Copy Link
Add to Bookmark
Report
dictyNews Volume 25 Number 12
dictyNews
Electronic Edition
Volume 25, number 12
November 18, 2005
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 dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
=============
Abstracts
=============
Comparing the Dictyostelium and Entamoeba Genomes
Reveals an Ancient Split in the Conosa Lineage
J. Song, Q. Xu, R. Olsen, W. F. Loomis, G. Shaulsky, A. Kuspa and
R. Sucgang
Verna and Marrs McLean Department of Biochemistry and Molecular Biology,
The Department of Human Genetics, and The Graduate Program in Structural
and Computational Biology and Molecular Biophysics,
Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
Section of Cell and Developmental Biology, Division of Biology, University
of California, San Diego, La Jolla, California 92093, USA
PLoS Computational Biology, in press
The Amebozoa are a sister clade to the fungi and the animals, but are
poorly sampled for completely sequenced genomes. The social amoeba
Dictyostelium discoideum and a mitochondriate pathogen Entamoeba histolytica
are the first Amoebozoa with genomes completely sequenced. Both organisms
are classified under the Conosa subphylum. To identify Amoebozoa-specific
genomic elements, we compared these two genomes to each other and to other
eukaryotic genomes. An expanded phylogenetic tree, built from the complete
predicted proteomes of 23 eukaryotes places the two amoebae in the same
lineage, although the divergence is estimated to be greater than that
between animals and fungi, and probably happened shortly after the Amoebozoa
split from the opisthokont lineage. Most of the 1500 orthologous gene
families shared between the two amoebae are also shared with plant, animal,
and fungal genomes. We found that only 42 gene families are distinct to the
amoeba lineage, among these are a large number of proteins the encode
repeats of the FNIP domain, and a transcription factor essential for proper
cell type differentiation in D. discoideum. These Amoebozoa-specific genes
may be useful in the design of novel diagnostics and therapies for amoebal
pathologies.
Supplementary data is available from
http://dictygenome.org/supplement/rsucgang/song_2005 .
Submitted by: Richard Sucgang [rsucgang@bcm.tmc.edu]
-----------------------------------------------------------------------------
Dictyostelium myosin-IE is a fast molecular motor involved in phagocytosis
Ulrike Duerrwang1, Setsuko Fujita-Becker1, Muriel Erent1, F. Jon Kull2,
Georgios Tsiavaliaris1,4, Michael A. Geeves3, and Dietmar J. Manstein1,4
1 Abteilung Biophysik, Max-Planck Institut fuer medizinische Forschung,
Jahnstr. 29, D-69120 Heidelberg, Germany
2 Dartmouth College, Department of Chemistry, 6128 Burke Laboratory,
Hanover, NH 03755
3 Department of Biosciences, University of Kent, Canterbury CT2 7NJ,
United Kingdom
4 Institut fuer Biophysikalische Chemie, OE 4350, Medizinische Hochschule
Hannover, Carl-Neuberg-Strasse 1, D-30623 Hannover, Germany
Journal Of Cell Science, in press
Class-I myosins are single-headed motor proteins, implicated in various
motile processes including organelle translocation, ion-channel gating, and
cytoskeleton reorganization. Here we describe the cellular localization of
myosin-IE and its role in the phagocytic uptake of solid particles and
cells. A complete analysis of the kinetic and motor properties of
Dictyostelium discoideum myosin-IE was achieved by the use of motor domain
constructs with artificial lever arms. Class-I myosins belonging to
subclass-IC like myosin-IE are thought to be tuned for tension maintenance
or stress sensing. Different from this prediction, our results show
myosin-IE to be a fast motor. Myosin-IE motor activity is regulated by
TEDS-site phosphorylation, which increases the coupling efficiency between
the actin and nucleotide binding sites 10-fold and the motile activity more
than 5-fold. Changes in the level of free Mg2+-ions, which are within the
physiological range, are shown to modulate the motor activity of myosin-IE
by inhibiting ADP-release.
Submitted by: Dietmar Manstein [manstein@bpc.mh-hannover.de]
-----------------------------------------------------------------------------
On the effects of cycloheximide on cell motility and polarisation in
Dictyostelium discoideum
Authors: Margaret Clotworthy* and David Traynor.
MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH,
England.
BioMed Central Cell Biology, in press
Background
Cycloheximide is a protein synthesis inhibitor that acts specifically on
the 60S subunit of eukaryotic ribosomes. It has previously been shown that
a short incubation of Dictyostelium discoideum amoebae in cycloheximide
eliminates fluid phase endocytosis.
Results
We found that treatment with cycloheximide also causes the amoebae to
retract their pseudopodia, round up and cease movement. Furthermore, fluid
phase endocytosis, phagocytosis and capping cease in the presence of 2mM
cycloheximide, although membrane uptake, as measured using FM1-43, is
unaffected. In the presence of cycloheximide, aggregation-competent amoebae
sensitive to cAMP, although round, can still localise CRAC, ABP120, PI3K and
actin polymerisation in response to a micropipette filled with cAMP. The
behaviour of wild-type amoebae in the presence of cycloheximide is
surprisingly similar to that of amoebae having a temperature-sensitive
version of NSF at the restrictive temperature.
Conclusions
Our results may suggest that, upon cycloheximide treatment, either a labile
protein required for polarised membrane recycling is lost, or a control
mechanism linking protein synthesis to membrane recycling is activated.
Submitted by: Margaret Clotworthy [clotworm@mrc-lmb.cam.ac.uk]
-----------------------------------------------------------------------------
Transcriptional regulation of post-aggregation genes in Dictyostelium by a
feed-forward loop involving GBF and LagC
Negin Iranfar, Danny Fuller, and William F. Loomis
Cell and Developmental Biology
Division of Biological Sciences,
University of California San Diego, La Jolla, CA 92093
Developmental Biology, in press
Expression profiles of developmental genes in Dictyostelium were determined
on microarrays during development of wild type cells and mutant cells lacking
either the DNA binding protein GBF or the signaling protein LagC. We found
that the mutant strains developed in suspension with added cAMP expressed
the pulse-induced and early adenylyl cyclase (ACA) dependent genes, but not
the later ACA dependent, post-aggregation genes. Since expression of lagC
itself is dependent on GBF, expression of the post-aggregation genes might
be controlled only by signaling from LagC. However, expression of lagC in a
GBF-independent manner in a gbfA- null strain did not result in expression
of the post-aggregation genes. Since GBF is necessary for accumulation of
LagC and both the DNA binding protein and the LagC signal transduction
pathway are necessary for expression of post-aggregation genes, GBF and
LagC form a feed-forward loop. Such network architecture is a common motif
in diverse organisms and can act as a filter for noisy inputs. Breaking the
feed-forward loop by expressing lagC in a GBF independent manner in a gbfA+
strain does not significantly affect the patterns of gene expression for
cells developed in suspension with added cAMP, but results in a significant
delay at the mound stage and asynchronous development on solid supports.
This feed-forward loop can integrate temporal information with morphological
signals to ensure that post-aggregation genes are only expressed after cell
contacts have been made.
Submitted by: Bill Loomis [wloomis@ucsd.edu]
==============================================================================
[End dictyNews, volume 25, number 12] 
