CSM News Electronic Edition Volume 4, number 6 February 18, 1995 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to CSM-News@worms.cmsbio.nwu.edu. Back issues of CSM-News, the CSM Reference database and other useful information is available by anonymous ftp from worms.cmsbio.nwu.edu [165.124.233.50], via Gopher at the same address, or by World Wide Web at the URL "http://worms.cmsbio.nwu.edu/dicty.html" =========== Abstracts =========== SPATIAL GRADIENTS OF CALCIUM IN THE SLUG OF Dictyostelium discoideum M. Azhar1, Shweta Saran1 and Vidyanand Nanjundiah1,2 1Developmental Biology and Genetics Laboratory, Indian Institute of Science, Bangalore 560012, India and 2Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560012, India. Current Science, in press. ABSTRACT The cells within the Dictyostelium slug differentiate according to a simple anterior/posterior dichotomy. This motivates a search for gradients of putative morphogens along its axis. Calcium may be one such morphogen. On the basis of observations made by using the calcium-sensitive fluorescent dyes fura-2 and chlortetracycline, we report that there are spatial gradients in cytoplasmic and sequestered calcium in the slug. Anteriorly located and genetically defined prestalk cells (ecmA/pstA, ecmB/pstAB) contain significantly higher levels of calcium than the prespore cells in the posterior. However, the proportion of 'calcium-rich' cells in the slug is greater than that of the subset of prestalk cells defined by the expression of the ecmA or ecmB genes. ------------------------------------------------------------------------- The in vivo role of annexin VII (synexin): Characterization of an annexin VII deficient Dictyostelium mutant indicates an involvement in Ca2+ regulated processes Volker During+, Francoise Veretout*, Richard Albrecht, Bettina Mohlbauer, Christina Schlatterer1, Michael Schleicher2 and Angelika A. Noegel Max-Planck-Institut fur Biochemie, Am Klopferspitz 18a, 82152 Martinsried, 1Fakultat fur Biologie, Universitat Konstanz, 78434 Konstanz, 2Ludwig-Maximilians-Universitat Munchen, Institut fur Zellbiologie, Schillerstrasse 42, 80336 Mnchen, F.R.G. J. Cell Sci., in press. Summary Dictyostelium discoideum cells harbor two annexin VII isoforms of 47 and 51 kDa which are present throughout development. In immunofluorescence and cell fractionation studies annexin VII was found in the cytoplasm and on the plasma membrane. In gene disruption mutants lacking both annexin VII isoforms growth, pinocytosis, phagocytosis, chemotaxis and motility were not significantly impaired under routine laboratory conditions, and the cells were able to complete the developmental cycle on bacterial plates. On non-nutrient agar plates development was delayed by three to four hours and a significant number of aggregates was no longer able to form fruiting bodies. Exocytosis as determined by measuring extracellular cAMP phosphodiesterase, a-fucosidase and a-mannosidase activity was unaltered, the total amounts of these enzymes were however lower in the mutant than in the wild type. The mutant cells were markedly impaired when they were exposed to low Ca2+ concentrations by adding EGTA to the nutrient medium. Under these conditions growth, motility and chemotaxis were severely affected. The Ca2+ concentrations were similar in mutant and wild type cells both under normal and Ca2+ limiting conditions, however the distribution was altered under low Ca2+ conditions in SYN- cells. The data suggest that annexin VII is not required for membrane fusion events but rather contributes to proper Ca2+-homeostasis in the cell. ----------------------------------------------------------------------