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dictyNews Volume 22 Number 15
Dicty News
Electronic Edition
Volume 22, number 15
June 11, 2004
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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Distribution of alkaline phosphatase in vegetative Dictyostelium cells in
relation to the contractile vacuole complex
Margaret Clarke and Lucinda Maddera
Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, 73104
Eur. J. Cell Biol., in press.
(a special issue in honor of John Heuser)
The structure of the contractile vacuole complex of Dictyostelium
discoideum has long been a subject of controversy. A model that originated
from the work of John Heuser and colleagues described this osmoregulatory
organelle as an interconnected array of tubules and cisternae whose membranes
are densely populated with vacuolar proton pumps. A conflicting model
described this same organelle as bipartite, consisting of a pump-rich
spongiome and a pump-free bladder, the latter membranes being identified by
their alkaline phosphatase activity. In the present study we have employed
an antiserum specific for Dictyostelium alkaline phosphatase to examine the
distribution of this enzyme in vegetative cells. The antiserum labels
puncta, probably vesicles, that lie at or near the plasma membrane and are
sometimes, but only rarely, enriched near contractile vacuole membranes.
We conclude that alkaline phosphatase is not a suitable marker for
contractile vacuole membranes. We discuss these results in relation to the
two models of contractile vacuole structure and suggest that all data are
consistent with the first model.
Submitted by: Margaret Clarke [clarkem@omrf.ouhsc.edu]
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The XMAP215-family protein DdCP224 is required for cortical interactions of
microtubules
Andrea Hestermann and Ralph Graf*
A.-Butenandt-Institut/Zellbiologie, Ludwig-Maximilians-Universitt Mnchen,
Schillerstr. 42, D-80336 Mnchen, Germany
BMC Cell Biology 2004, 5:24, in press
Background: Interactions of peripheral microtubule tips with the cell cortex
are of crucial importance for nuclear migration, spindle orientation,
centrosome positioning and directional cell movement. Microtubule plus end
binding proteins are thought to mediate interactions of microtubule tips
with cortical actin and membrane proteins in a dynein-dependent manner.
XMAP215-family proteins are main regulators of microtubule plus end dynamics
but so far they have not been implicated in the interactions of microtubule
tips with the cell cortex.
Results: Here we show that overexpression of an N-terminal fragment of
DdCP224, the Dictyostelium XMAP215 homologue, caused a collapse of the
radial microtubule cytoskeleton, whereby microtubules lost contact with
the cell cortex and were dragged behind like a comet tail of an unusually
motile centrosome. This phenotype was indistinguishable from mutants
overexpressing fragments of the dynein heavy chain or intermediate chain.
Moreover, it was accompanied by dispersal of the Golgi apparatus and
reduced cortical localization of the dynein heavy chain indicating a
disrupted dynein/dynactin interaction. The interference of DdCP224 with
cortical dynein function is strongly supported by the observations that
DdCP224 and its N-terminal fragment colocalize with dynein and
coimmunoprecipitate with dynein and dynactin.
Conclusions: Our data show that XMAP215-like proteins are required for the
interaction of microtubule plus ends with the cell cortex in interphase
cells and strongly suggest that this function is mediated by dynein.
Submitted by: Ralph Graef [rgraef@lrz.uni-muenchen.de]
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Live cell spinning disk microscopy
RALPH GRAF1*, JENS RIETDORF2 AND TIMO ZIMMERMANN2
1) A.-Butenandt-Institut / Zellbiologie
Ludwig-Maximilians-Universitt Mnchen
Schillerstr. 42
80336 Mnchen, Germany
2) Advanced Light Microscopy Facility
European Molecular Biology Laboratory
Meyerhofstr. 1
69117 Heidelberg, Germany
Advances in Biochemical Engineering/Biotechnology, in press
Special Volume: Microscopic Techniques
Jens Rietdorf (Ed.)
In vivo microscopy of dynamic processes in cells and organisms requires
very fast and sensitive acquisition methods. Confocal laser scanning
microscopy is inherently speed-limited by the requirement of beam scanning
movements. In contrast to single beam scanning systems, the parallelized
approach of multi beam scanning is much faster. Spinning disk confocal
microscopes are therefore very suited for fast in vivo imaging. The
principles of spinning disk microscopy will be explained in this chapter
and a thorough comparison of the performance of single beam and multi beam
scanning systems is made and illustrated with an example of in vivo imaging
in Dictyostelium discoideum.
Submitted by: Ralph Graef [rgraef@lrz.uni-muenchen.de]
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Molecular and functional analysis of the Dictyostelium centrosome
Ralph Graf, Christine Daunderer and Irene Schulz
Adolf-Butenandt-Institut / Zellbiologie, Schillerstr. 42, D-80336 Mnchen,
Germany
Int. Rev. Cytol., in press
The centrosome is a non-membranous, nucleus-associated organelle which
functions not only as the main microtubule-organizing center but also as
a cell cycle control unit. How the ~100 different proteins that make up a
centrosome contribute to centrosome function is still largely unknown.
Considerable progress in the understanding of centrosomal functions can be
expected from comparative cell biology of morphologically different
centrosomal structures fulfilling conserved functions. Dictyostelium is an
alternative model organism for centrosome research in addition to yeast
and animal cells. With the elucidation of the morphological changes and
dynamics of centrosome duplication, the establishment of a centrosome
isolation protocol, and the identification of many centrosomal components
there is a solid basis for understanding the biogenesis and function of
this fascinating organelle. Here we give an overview of the prospective
protein inventory of the Dictyostelium centrosome based on database
searches. Moreover, we focus on the comparative cell biology of known
components of the Dictyostelium centrosome including the g-tubulin complex
and the homologues of centrin, Nek2, XMAP215 and EB1.
Submitted by: Ralph Graef [rgraef@lrz.uni-muenchen.de]
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[End Dicty News, volume 22, number 15]
