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dictyNews Volume 40 Number 28
dictyNews
Electronic Edition
Volume 40, number 28
November 07, 2014
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.
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=========
Abstracts
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Article for the ÒFree-living amoebae Special IssueÓ:Isolation and
characterisation of various amoebophagous fungi and evaluation of
their prey spectrum
Rolf Michel, JuliaWalochnik, Patrick Scheid
Experimental Parasitology
This article gives an overview on the isolation and
characterisation of endoparasitic fungi invading freeliving
amoebae (FLA), including the ones forming thalli inside their
hosts such as Cochlonema euryblastum and also the predatory
fungi which capture amoebae by adhesive hyphae. They trap,
intrude, and exploit amoebal trophozoites such as Acaulopage
spp. and Stylopage spp. Previous phylogenetic studies proved
Cochlonema to be a member of the Zoopagales. The genetic
investigation of Acaulopage tetraceros demonstrated its close
relationship to Cochlonema. Co-cultivation of A. tetraceros
with a number of FLA revealed a great prey spectrum of this
amoebophageous fungus. In addition it was shown that solitary
amoebal stages of slime moulds such as Dictyostelium sp. and
Physarum sp. are also suited as welcome prey amoebae.
Submitted by Rolf Michel [r.michel1@gmx.de]
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The Social Amoeba Polysphondylium pallidum Loses Encystation and
Sporulation, but Can Still Erect Fruiting Bodies in the
Absence of Cellulose.
Du Q, Schaap P.
Protist. 2014 Jul 14;165(5):569-579.
doi: 10.1016/j.protis.2014.07.003.
Amoebas and other freely moving protists differentiate into
walled cysts when exposed to stress. As cysts, amoeba pathogens
are resistant to biocides, preventing treatment and eradication.
Lack of gene modification procedures has left the mechanisms of
encystation largely unexplored. Genetically tractable Dictyostelium
discoideum amoebas require cellulose synthase for formation of
multicellular fructifications with cellulose-rich stalk and spore
cells. Amoebas of its distant relative Polysphondylium pallidum
(Ppal), can additionally encyst individually in response to stress.
Ppal has two cellulose synthase genes, DcsA and DcsB, which we
deleted individually and in combination. Dcsa- mutants formed
fruiting bodies with normal stalks, but their spore and cyst walls
lacked cellulose, which obliterated stress-resistance of spores and
rendered cysts entirely non-viable. A dcsa-/dcsb- mutant made no
walled spores, stalk cells or cysts, although simple fruiting
structures were formed with a droplet of amoeboid cells resting on
an sheathed column of decaying cells. DcsB is expressed in prestalk
and stalk cells, while DcsA is additionally expressed in spores and
cysts. We conclude that cellulose is essential for encystation and
that cellulose synthase may be a suitable target for drugs to
prevent encystation and render amoeba pathogens susceptible to
conventional antibiotics.
Submitted by Qingyou Du [q.du@dundee.ac.uk]
----------------------------------------------------------------------
Deckstein, J., van Appeldorn, J., Tsangarides, M., Yiannakou,
K., Mller, R., Stumpf, M., Sukumaran, S. K., Eichinger, L.,
Noegel, A. A., Riyahi, T. Y.
The Dictyostelium discoideum GPHR ortholog is an ER and Golgi
protein with roles during development.
Eukaryotic Cell, in press
The Dictyostelium discoideum GPHR (Golgi pH regulator)/Gpr89 is
a developmentally regulated transmembrane protein present on the
endoplasmic reticulum (ER) and the Golgi apparatus. Transcript
levels are low during growth and vary during development reaching
high levels during aggregation and late developmental stages. The
Arabidopsis ortholog was described as a G protein coupled
receptor (GPCR) for abscisic acid present at the plasma membrane
whereas the mammalian ortholog is a Golgi-associated anion
channel functioning as Golgi pH regulator. To probe its role in
D. discoideum we generated a strain lacking GPHR. The mutant had
different growth characteristics compared to the AX2 parent
strain and exhibited changes during late development and formed
abnormally shaped small slugs and fruiting bodies. An analysis
of development specific markers revealed that their expression
was disturbed. The distribution of the endoplasmic reticulum and
the Golgi was unaltered at the immunofluorescence level. Likewise,
their function did not appear to be impaired since membrane
proteins were properly processed and glycosylated. Also, changes
in the external pH were sensed by the ER as indicated by a pH
sensitive ER probe as in wild type.
Submitted by Angelika Ngel [noegel@uni-koeln.de]
----------------------------------------------------------------------
The Dictyostelium MAPK ERK1 is phosphorylated in a secondary
response to early developmental signaling
David J. Schwebs and Jeffrey A. Hadwiger*
Department of Microbiology and Molecular Genetics, Oklahoma State
University, 307 Life Sciences East, Stillwater, OK 74078 USA
Cellular Signaling, in press
Previous reports have suggested that the two mitogen-activated
protein kinases (MAPKs) in Dictyostelium discoideum, ERK1 and ERK2,
can be directly activated in response to external cAMP even though
these MAPKs play different roles in the developmental life cycle.
To better characterize MAPK regulation, the levels of phosphorylated
MAPKs were analyzed in response to external signals. Only ERK2 was
rapidly phosphorylated in response to the chemoattractants, cAMP and
folate. In contrast, the phosphorylation of ERK1 occurred as a
secondary or indirect response to these stimuli and this
phosphorylation was enhanced by cell-cell interactions, suggesting
that other external signals can activate ERK1. The phosphorylation
of ERK1 or ERK2 did not require the function of the other MAPK in
these responses. Folate stimulation of a chimeric population of
erk1- and galpha4- cells revealed that the phosphorylation of ERK1
could be mediated through an intercellular signal other than folate.
Loss of ERK1 function suppressed the developmental delay and the
deficiency in anterior cell localization associated with galpha5-
mutants suggesting that ERK1 function can be down regulated through
Galpha5 subunit-mediated signaling. However, no major changes in the
phosphorylation of ERK1 were observed in galpha5- cells suggesting
that the Galpha5 subunit signaling pathway does not regulate the
phosphorylation of ERK1. These findings suggest that the activation
of ERK1 occurs as a secondary response to chemoattractants and that
other cell-cell signaling mechanisms contribute to this activation.
Galpha5 subunit signaling can down regulate ERK1 function to promote
prestalk cell development but not through major changes to the level
of phosphorylated ERK1.
Submitted by Jeff Hadwiger [jeff.hadwiger@okstate.edu]
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[End dictyNews, volume 40, number 28]
