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dictyNews Volume 38 Number 22
dictyNews
Electronic Edition
Volume 38, number 22
August 31, 2012
Please submit abstracts of your papers as soon as they have been
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or by using the form at
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Abstracts
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The Nramp (Slc11) proteins regulate development, resistance to
pathogenic bacteria and iron homeostasis in Dictyostelium discoideum
Barbara Peracino, Simona Buracco and Salvatore Bozzaro*
Department of Clinical and Biological Sciences, University of Turin,
AOU S. Luigi, 10043 Orbassano, Italy
J. Cell Sci,. in press
The Dictyostelium discoideum genome harbours two genes encoding
members of the Nramp superfamily, which is conserved from bacteria
(MntH proteins) to humans (Slc11 proteins). Nramps are proton-driven
metal ion transporters with a preference for iron and manganese.
Acquisition of these metal cations is vital for all cells, as they act as
redox cofactors and regulate key cellular processes, such as DNA
synthesis, electron transport, energy metabolism and oxidative stress.
Dictyostelium Nramp1 (Slc11a1), like its mammalian ortholog, mediates
resistance to infection by invasive bacteria. We have extended the
analysis to the nramp2 gene, by generating single and double
nramp1/nramp2 knockout mutants and cells expressing GFP fusion
proteins. In contrast to Nramp1, which is recruited to phagosomes and
macropinosomes, the Nramp2 protein is localized exclusively in the
membrane of the contractile vacuole, a vesicular-tubular network
regulating cellular osmolarity. Both proteins colocalize with the
V-H+ ATPase, which can provide the electrogenic force for vectorial
transport. Like nramp1, nramp2 gene disruption affects resistance to
Legionella pneumophila. Disrupting both genes additionally leads to
defects in development, with strong delay in cell aggregation, formation
of large streams and multi-tipped aggregates. Single and double mutants
display differential sensitivity to cell growth under conditions of iron
overload or depletion. The data favour the hypothesis that Nramp1 and
Nramp2, under control of the V-H+ ATPase, synergistically regulate iron
homeostasis, with the contractile vacuole possibly acting as a store for
metal cations.
Submitted by Salvatore Bozzaro [salvatore.bozzaro@unito.it]
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Regulation of multiple tip formation by caffeine in cellular
slime molds
Pundrik Jaiswal, Shashi Prakash Singh, Prasad Aiyar,
Rakhil Akkali and Ramamurthy Baskar
BMC Development Biology 2012, 12:26
Background
The multicellular slug in Dictyostelium has a single tip that acts as
an organising centre patterning the rest of the slug. High adenosine
levels at the tip are believed to be responsible for this tip dominance
and the adenosine antagonist, caffeine overrides this dominance
promoting multiple tip formation.
Results
Caffeine induced multiple tip effect is conserved in all the Dictyostelids
tested. Two key components of cAMP relay namely, cAMP
phosphodiesterase (Pde4) and adenyl cyclase-A (AcaA) levels get
reduced during secondary tip formation in Dictyostelium discoideum.
Pharmacological inhibition of cAMP phosphodiesterase also resulted
in multiple tips. Caffeine reduces cAMP levels by 16.4, 2.34, 4.71 and
6.30 folds, respectively in D. discoideum, D. aureostipes, D. minutum
and Polysphondylium pallidum. We propose that altered cAMP levels,
perturbed cAMP gradient and impaired signalling may be the critical
factors for the origin of multiple tips in other Dictyostelids as well. In
the presence of caffeine, slug cell movement gets impaired and
restricted. The cell type specific markers, ecmA (prestalk) and pspA
(prespore) cells are not equally contributing during additional tip
formation. During additional tip emergence, prespore cells
transdifferentiate to compensate the loss of prestalk cells.
Conclusion
Caffeine decreases adenyl cyclase--A (AcaA) levels and as a
consequence low cAMP is synthesised altering the gradient. Further
if cAMP phosphodiesterase (Pde4) levels go down in the presence
of caffeine, the cAMP gradient breaks down. When there is no cAMP
gradient, directional movement is inhibited and might favour
re-differentiation of prespore to prestalk cells.
Submitted by Pundrik Jaiswal [pundrik_jaiswal@yahoo.co.in]
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[End dictyNews, volume 38, number 22]
