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dictyNews Volume 23 Number 18
Dicty News
Electronic Edition
Volume 23, number 18
December 10, 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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Activation of soluble guanylyl cyclase at the leading edge during
Dictyostelium chemotaxis
Douwe M. Veltman, Jeroen Roelofs, Ruchira Engel, Antonie J.W.G. Visser
and Peter J.M. Van Haastert
Department of Biochemistry, University of Groningen, Nijenborgh 4,
9747 AG Groningen, The Netherlands
Molecular Biology of the Cell, in press
Dictyostelium contains two guanylyl cyclases, GCA, a twelve-transmembrane
enzyme, and sGC, a homolog of mammalian soluble adenylyl cyclase. sGC
provides nearly all chemoattractant-stimulated cGMP formation and is
essential for efficient chemotaxis towards cAMP. We show that in resting
cells the major fraction of the sGC-GFP fusion protein localizes to the
cytosol and a small fraction is associated to the cell cortex. With the
artificial substrate Mn2+/GTP, sGC activity and protein exhibit a similar
distribution between soluble and particulate fraction of cell lysates.
However, with the physiological substrate Mg2+/GTP, sGC in the cytosol is
nearly inactive, while the particulate enzyme shows high enzyme activity.
Reconstitution experiments reveal that inactive cytosolic sGC acquires
catalytic activity with Mg2+/GTP upon association to the membrane.
Stimulation of cells with cAMP results in a 2-fold increase of
membrane-localized sGC-GFP, which is accompanied by an increase of the
membrane-associated guanylyl cyclase activity. In a cAMP gradient,
sGC-GFP localizes to the anterior cell cortex, suggesting that in
chemotacting cells, sGC is activated at the leading edge of the cell.
Submitted by: Peter van Haastert [P.J.M.van.Haastert@chem.rug.nl]
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Reverse genetic analyses of gamete-enriched genes revealed a novel regulator
of the cAMP signaling pathway in Dictyostelium discoideum
Tetsuya Muramoto, Shugaku Takedaa, Yoko Furuya, and Hideko Urushihara
Mechanisms of Development, in press.
Sexual development in Dictyostelium discoideum is initiated by the fusion of
oppo-site mating type cells to form zygote giant cells, which subsequently
gather and phagocytose surrounding cells for nutrition to form macrocysts.
Here we performed the targeting of 24 highly gamete-enriched genes we
previously isolated, and successfully generated knockout mutants for 16
genes and RNAi mutants for 20 genes including 6 genes without disruptants.
In the knockout mutants of two genes, cell aggregation to-ward the giant
cells was much less extensive and many cells remained around poorly formed
macrocysts. We named these genes tmcB and tmcC. Although macrocyst formation
of wild type cells was suppressed by the addition of exogenous cAMP, that
of knockout mutants of tmcB was much less sensitive. The mRNA level of
phosphodi-esterase (pde) was higher and that of its inhibitor (pdi) was
lower in the latter cells compared to the parental strains during sexual
development. Thus, tmcB appeared to be a novel regulator of the cAMP
signaling pathway specific to sexual development. Knockout mutants of
tmcC were indistinguishable from the wild type cells with respect to the
cAMP response, suggesting that this gene is relevant to other processes.
Submitted by: Hideko Urushihara [hideko@biol.tsukuba.ac.jp]
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Regulation of growth and differentiation in Dictyostelium
Yasuo Maeda
Department of Developmental Biology and Neurosciences, Graduate School of
Life Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan
International Review of Cytology, in press
In general, growth and differentiation are mutually exclusive, but
cooperatively regulated during the course of development. Thus the process
of cellÕs transition from growth to differentiation is of general
importance not only for the development of organisms but also the initiation
of malignant transformation, in which this process is reversed. 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 (GDT-point), from which cells start
differentiating in response to differentiation, has been specified in the
cell cycle of D. discoideum Ax-2 cells. Accordingly, integration of
GDT-point specific events with starvation-induced events is needed to
understand the mechanism regulating growth/differentiation transition (GDT).
A variety of inter- and intra-cellular signals are involved positively or
negatively in the initiation of differentiation, making a series of
cross-talks. As was expected from the presence of GDT-point, the cellÕs
positioning in cell masses and subsequent cell-type choice occur depending
on the cellÕs phase in the cell cycle at the onset of starvation. Since
novel and somewhat unexpected multiple functions of mitochondria in cell
movement, differentiation and pattern formation have been realized well in
Dictyostelium cells, they are reviewed in this article.
Submitted by: Yasuo Maeda [ymaeda@mail.tains.tohoku.ac.jp]
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[End Dicty News, volume 23, number 18] 
