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dictyNews Volume 19 Number 11
Dicty News
Electronic Edition
Volume 19, number 11
November 23, 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.
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Abstracts
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A checkpoint of growth/differentiation transition in the cell cycle and its
relevance to pattern formation in Dictyostelium development
Yasuo Maeda*, Kazunori Sasaki and Aiko Amagai
Department of Developmental Biology and Neurosciences, Graduate School of
Life Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan
Recent Research Developments in Biophysics and Biochemistry, in press
(a review article)
ABSTRACT
In general, growth and differentiation are mutually exclusive, but are
cooperatively controlled during the course of development. The cellular
slime mold Dictyostelium, a wonderful model organism, grows and multiplies
as long as nutrients are supplied, and its differentiation is triggered by
starvation. A strict checkpoint (PS-point) from which cells switch growth
to differentiation has been specified in the cell cycle of D. discoideum
Ax-2 cells. Thus, Ax-2 cells start differentiating from the PS-point in
response to starvation, indicating that one needs to combine data on events
occurring around the PS-point with those on starvation-induced events to
understand the mechanism controlling growth/differentiation transition (GDT).
As was expected from the presence of PS-point, the cell s positioning in
cell masses and the subsequent cell-type choice occur greatly depending on
the cell s phase in the cell cycle at the onset of starvation. Novel and
somewhat unexpected functions of mitochondria in cell movement and
differentiation are also referred.
submitted by: Yasuo MAEDA [ymaeda@mail.cc.tohoku.ac.jp]
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CONTRASTING ACTIVITIES OF THE AGGREGATIVE AND LATE PDSA PROMOTERS IN
DICTYOSTELIUM DEVELOPMENT.
Karin E. Weening1, Irene Verkerke-Van Wijk2, Christopher R. Thompson3,
Richard H. Kessin4, Gregory J. Podgorski5 and Pauline Schaap1
1School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
2Department of Biology, University of Leiden, 2333 AL Leiden, The Netherlands
3MRC Laboratory of Molecular Biology, Cambridge, CB2 2QH, UK
4Department of Anatomy and Cell Biology, College of Physicians and Surgeons
of Columbia University, New York, NY 10032, USA
5Department of Biology, Utah State University, Logan UT 84322-5305, USA
Developmental Biology, in press
ABSTRACT
Expression of the Dictyostelium PdsA gene from the aggregative (PdA)
and late (PdL) promoter is essential for aggregation and slug morphogenesis
respectively. We studied the regulation of the PdA and PdL promoters in
slugs using labile beta-galactosidase (gal) reporter enzymes. PdL was active
in prestalk cells as was also found with stable gal. PdA activity
decreased strongly in slugs from all cells except those at the rear. This
is almost opposite to PdA activity traced with stable gal, where slugs
showed sustained activity with highest levels at the front. PdA was down-
regulated after aggregation irrespective of stimulation with any of the
factors known to control gene expression. PdL activity was induced in
cell suspension by cAMP and DIF acting in synergy. However, a DIF-less
mutant showed normal PdL activity during development, suggesting that DIF
does not control PdL in vivo. Dissection of the PdL promoter showed that
all sequences essential for correct spatio-temporal control of promoter
activity are downstream of the transcription start site in a region between
-383 and -19 nucleotides relative to the start codon. Removal of
nucleotides to position -364 eliminated responsiveness to DIF and cAMP,
but normal PdL activity in prestalk cells in slugs was retained. Further
5' deletions abolished all promoter activity. This result also indicates
that the induction by DIF and cAMP as seen in cell suspensions is not
essential for PdL activity in normal development.
submitted by: Pauline Schaap [PSchaap@lsstaff.dundee.ac.uk]
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Formation of the outer layer of the Dictyostelium spore coat depends on the
inner layer protein SP85/PsB
Talibah Metcalf, Karen Kelley, Gregory W. Erdos, Lee Kaplan, and Christopher
M. West
Dept. of Anatomy and Cell Biology, College of Medicine, and Electron
Microscopy Core Laboratory, ICBR, University of Florida, Gainesville, FL
32610-0235 USA
Microbiology, in press
ABSTRACT
The Dictyostelium spore is surrounded by a 220-micron thick trilaminar coat
that consists of inner and outer electron dense layers surrounding a central
region of cellulose microfibrils. In previous studies, a mutant strain (TL56)
lacking three proteins associated with the outer layer exhibited increased
permeability to macromolecular tracers, suggesting that this layer
contributes to the coat permeability barrier. Electron microscopy now shows
that the outer layer is incomplete in the coats of this mutant, and consists
of a residual regular array of punctate electron densities. The outer layer
is also incomplete in a mutant lacking a cellulose-binding protein
associated with the inner layer, and these coats are deficient in an outer
layer protein and another coat protein. To examine the mechanism by which
this inner layer protein, SP85, contributes to outer layer formation,
various domain fragments were overexpressed in forming spores. Most of these
exert dominant negative effects similar to the deletion of outer layer
proteins but one construct, consisting of a fusion of the N-terminal and
Cys-rich C1-domain, induces a dense mat of novel filaments at the surface
of the outer layer. Biochemical studies show that the C1-domain binds
cellulose, and a combination of site-directed mutations that inhibits its
cellulose-binding activity suppresses outer layer filament induction. The
results suggest that, in addition to a previously described early role in
regulating cellulose synthesis, SP85 subsequently contributes a cross-
bridging function between cellulose and other coat proteins to organize
previously unrecognized structural elements in the outer layer of the coat.
submitted by: Chris West [westcm@anatomy.med.ufl.edu]
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A model for cGMP signal transduction in Dictyostelium in perspective of 25
years of cGMP research
Leonard Bosgraaf and Peter J.M. van Haastert
Department of Biochemistry, University of Groningen,Nijenborgh 4, 9747
AG Groningen, the Netherlands
Journal of Muscle Research and Cell Motility, Special Issue: Dictyostelium
Ed. Dietmar J. Manstein, in press
Abstract
About twenty-five years ago, it was discovered that cGMP is produced
intracellularly when cells are exposed to chemoattractants. Shortly
hereafter, cGMP-degrading and cGMP-producing activities were found in
Dictyostelium lysates, as well as cGMP-binding activity. In the eighties
several mutants were isolated displaying aberrant cGMP metabolism as well
as altered chemotaxis, suggesting that cGMP plays a role in chemotaxis.
Recently we identified the genes encoding guanylyl cyclases, cGMP-
phosphodiesterases and cGMP-binding proteins, that probably constitute
the main components of the cGMP signal transduction pathway. The encoding
proteins appear to be very different from proteins with the same function in
metazoa, and therefore their biochemistry is not always easily interpreted.
The aim of this review is to discuss the previously obtained biochemical
and functional data on cGMP in Dictyostelium in the perspective of the
recently identified genes.
submitted by: P.J.M.van.Haastert [P.J.M.van.Haastert@chem.rug.nl]
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cGMP signalling: different ways to create a pathway
Jeroen Roelofs1 , Janet L. Smith2 and Peter J.M. Van Haastert1
1, Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747
AG Groningen, the Netherlands
2, Boston Biomedical Research Institute, 64 Grove Street, Watertown,
Massachusetts 02472-2829, U.S.A.
Trends in Genetics, in press.
Abstract
A novel cGMP signalling cascade was uncovered in Dictyostelium, a eukaryote
that diverged from the lineage to metazoa after plants but before yeast. In
both Dictyostelium and metazoa, the ancient cAMP binding (cNB) motif of
bacterial CAP has been modified and assembled with other domains into cGMP-
target proteins. The domain structures of these cGMP targets, as well as the
enzymes responsible for cGMP synthesis and degradation, are entirely
different between Dictyostelium and metazoa, suggesting that different
cGMP-signalling pathways evolved in these two lineages.
submitted by: P.J.M.van.Haastert [P.J.M.van.Haastert@chem.rug.nl]
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[End Dicty News, volume 19, number 11]
