Copy Link
Add to Bookmark
Report
dictyNews Volume 39 Number 31
dictyNews
Electronic Edition
Volume 39, number 31
November 8, 2013
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.
Follow dictyBase on twitter:
http://twitter.com/dictybase
dictyBase has a job opening! http://dictybase.org/dictybase_jobs.html
=========
Abstracts
=========
Loss of cAMP-specific phosphodiesterase rescues spore
development in G protein mutant in Dictyostelium
David J. Schwebs, Hoai-Nghia Nguyen, Jamison A. Miller,
Jeffrey A. Hadwiger
Cellular Signalling, in press
Cyclic AMP (cAMP) is an important intracellular signaling molecule
for many G protein-mediated signaling pathways but the specificity of
cAMP signaling in cells with multiple signaling pathways is not well-
understood. In Dictyostelium, at least two different G protein signaling
pathways, mediated by the Galpha-2 and Galpha-4 subunits, are
involved with cAMP accumulation, spore production, and chemotaxis
and the stimulation of these pathways results in the activation of ERK2,
a mitogen-activated protein kinase that can down regulate the cAMP-
specific phosphodiesterase RegA. The regA gene was disrupted in
galpha-2- and galpha-4- cells to determine if the absence of this
phosphodiesterase rescues the development of these G protein
mutants as it does for erk2- mutants. The regA- mutation had no major
effects on developmental morphology but enriched the distribution of
the Galpha- mutant cells to the prespore/prestalk border in chimeric
aggregates. The loss of RegA function had no effect on Galpha-4-
mediated folate chemotaxis. However, the regA gene disruption in
galpha-4- cells, but not in galpha-2- cells, resulted in a substantial
rescue and acceleration of spore production. This rescue in sporulation
required cell autonomous signaling because the precocious sporulation
could not be induced through intercellular signaling in chimeric
aggregates. However, intercellular signals from regA- strains increased
the expression of the prestalk gene ecmB and accelerated the
vacuolization of stalk cells. Intercellular signaling from galpha-4-regA-
strain did not induce ecmA gene expression indicating cell-type
specificity in the promotion of prestalk cell development. regA gene
disruption in a Galpha-4HC (Galpha-4 overexpression) strain did not
result in precocious sporulation or stalk cell development indicating
that elevated Galpha-4 subunit expression can mask regA- associated
phenotypes even when provided with wild-type intercellular signaling.
These finding indicate that the Galpha-2 and Galpha-4-mediated
pathways provide different contributions to the development of spores
and stalk cells and that the absence of RegA function can bypass
some but not all defects in G protein regulated spore development.
Submitted by Jeff Hadwiger [jeff.hadwiger@okstate.edu]
---------------------------------------------------------------------------
Control of cell differentiation by mitochondria, typically evidenced in
Dictyostelium development
Yasuo Maeda1* and Junji Chida2
1Department of Developmental Biology and Neurosciences,
Graduate School of Life Sciences, Tohoku University, Aoba,
Sendai 980-8578, Japan; E-mail: kjygy352@ybb.ne.jp;
2Division of Molecular Neurobiology, Institute for Enzyme Research,
The University of Tokushima, Kuramoto-cho, Tokushima 770-8503,
Japan; E-mail: jchida@tokushima-u.ac.jp.
*Author to whom all correspondence should be addressed:
E-mail: kjygy352@ybb.ne.jp; Tel. & Fax: +81-22-224-2863
Biomolecules [Special Issue "Focus Update in Biomolecules"] (MDPI), in press
Review
In eukaryotic cells, mitochondria are self-reproducing organelles with
their own DNA and they play a central role in adenosine triphosphate
(ATP) synthesis by respiration.Increasing evidence indicates that
mitochondria also have critical and multiple functions in the initiation
of cell differentiation, cell-type determination, cell movement, and
pattern formation. This has been most strikingly realized in
development of the cellular slime mold Dictyostelium. For example,
the expression of the mitochondrial ribosomal protein S4 (mt-rps4)
gene is required for the initial differentiation. The Dictyostelium
homologue (Dd-TRAP1) of TRAP-1 (tumor necrosis receptor-
associated protein 1), a mitochondrial molecular chaperone belonging
to the Hsp90 family, allows the prompt transition of cells from growth
to differentiation through a novel prestarvation factor (PSF-3) in growth
medium. Moreover, a cell-type-specific organelle named a prespore-
specific vacuole (PSV) is constructed by mitochondrial transformation
with the help of the Golgi complex. Mitochondria are also closely
involved in a variety of cellular activities including CN-resistant
respiration and apoptosis. These mitochondrial functions are reviewed
in this article, with special emphasis on the regulation of Dictyostelium
development.
Keywords: differentiation; mitochondria; mitochondrial ribosomal protein
S4 (mt-RPS4); tumor necrosis receptor-associated protein 1 (TRAP-1);
CN-resistant respiration; prespore-specific vacuole (PSV);
Dictyostelium; ESC
Submitted by Yasuo Maeda [kjygy352@ybb.ne.jp]
---------------------------------------------------------------------------
Identification of a Farnesol Analogue as a Ras Function Inhibitor using
both an in vivo Ras activation sensor and phenotypic screening approach.
Kamalakkannan Srinivasan, Thangaiah Subramanian, H. Peter Spielmann,
and Chris Janetopoulos*
Molecular and Cellular Biochemistry, in press
Mutation in Ras isoforms such as K-Ras, N-Ras, H-Ras contributes to
roughly 85%, 15% and 1% of human cancers, respectively. Proper
membrane targeting of these Ras isoforms, a prerequisite for Ras activity,
requires farnesylation or geranylgeranylation at the C-terminal CAAX box.
We devised an in vivo screening strategy based on monitoring Ras
activation and phenotypic physiological outputs for assaying synthetic
Ras function inhibitors (RFI). Ras activity was visualized by the
translocation of RBDRaf1-GFP to activated Ras at the plasma membrane.
By using this strategy, we screened one synthetic farnesyl substrate
analog (AGOH) along with nine putative inhibitors and found that only
m-CN-AGOH inhibited Ras activation. Phenotypic analysis of starving
cells could be used to monitor polarization, motility and the inability of
these treated cells to aggregate properly during fruiting body formation.
Incorporation of AGOH and m-CN-AGOH to cellular proteins was detected
by western blot. These screening assays can be incorporated into a high
throughput screening format using Dictyostelium discoideum and
automated microscopy to determine effective RFIs. These RFI
candidates can then be further tested in mammalian systems.
Submitted by Chris Janetopoulos [c.janetopoulos@vanderbilt.edu]
---------------------------------------------------------------------------
A microfluidic-enabled mechanical microcompressor for the
immobilization of live single- and multi-cellular specimens.
Yingjun Yan, Liwei Jiang, Karl J. Aufderheide, Gus A. Wright, Alexander
Terekhov, Lino Costa, Kevin Qin, W. Tyler McCleery, John J. Fellenstein,
Alessandro Ustione, J. Brian Robertson, Carl Hirschie Johnson,
David W. Piston, M. Shane Hutson, John P. Wikswo, William Hofmeister,
Chris Janetopoulos*
Microscopy and Microanalysis, in press
A microcompressor is a precision mechanical device that flattens and
immobilizes living cells and small organisms for optical microscopy,
allowing enhanced visualization of sub-cellular structures and organelles.
We have developed an easily fabricated device which can be equipped
with microfluidics, permitting the addition of media or chemicals during
observation. This device can be used on both upright and inverted
microscopes, The apparatus permits micrometer precision flattening
for nondestructive immobilization of specimens as small as a bacterium,
while also accommodating larger specimens, such as Caenorhabditis
elegans, for long-term observations. The compressor mount is removable
and allows easy specimen addition and recovery for later observation.
Several customized specimen beds can be incorporated into the base.
To demonstrate the capabilities of the device, we have imaged numerous
cellular events in several protozoan species, in yeast cells, and in
Drosophila melanogaster embryos. We have been able to document
previously unreported events, and also perform photobleaching
experiments, in conjugating Tetrahymena thermophila.
Submitted by Chris Janetopoulos [c.janetopoulos@vanderbilt.edu]
==============================================================
[End dictyNews, volume 39, number 31]
