dictyNews
Electronic Edition
Volume 36, number 2
Jan 21, 2011
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Abstracts
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Nhe1 Is Essential For Potassium But Not Calcium Facilitation Of Cell Motility
And The Monovalent Cation Requirement For Chemotactic Orientation In
Dictyostelium discoideum
Daniel F. Lusche, Deborah Wessels, Daniel E. Ryerson, and David R. Soll
Eukaryotic Cell, in press
In Dictyostelium discoideum, extracellular K+ or Ca++ at concentrations of
40 and 20 mM, respectively, facilitates motility in the absence or presence of
a spatial gradient of chemoattractant. Facilitation results in maximum velocity,
cellular elongation, persistent translocation, suppression of lateral pseudopod
formation and myosin II localization in the posterior cortex. A lower threshold
concentration of 15 mM K+ or Na, or 5 mM Ca++, is required for chemotactic
orientation. Although the common buffer solutions used by D. discoideum
researchers to study chemotaxis contain sufficient concentrations of cations
for chemotactic orientation, the majority contain insufficient levels to facilitate
motility. Here, it is demonstrated that Nhe1, a plasma membrane protein, is
required for K+, but not Ca++, facilitation of cell motility, and for the lower
K+, but not Ca++, requirement for chemotactic orientation.
Submitted by Deb Wessels [[log in to unmask]]
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Cell-cycle checkpoint for transition from cell division to differentiation
Yasuo Maeda
Department of Developmental Biology and Neurosciences, Graduate School
of Life Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan
Develop. Growth Differ., in press
(Review article)
In general, growth and differentiation are mutually exclusive, but they are
cooperatively regulated during the course of development. Thus, the process
of a cell’s transition from growth to differentiation is of general importance for
the development of organisms, and terminally differentiated cells such as
nerve cells never divide. Meanwhile, the growth rate speeds up when cells
turn malignant. The cellular slime mold Dictyostelium discoideum grows and
multiplies as long as nutrients are supplied, and its differentiation is triggered
by starvation. A critical checkpoint (growth/differentiation transition or GDT
point), from which cells start differentiating in response to starvation, has been
precisely 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 GDTs. A variety of
intercellular and intracellular signals are involved positively or negatively
in the initiation of differentiation, making a series of cross-talks. As was
expected from the presence of the GDT point, the cell’s positioning in cell
masses and subsequent cell-type choices occur depending on the cell’s
phase in the cell cycle at the onset of starvation. Since novel and multiple
functions of mitochondria in various respects of development including the
initiation of differentiation have been directly realized in Dictyostelium cells,
they are also reviewed in this article.
Submitted by Yasuo Maeda [[log in to unmask]]
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Ethylene as a potent inducer of sexual development
Aiko Amagai
DGD, in press
(Review article)
A novel and critical function of ethylene, a potent plant hormone, has been well
documented in Dictyostelium, because it leads cells to the sexual development
(macrocyst formation) by inducing zygote formation. Zygote formation (sexual
cell fusion) and the subsequent nuclear fusion are the characteristic events
occurring during macrocyst formation. A novel gene, zyg1 was found to be
predominantly expressed during the sexual development, and its enforced
expression actually induces zygote formation. As expected, the zygote inducer,
ethylene enhances the expression of zyg1. Thus the function of ethylene has
been verified at all of individual (macrocyst formation), cellular (zygote formation),
and molecular levels (zyg1 expression). Based on our recent studies concerning
the behavior and function of the zyg1 product (ZYG1 protein), the signal
transduction pathways involved in zygote formation are proposed in this review.
Submitted by: Aiko Amagai [[log in to unmask]]
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[End dictyNews, volume 36, number 2]
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