Dicty News Electronic Edition Volume 17, number 11 November 3, 2001 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. ========================= Group Leader Position ========================= The MRC Laboratory for Molecular Cell Biology has just placed the following advert "The Medical Research Council (MRC) Cell Biology Unit, under the directorship of Professor Alan Hall FRS, was established in January this year within the Laboratory for Molecular Cell Biology (LMCB) at University College London (UCL). The LMCB is a multi-disciplinary collaboration between the MRC and UCL, with modern laboratory space and state of the art core facilities. We are now seeking new group leaders for the Cell Biology Unit. Current areas of interest within the LMCB include the cytoskeleton, receptor signalling, membrane traffic and proliferation/differentiation control. We are looking to strengthen these areas, but also to expand into other areas of molecular cell biology. We are keen to increase the number of groups using model organisms to address important aspects of cell biology. Career appointments are available for candidates with an established international reputation, while career-track appointments will be offered to scientists at an earlier career stage who have demonstrated potential. Salary will be negotiable and relocation expenses will be payable where appropriate. Please send your application together with a CV, an outline of future research plans and the name and contact details of three referees to Professor Alan Hall at MRC Laboratory for Molecular Cell Biology, University College London, Gower Street, London WC1E 6BT or as an e-mail attachment to alan.hall@ucl.ac.uk before 20 December 2001." The LMCB is definitely receptive to groups working on model systems: present groups include 1 nematode group, two Drosophila groups and my own Dictyostelium group. I have no doubt that good applications using these or other model systems to address cell biological problems will get a full and fair consideration. Adrian Harwood ============= Abstracts ============= S-adenosyl-L-homocysteine hydrolase is sequestered into actin rods in Dictyostelium discoideum spores. For CSM News Letter Yoshiro Kishi1, Teruko Sugo2, Dana Mahadeo3, David Cotter3 and Masazumi Sameshima1* 1. Electron 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. 2. Division of Cell and Molecular Medicine, Center for Molecular Medicine, Jichi Medical School, Yakushiji 3311-1, Tochigi, 329-0498, Japan. 3. Department of Biological Sciences, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, Canada N9B 3P4. Accepted in FEBS Letters Abstract Here we show evidence that S-adenosyl-L-homocysteine hydrolase (SAHH) is linked to the actin cytoskeleton. Actin rods formed in Dictyostelium discoideum spores during the final stage of development are structurally composed of novel bundles of actin filaments. SAHH only accumulates with actin at this stage of development in the life cycle of D. discoideum. Recently SAHH is believed to be a target for antiviral chemotherapy and suppressions of T cells. Our finding may contribute to designing novel antiviral and immunosuppressive drugs. ----------------------------------------------------------------------------- Assembly of gp80 adhesion complexes in Dictyostelium: receptor compartmentalization and oligomerization in membrane rafts. Harris, T.J.C., Ravandi, A. and Siu, C.-H. Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario. J Biol Chem 2001 Oct 16; [epub ahead of print] http://www.jbc.org/cgi/reprint/M108030200v1 The phospholipid-anchored membrane glycoprotein gp80 mediates cell-cell adhesion through a homophilic trans-interaction mechanism during Dictyostelium development and is enriched in a Triton X-100-insoluble floating fraction (TIFF). To elucidate how gp80 adhesion complexes assemble in the plasma membrane, gp80-gp80 and gp80-raft interactions were investigated. A low density raft-like membrane fraction was isolated using a detergent-free method. It was enriched in sterols, the phospholipid-anchored proteins gp80, gp138 and ponticulin, as well as DdCD36 and actin, corresponding to components found in TIFF. Chemical cross-linking revealed that gp80 oligomers were enriched in the raft-like membrane fraction, implicating stable oligomer-raft interactions. However, gp80 oligomers resisted sterol sequestration and were partially dissociated with Triton X-100, suggesting that compartmentalization in rafts was not solely responsible for their formation. The trans-dimer known to mediate adhesion was identified, but cis-oligomerization predominated and displayed greater accumulation during development. In fact, oligomerization was dependent on the level of gp80 expression and occurred among isolated gp80 extracellular domains, indicating that it was mediated by direct gp80-gp80 interactions. Rafts existed in gp80-null cells and such preexistent membrane domains may provide optimal microenvironments for gp80 cis-oligomerization and the assembly of adhesion complexes. ----------------------------------------------------------------------------- Cell-cell adhesion and signal transduction during Dictyostelium development Juliet C. Coates and Adrian J. Harwood Commentary in J. Cell Sci Summary The development of the non-metazoan eukaryote Dictyostelium discoideum displays many of the features of animal embryogenesis, including regulated cell-cell adhesion. During early development, two proteins, DdCAD-1 and csA, mediate cell-cell adhesion between amoebae as they form a loosely packed multicellular mass. The mechanism governing this process is similar to epithelial sheet sealing in animals. Although cell differentiation can occur in the absence of cell contact, regulated cell-cell adhesion is an important component of Dictyostelium morphogenesis, and a third adhesion molecule, gp150, is required for multicellular development past the aggregation stage. Cell-cell junctions that appear to be adherens junctions form during late stages of Dictyostelium development. Although not essential to establish the basic multicellular body plan, these junctions are required to maintain the structural integrity of the fruiting body. The Dictyostelium beta-catenin homologue Aardvark (Aar) is present in adherens junctions, which are lost in its absence. As in the case of its metazoan counterparts, Aar also has a function in cell signalling and regulates expression of the prespore gene psA. It is becoming clear that cell-cell adhesion is an integral part of Dictyostelium development. As in animals, cell adhesion molecules have a mechanical function, and may also interact with the signal transduction processes governing morphogenesis. ----------------------------------------------------------------------------- Complex glycosylation of Skp1 in Dictyostelium: implications for the modification of other eukaryotic cytoplasmic and nuclear proteins Christopher M. West1,3, Hanke van der Wel1, and Eric A. Gaucher2 1Dept. of Anatomy and Cell Biology, University of Florida College of Medicine, Gainesville, FL 32610-0235, and 2Dept. of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA 3 to whom correspondence should be addressed at Dept. of Anatomy and Cell Biology, 1600 SW Archer Road, University of Florida College of Medicine, Gainesville, FL 32610-0235, USA; phone 352-392-3329; fax 352-392-3305; email GLYCOBIOLOGY, in press Recently, complex O-glycosylation of the cytoplasmic/nuclear protein Skp1 has been characterized in the eukaryotic microorganism Dictyostelium. Skp1's glycosylation is mediated by the sequential action of a prolyl hydroxylase and five conventional sugar nucleotide-dependent glycosyltransferase activities that reside in the cytoplasm rather than the secretory compartment. The Skp1-HyPro GlcNAcTransferase, which adds the first sugar, appears to be related to a lineage of enzymes that originated in the prokaryotic cytoplasm and initiates mucin-type O-linked glycosylation in the lumen of the eukaryotic Golgi apparatus. GlcNAc is extended by a bifunctional glycosyltransferase that mediates the ordered addition of b1,3-linked Gal and a1,2-linked Fuc. The architecture of this enzyme resembles that of certain 2-domain prokaryotic glycosyltransferases. The catalytic domains are related to those of a large family of prokaryotic and eukaryotic, cytoplasmic, membrane-bound, inverting glycosyltransferases that modify glycolipids and polysaccharides prior to their translocation across membranes toward the secretory pathway or the cell exterior. The existence of these enzymes in the eukaryotic cytoplasm away from membranes, and their ability to modify protein acceptors, exposes a new set of cytoplasmic and nuclear proteins to potential prolyl hydroxylation and complex O-linked glycosylation. Recently described candidate targets include mammalian HIF-a, a-synuclein from the central nervous system, and an algal viral capsid protein. ----------------------------------------------------------------------------- [End Dicty News, volume 17, number 11]