CSM News Electronic Edition Volume 1, number 18 October 9, 1993 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 [129.105.233.50]. =========== ABSTRACTS =========== Folate responsiveness during growth and development of Dictyostelium: separate but related pathways control chemotaxis and gene regulation. Jurgen H. Blusch and Wolfgang Nellen* Max-Planck-Institut fur Biochemie, 82152 Martinsried, FRG Abstract: Folate controlled gene expression and chemotaxis have been examined in Dictyostelium wild type and mutant strains. We show that regulation of the discoidin genes is sensitive to folate in growing cells as well as in suspension development. The signal is transferred via the N10-methylfolate sensitive folate receptor sites, which also appear to confer the chemotactic response. The strain HG5145 has previously been isolated as a mutant which does not display chemotactic movement towards folate. Nevertheless, these cells are fully functional in folate mediated downregulation of discoidin I expression. The strain ga 93 has been isolated as an overproducer mutant of the cyclic nucleotide phosphodiesterase inhibitor. Simultaneously, these cells fail to downregulate discoidin I in response to folate but are fully functional in folate chemotaxis. Therefore we conclude that the pathways for chemotaxis and for gene regulation diverge downstream of a common receptor type. ----------------------------------------------------------- Microtubule centers and the interphase microtubule cytoskeleton in amoebae of the cellular slime molds (mycetozoans) Acytostelium leptosomum and Protostelium mycophaga. Bruno Guhl* and Urs-Peter Roos, Institute of Plant Biology, University of Zurich, Zurich, Switzerland. Cell Motil. Cytoskel., in press. We investigated the microtubule (MT) cytoskeleton and microtubule centers (MTC) in undifferentiated amoebae by indirect immunofluorescence with six monoclonal antitubulin antibodies, and by transmission electron microscopy and immunogold ultracytochemistry. Interphase ameobae of both species contain a distinct cytoplasmic complex of MTs, which is more elaborate in P. mycophaga. In A. leptosomum amoebae a single MTC is attached to each interphase nucleus at its pointed end, as in the other dictyostelid cellular slime molds Dictyostelium discoideum and Polysphondylium violaceum. Ultrastructurally, MTCs of A. leptosomum also resemble those of these two species: they consist of an electron-opaque core shaped like a stout rod, which is embedded, together with nodules, in a fuzzy matrix. The nodules are the points of origin of the MTs. In most amoebae of P. mycophaga there are two MTCs on opposite sides of and close to the nucleus, but many amoebae also contain a variable number of MTCs that are remote from the nucleus. They consist of a ring-shaped core with inner and outer diameters of ca. 130 nm and 340 nm. A plug sits in the ring and satellites are connected to the core by fine fibrils. The satellites are the points of origin of MTs. New MTCs are apparently formed during mitosis, the parent MTC probably serving as a template for the genesis of a new ring. The results support the notion that phylogenetically related organisms have similarly constructed MTCs and that these are dissimilar in less closely related organisms. ------------------------------------------------------------------ Kathleen V. Nolta and Theodore L. Steck (Department of Biochemistry and Molecular Biology, The University of Chicago) Isolation and Initial Characterization of the Bipartite Contractile Vacuole Complex from Dictyostelium discoideum. J. Biol. Chem. (in press) Abstract The contractile vacuoles complex serves to excrete excess cytosolic water from protists. In the amoeba, Dictyostelium discoideum, the organelle had a bipartite morphology: a large main vacuole marked by lumenal alkaline phosphatase (bladders) was surrounded by numerous satellite vacuoles (spongiomes). Bladders and spongiomes have now been purified for the first time. The spongiome membranes had a high density of surface projections identified as catalytically-active vacuolar proton pumps (V-H+-ATPase). Spongiomes were resolved from the pump-poor bladders by immunogold buoyant density shift with antibodies to the V-H+-ATPase; they contained little protein other than this pump. It appears that, following homogenization, most of the spongiome dissociated from bladders and populated the proton pump rich membrane fraction called acidosomes. Isolated bladders were enriched >40-fold in alkaline phosphatase and phosphodiesterase, the activities of which were >85% latent. Bladders depleted of spongiomes bore several distinctive polypeptides; they also had an excess of the basepieces of the proton pump over the catalytic heads. Bladder membranes were also lipid-rich and had a distinctivce lipid composition. We conclude that the contractile vacuole system in Dictyostelium is a complex of discrete, separable bladder and spongiome membranes. The V-H+-ATPase in the spongiome may catalyze the primary energy transduction step for pumping water out of the cytoplasm. ---------------------------------------------------------------------- [[End CSM-News, volume 1, number 18]]