycle-coupled cytokinesis. These double mutants multiplied in number mainly by cytokinesis C, a third, inefficient method of cell division, which requires substrate adhesion and is independent on the cell cycle progression. In contrast, double mutants lacking AmiA and coronin were not sicker than each of the single mutant, indicating that the severe defects of myosin II-/ AmiA- or myosin II-/coronin- are not simple additive effects of two mutations. We take this as genetic evidence for two parallel pathways that both lead to cell cycle-coupled cytokinesis. This conclusion is supported by differences in morphological changes during cytokinesis of the mutant cell lines. ----------------------------------------------------------------------------- Mini review: Gene expression patterns in Dictyostelium using microarrays Gad Shaulsky and William F. Loomis Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030. Division of Biology, University of California, San Diego, La Jolla, CA 92093. Protist (in press) (no abstract) The promises and perils of microarray analyses of gene expression are considered and the results from recent microarray studies in Dictyostelium compared and summarized. The avenues open for future microarray studies are briefly discussed. ----------------------------------------------------------------------------- [End Dicty News, volume 18, number 4]