dictyNews
Electronic Edition
Volume 46, number 15
May 29, 2020
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Abstracts
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Cell-substrate adhesion drives Scar/WAVE activation and phosphorylation,
which controls pseudopod lifetime
Shashi Prakash Singh, Peter A. Thomason, Sergio Lilla, Matthias Schaks,
Qing Tang, Bruce L. Goode, Laura M. Machesky, Klemens Rottner,
Robert H. Insall
PLOS Biology, accepted
The Scar/WAVE complex is the principal catalyst of pseudopod and
lamellipod formation. Here we show that Scar/WAVE’s proline-rich domain
is polyphosphorylated after the complex is activated. Blocking Scar/WAVE
activation stops phosphorylation in both Dictyostelium and mammalian cells,
implying that phosphorylation modulates pseudopods after they have been
formed, rather than controlling whether they are initiated. Unexpectedly,
phosphorylation is not promoted by chemotactic signalling, but is greatly
stimulated by cell:substrate adhesion and diminished when cells deadhere.
Phosphorylation-deficient or phosphomimetic Scar/WAVE mutants are both
normally functional, and rescue the phenotype of knockout cells,
demonstrating that phosphorylation is dispensable for activation and actin
regulation. However, pseudopods and patches of phosphorylation-deficient
Scar/WAVE last substantially longer in mutants, altering the dynamics and
size of pseudopods and lamellipods, and thus changing migration speed.
Scar/WAVE phosphorylation does not require ERK2, but the MAPKKK
homologue SepA contributes substantially - sepA mutants have less steady-
state phosphorylation, which does not increase in response to adhesion.
The mutants also behave similarly to cells expressing phosphorylation-
deficient Scar, with longer-lived pseudopods and patches of Scar recruitment.
We conclude that pseudopod engagement with substratum is more important
than extracellular signals at regulating Scar/WAVE’s activity, and that
phosphorylation acts as a pseudopod timer, by promoting Scar/WAVE
turnover.
submitted by: Robert Insall [[log in to unmask]]
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Conidial Melanin of the Human-Pathogenic Fungus Aspergillus
fumigatus Disrupts Cell Autonomous Defenses in Amoebae
Iuliia Ferling, Joe Dan Dunn, Alexander Ferling, Thierry Soldati,
Falk Hillmann
https://mbio.asm.org/content/11/3/e00862-20
DOI: 10.1128/mBio.00862-20
The human-pathogenic fungus Aspergillus fumigatus is a ubiquitous
saprophyte that causes fatal lung infections in immunocompromised
individuals. Following inhalation, conidia are ingested by innate immune cells
and can arrest phagolysosome maturation. How this virulence trait could have
been selected for in natural environments is unknown. Here, we found that
surface exposure of the green pigment 1,8-dihydroxynaphthalene-(DHN)-
melanin can protect conidia from phagocytic uptake and intracellular killing by
the fungivorous amoeba Protostelium aurantium and delays its exocytosis from
the nonfungivorous species Dictyostelium discoideum. To elucidate the
antiphagocytic properties of the surface pigment, we followed the antagonistic
interactions of A. fumigatus conidia with the amoebae in real time. For both
amoebae, conidia covered with DHN-melanin were internalized at far lower
rates than were seen with conidia lacking the pigment, despite high rates of
initial attachment to nonkilling D. discoideum. When ingested by D. discoideum,
the formation of nascent phagosomes was followed by transient acidification of
phagolysosomes, their subsequent neutralization, and, finally, exocytosis of the
conidia. While the cycle was completed in less than 1 h for unpigmented
conidia, the process was significantly prolonged for conidia covered with DHN-
melanin, leading to an extended intracellular residence time. At later stages of
this cellular infection, pigmented conidia induced enhanced damage to
phagolysosomes and infected amoebae failed to recruit the ESCRT (endosomal
sorting complex required for transport) membrane repair machinery or the
canonical autophagy pathway to defend against the pathogen, thus promoting
prolonged intracellular persistence in the host cell and the establishment of a
germination niche in this environmental phagocyte.
submitted by: Falk Hillmann [[log in to unmask]]
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Cytokinins in Dictyostelia – A unique model for studying the functions of
signaling agents from species to kingdoms
Megan M. Aoki1*, R. J. N. Emery1, Christophe Anjard2,3,4, Craig R. Brunetti1,
Robert J. Huber1
1 - Department of Biology, Trent University, Peterborough, Ontario, Canada
2 - UMR5306 Institut Lumière Matière (ILM), France
3 - Université Claude Bernard Lyon 1, France
4 - Université de Lyon, France
Frontiers in Cell and Developmental Biology, accepted
Cytokinins (CKs) are a diverse group of evolutionarily significant growth-
regulating molecules. While the CK biosynthesis and signaltransduction
pathways are the most well-understood in plant systems, these molecules have
been identified in all kingdoms of life.This review follows the recent discovery
of an expanded CK profile in the social amoeba, Dictyostelium discoideum. A
comprehensive review on the present knowledge of CK biosynthesis, signal
transduction, and CK-small molecule interactions within members of
Dictyostelia will be summarized. In doing so, the utility of social amoebae will
be highlighted as a model system for studying the evolution of these hormone-
like signaling agents, which will set the stage for future research in this area.
submitted by: Megan Aoki [[log in to unmask]]
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[End dictyNews, volume 46, number 15]
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