dictyNews
Electronic Edition
Volume 40, number 28
November 07, 2014

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Abstracts
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Article for the “Free-living amoebae Special Issue”: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 [[log in to unmask]]
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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 [[log in to unmask]]
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Deckstein, J., van Appeldorn, J., Tsangarides, M., Yiannakou, 
K., Müller, 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 Nögel [[log in to unmask]]
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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 [[log in to unmask]]   
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[End dictyNews, volume 40, number 28]