Copy Link
Add to Bookmark
Report
dictyNews Volume 19 Number 01
Dicty News
Electronic Edition
Volume 19, number 1
July 20, 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.
======================
Position Available
======================
Postdoctoral fellow position available in our Cell Dynamics group
Applications are invited for a postdoctoral position funded by a Wellcome
Trust grant for 3 years, to study the mechanisms of phagocytosis by applying
proteomic and lipidomic analysis tools. We have recently established and
improved a phagosome purification protocol that allows access to large
quantities of lipids and proteins at any time point of phagosome maturation.
The preliminary molecular characterisation is in press in MBC and we want
to further the investigation of wild type and mutant strains with phagocytic
impairments. As the components of the complex machineries involved are
evolutionarily conserved, their molecular and cellular dissection in
Dictyostelium is directly relevant to unravel their functional importance
in higher organisms. A description of this and other projects of the group
is available at: http://www.bio.ic.ac.uk/research/tps/
The candidate should be motivated and enthusiastic about this area of
research. Proficiency in a variety of techniques, including cell culture,
single cell assays, biophysical and biochemical methods, microscopy and
bioinformatics will be a determining asset for the successful candidate.
For further details, please contact Dr. Thierry Soldati, Department of
Biological Sciences, Imperial College of Science, Technology and Medicine,
Exhibition Road, London, SW7 2AZ. E-mail t.soldati@ic.ac.uk. To apply,
please, send a full CV, a description of current research and interests,
and the name of two referees at the same address.
=============
Abstracts
=============
High resolution dissection of phagosome maturation reveals distinct membrane
trafficking phases
Daniel Gotthardt, Hans Jrg Warnatz, Oliver Henschel, Franz Brckert, Michael
Schleicher, and Thierry Soldati
Molecular Biology of the Cell, in press
Abstract
Molecular mechanisms of endocytosis in the genetically and biochemically
tractable professional phagocyte Dictyostelium discoideum reveal a striking
degree of similarity to higher eukaryotic cells. Pulse-chase feeding with
latex beads allowed purification of phagosomes at different maturation
stages. Gentle ATP-stripping of an actin meshwork entrapping contaminating
organelles resulted in a 10-fold increase in yield and purity, as confirmed
by EM. Temporal profiling of signaling, cytoskeletal and trafficking
proteins resulted in a complex molecular fingerprint of phagosome biogenesis
and maturation. First, nascent phagosomes were associated with coronin, and
rapidly received a lysosomal glycoprotein, LmpB. Second, at least two phases
of delivery of lysosomal hydrolases (CatD and CP34) were accompanied by
removal of plasma membrane components (PM4C4 and biotinylated surface
proteins). Third, a phase of late maturation, preparing for final exocytosis
of undigested material, included quantitative recycling of hydrolases and
association with vacuolin. Also, lysosomal glycoproteins of the Lmp family
showed distinct trafficking kinetics. The delivery and recycling of CatD was
directly visualized by confocal microscopy. This heavy membrane traffic of
cargos was precisely accompanied by regulatory proteins such as the Rab7
GTPases and the endosomal SNAREs Vti1 and VAMP7. This initial molecular
description of phagocytosis demonstrates the feasibility of a comprehensive
analysis of phagosomal lipids and proteins in genetically modified strains.
----------------------------------------------------------------------------
Possible Role of Contact Following in the Generation of Coherent Motion of
Dictyostelium Cells
Tamiki Umeda* and Kei Inouye**
*Department of Marine Engineering, Kobe University of Mercantile Marine,
Kobe 658-0022, Japan, **Department of Botany, Division of Biological Science,
Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
J. theor. Biol. in press
After aggregation by chemotaxis, cells of the cellular slime mold
Dictyostelium discoideum form a multicellular structure and show coherent
motion such as vortices. Here we present a mathematical model to explain
both aggregation and coherent motion of cells in two-dimensional space. The
model incorporates chemotactic response of cells and the cell's property,
called "contact following", to follow the other cells with which they are
in contact. Analytical study and computer simulation using the model show
that with contact following cells form circular clusters within which cell
rotation occurs. Unidirectional cell motion in a long belt of cells is
another type of solution of the model. Besides, contact following has an
effect to accelerate cell cluster merging. By considering the mechanism of
cell movement, possible explanations of contact following are proposed.
-----------------------------------------------------------------------------
Unique Behavior of a Dictyostelium Homologue of TRAP-1, Coupling with
Differentiation of D. discoideum cells
Tsuyoshi Morita, Aiko Amagai and Yasuo Maeda
Experimental Cell Research, in press
Dd-TRAP1 is a Dictyostelium homologue of TRAP-1, a human protein that binds
to the type1 tumor necrosis factor (TNF) receptor. TRAP-1 has a putative
mitochondrial localization sequence and shows significant homology to members
of HSP90 family. Although the TRAP-1 is mainly localized to mitochondria in
several mammalian cells, in certain tissues it is also localized at specific
extramitochondrial sites. In Dictyostelium cells, Dd-TRAP1 is predominantly
located in the cell membrane/cortex during growth and just after starvation.
Double staining of vegetatively growing cells with the anti-Dd-TRAP1 antibody
and TRITC-phalloidin has demonstrated co-localization of Dd-TRAP1 and F-actin
at the leading edge of cortical protrusions such as pseudopodes. Coupled
with differentiation, however, Dd-TRAP1 located at the cortical region is
translocated to mitochondria in spite of the absence of the mitochondrial
localization sequence at its N-terminus. The translocation of this protein
raises interesting and fundamental questions regarding possible mechanisms
by which the Dd-TRAP1 is involved in cellular differentiation.
-----------------------------------------------------------------------------
[End Dicty News, volume 19, number 1]
