dictyNews
Electronic Edition
Volume 41, number 6
March 27, 2015
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Abstracts
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Concurrent co-evolution of intra-organismal cheaters and resisters
Levin, Samuel; Brock, Debra; Queller, David; Strassmann, Joan
Journal of Evolutionary Biology, in press
The evolution of multicellularity is a major transition that is not
yet fully understood. Specifically, we do not know if there are any
mechanisms by which multicellularity can be maintained without a
single cell bottleneck or other relatedness enhancing mechanisms.
Under low relatedness, cheaters can evolve that benefit from the
altruistic behaviour of others without themselves sacrificing. If
these are obligate cheaters, incapable of co-operating, their spread
can lead to the demise of multicellularity. One possibility, however,
is that co-operators can evolve resistance to cheaters. We tested
this idea in a facultatively multicellular social amoeba,
Dictyostelium discoideum. This amoeba usually exists as a single
cell but, when stressed, thousands of cells aggregate to form a
multicellular organism in which some of the cells sacrifice for the
good of others. We used lineages that had undergone experimental
evolution at very low relatedness, during which time obligate
cheaters evolved. Unlike earlier experiments, which found resistance
to cheaters that were prevented from evolving, we competed cheaters
and non-cheaters that evolved together, and cheaters with their
ancestors. We found that non-cheaters can evolve resistance to
cheating before cheating sweeps through the population and
multicellularity is lost. Our results provide insight into cheater-
resister co-evolutionary dynamics, in turn providing experimental
evidence for the maintenance of at least a simple form of
multicellularity by means other than high relatedness.
Submitted by Samuel Levin [[log in to unmask]]
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Lipid Droplet Dynamics at Early Stages of Mycobacterium marinum
Infection in Dictyostelium
Caroline Barisch1, Peggy Paschke2, Monica Hagedorn3, Markus
Maniak2 and Thierry Soldati1*
1Department of Biochemistry, Science II, University of Geneva,
30 quai Ernest-Ansermet, 1211 Geneva-4, Switzerland
2Department of Cell Biology, University of Kassel,
Heinrich-Plett-Str. 40, 34132 Kassel, Germany
3Section Parasitology, Bernhard Nocht Institute for Tropical
Medicine, Bernhard-Nocht-Straße 74, 20359 Hamburg, Germany
Cellular Microbiology, in press
Lipid droplets exist in virtually every cell type, ranging from
mammals to plants, but also to eukaryotic and prokaryotic unicellular
organisms such as Dictyostelium and bacteria. They serve amongst
other roles as energy reservoir that cells consume in times of
starvation. Mycobacteria and some other intracellular pathogens
hijack these organelles as a nutrient source and to build up their
own lipid inclusions. The mechanisms by which host lipid droplets
are captured by the pathogenic bacteria is extremely poorly understood.
Using the powerful Dictyostelium discoideum / Mycobacterium marinum
infection model we observed that, immediately after their uptake,
lipid droplets translocate to the vicinity of the vacuole containing
live but not dead mycobacteria. Induction of lipid droplets in
Dictyostelium prior to infection resulted in a vast accumulation of
neutral lipids and sterols inside the bacterium-containing compartment.
Subsequently, under these conditions, mycobacteria accumulated much
larger lipid inclusions. Strikingly, the Dictyostelium homologue of
perilipin and the murine perilipin 2 surrounded bacteria that had
escaped to the cytosol of Dictyostelium or microglial BV-2 cells,
respectively. Moreover, bacterial growth was inhibited in
Dictyostelium plnA knockout cells. In summary, our results provide
evidence that mycobacteria actively manipulate the lipid metabolism
of the host from very early infection stages.
Submitted by Thierry Soldati [[log in to unmask]]
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Live Imaging of Mycobacterium marinum Infection in Dictyostelium
discoideum
Caroline Barisch, Ana T. López-Jiménez, and Thierry Soldati
Department of Biochemistry, Science II, University of Geneva,
30 quai Ernest-Ansermet, 1211 Geneva-4, Switzerland
Methods Mol Biol. 2015;1285:369-85.
The pdf file of the chapter is available upon request
The Dictyostelium discoideum–Mycobacterium marinum host–
pathogen system is a recently established and powerful model
system for mycobacterial infection. In this chapter, two simple
protocols for live imaging of Dictyostelium discoideum infection are
described. The first method is used to monitor the dynamics of
recruitment of GFP-tagged Dictyostelium discoideum proteins at single
time-points corresponding to the main stages of the infection (1.5–72 h
post infection). The second method focuses at the early stages of the
establishment of an infection (0–3 h post infection). In addition,
several procedures to improve the imaging of the bacterium-containing
compartment are described. Basic bacterial parameters such as
bacterial growth and the recruitment of host proteins to the
bacterium-containing compartment can be easily and precisely
quantified using macros for ImageJ. These methods can be adapted to
monitoring mycobacteria infection in other systems using mammalian
cells.
Submitted by Thierry Soldati [[log in to unmask]]
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[End dictyNews, volume 41, number 6]
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