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dictyNews Volume 17 Number 11
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
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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.
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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.
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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.
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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 <westcm@college.med.ufl.edu>
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.
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[End Dicty News, volume 17, number 11]
