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dictyNews Volume 30 Number 18
dictyNews
Electronic Edition
Volume 30, number 18
June 6, 2008
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.
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Abstracts
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Antisense RNA Inhibition of the beta Subunit of the Dictyostelium discoideum
Mitochondrial Processing Peptidase Induces the Expression of
Mitochondrial Proteins
Koki Nagayama(1,2), Shiori Itono(2), Takashi Yoshida(2), Sei-ichi Ishiguro(2),
Hiroshi Ochiai(2,3), and Tetsuo Ohmachi*(2)
(1) Science of Bioresources, United Graduate School of Agricultural Sciences,
Iwate University, Morioka 020-8551, Japan
(2) Department of Biochemistry and Biotechnology, Faculty of Agriculture and
Life Science, Hirosaki University, Hirosaki 036-8561, Japan
(3) Creative Research Institutive Sousei (CRIS), Hokkaido University,
Sapporo 001-0021, Japan
* Correspondingu author:
Tel: +81-172-39-3774; Fax: +81-172-39-3750;
E-mail: tohmachi@cc.hirosaki-u.ac.jp
Bioscience, Biotechnology, and Biochemistry, in press
We cloned and characterized a cDNA encoding the Dictyostelium discoideum
beta subunit of mitochondrial processing peptidase (Ddb-MPP). Western blot
analysis of the mitochondrial subfractions revealed that Ddb-MPP is located
in the mitochondrial matrix and membrane, whereas Dda-MPP, another subunit
of DdMPP, is located only in the matrix. Although expression of Ddb-MPP
mRNA is down-regulated during early development, the level of the Ddb-MPP
protein is constant throughout the Dictyostelium life cycle. In a
transformant expressing the antisense RNA of the b-MPP gene, unexpectedly,
the b-MPP protein increased about 1.8-fold relative to the wild type, and
its mRNA increased 4.5-fold. Expression of other mitochondrial proteins,
a-MPP and Cox IV, was also induced. These results suggest that antisense
RNA inhibition of the beta-MPP gene induces gene expression of
mitochondrial proteins, presumably in a retrograde signaling manner.
This is the pathway of the transfer of information from mitochondria
to the nucleus.
Submitted by: Koki Nagayama [i205015@stu.hirosaki-u.ac.jp]
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Purinergic-mediated Ca(2+) influx in Dictyostelium discoideum.
Melanie J. Ludlow#, David Traynor+, Paul R. Fisher§ and Steven J. Ennion#
#Department of Cell Physiology and Pharmacology, University of Leicester,
PO Box 138, Leicester LE1 9HN, UK.
+MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 0QH, UK
§Department of Microbiology, La Trobe University, Melbourne VIC 3086,
Australia
Cell Calcium, in press
The presence of five P2X-like genes (p2xA-E) in Dictyostelium suggests
that nucleotides other than cAMP may act as extracellular signalling
molecules in this model eukaryote. However, p2xA was found to have an
exclusively intracellular localisation making it unclear whether
Dictyostelium utilise P2 receptors in a manner analogous to vertebrates.
Using an apoaequorin expressing strain we show here that Dictyostelium
do possess cell surface P2 receptors that facilitate Ca(2+) influx in
response to extracellular ATP and ADP (EC(50)=7.5muM and 6.1muM,
respectively). Indicative of P2X receptor activation, responses were
rapid reaching peak within 2.91+/-0.04s, required extracellular Ca(2+),
were inhibited by Gd(3+), modified by extracellular pH and were not
affected by deletion of either the single Gbeta or iplA genes.
Responses also remained unaffected by disruption of p2xA or p2xE
showing that these genes are not involved. Cu(2+) and Zn(2+)
inhibited purine-evoked Ca(2+) influx with IC(50) values of 0.9 and
6.3muM, respectively. 300muM Zn(2+) completely abolished the initial
large rapid rise in intracellular Ca(2+) revealing the presence of
an additional smaller, slower P2Y-like response. The existence of
P2 receptors in Dictyostelium makes this organism a valuable model
to explore fundamental aspects of purinergic signalling.
Submitted by: Steve Ennion [se15@leicester.ac.uk]
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Vacuole membrane protein 1 is an endoplasmic reticulum protein required
for organelle biogenesis, protein secretion and development
Javier Calvo-Garrido, Sergio Carilla-Latorre, Francisco Lázaro-Diéguez,
Gustavo Egea and Ricardo Escalante
Molecular Biology of the Cell, in press
Vacuole membrane protein 1 (Vmp1) is membrane protein of unknown
molecular function that has been associated with pancreatitis and
cancer. The social amoeba Dictyostelium discoideum has a vmp1-related
gene that we identified previously in a functional genomic study.
Loss-of-function of this gene leads to a severe phenotype that
compromises Dictyostelium growth and development. The expression of
mammalian Vmp1 in a vmp1- Dictyostelium mutant complemented
the phenotype, suggesting a functional conservation of the protein
among evolutionarily distant species and highlights Dictyostelium
as a valid experimental system to address the function of this gene.
Dictyostelium Vmp1 is an endoplasmic reticulum protein necessary
for the integrity of this organelle. Cells deficient in Vmp1 display
pleiotropic defects in the secretory pathway and organelle biogenesis.
The contractile vacuole, which is necessary to survive under hypoosmotic
conditions, is not functional in the mutant. The structure of the Golgi
apparatus, the function of the endocytic pathway and conventional protein
secretion are also affected in these cells. Transmission electron microscopy
of vmp1- cells showed the accumulation of autophagic features that suggests
a role of Vmp1 in macroautophagy. In addition to these defects observed at
the vegetative stage, the onset of multicellular development and early
developmental gene expression are also compromised.
Submitted by: Ricardo Escalante [rescalante@iib.uam.es]
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[End dictyNews, volume 30, number 18]
