dictyNews
Electronic Edition
Volume 42, number 16
July 1, 2016

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Abstracts
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De novo actin polymerization is required for model Hirano body 
formation in Dictyostelium

Yun Dong, Sonbol Shahid-Salles, Dan Sherling, Nathan Fechheimer, 
Nathan Iyer, Lance Wells, Marcus Fechheimer, Ruth Furukawa


Biology Open, in press

Hirano bodies are eosinophilic, actin-rich inclusions found in 
autopsied brains in numerous neurodegenerative diseases. 
The mechanism of Hirano body formation is unknown. Mass 
spectrometry analysis was performed to identify proteins from 
partially purified model Hirano bodies from Dictyostelium. This 
analysis identified proteins primarily belonging to ribosomes, 
proteasomes, mitochondria, and cytoskeleton. Profilin, Arp/2/3, 
and WASH identified by mass spectrometry were found to colocalise 
with model Hirano bodies. Due to their roles in actin regulation, we 
selected these proteins for further investigation. Inhibition of the 
Arp2/3 complex by CK666 prevented formation of model Hirano 
bodies. Since Arp2/3 activation occurs via the WASH or WAVE 
complex, we next investigated how these proteins affect Hirano 
body formation. Whereas model Hirano bodies could form in WASH-
deficient cells, they failed to form in cells lacking HSPC300, a 
member of the WAVE complex. We identified other proteins 
required for Hirano body formation that include profilin and VASP, 
an actin nucleation factor. In the case of VASP, both its G- and 
F-actin binding domains were required for model Hirano body 
formation. Collectively, our results indicate that de novo actin 
polymerization is required to form model Hirano bodies. 


submitted by: Ruth Furukawa [[log in to unmask]]
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Identification of Proteins Associated with Multilamellar Bodies 
Produced by Dictyostelium discoideum.

Denoncourt AM, Paquet VE, Sedighi A, Charette SJ


PLoS One. 2016 Jun 24;11(6):e0158270. 
doi: 10.1371/journal.pone.0158270. eCollection 2016.

Dictyostelium discoideum amoebae produce and secrete 
multilamellar bodies (MLBs) when fed digestible bacteria. The aim
of the present study was to elucidate the proteic content of MLBs. 
The lipid composition of MLBs is mainly amoebal in origin, 
suggesting that MLB formation is a protozoa-driven process that 
could play a significant role in amoebal physiology. We identified four 
major proteins on purified MLBs using mass spectrometry in order 
to better understand the molecular mechanisms governing MLB
formation and, eventually, to elucidate the true function of MLBs. 
These proteins were SctA, PhoPQ, PonC and a protein containing a 
cytidine/deoxycytidylate deaminase (CDD) zinc-binding region. SctA 
is a component of pycnosomes, which are membranous materials that 
are continuously secreted by amoebae. The presence of SctA on MLBs 
was confirmed by immunofluorescence and Western blotting using a 
specific anti-SctA antibody. The CDD protein may be one of the proteins 
recognized by the H36 antibody, which was used as a MLB marker in a 
previous study. The function of the CDD protein is unknown. 
Immunofluorescence and flow cytometric analyses confirmed that the 
H36 antibody is a better marker of MLBs than the anti-SctA antibody. 
This study is an additional step to elucidate the potential role of MLBs 
and revealed that only a small set of proteins appeared to be present 
on MLBs.


submitted by: Steve Charette [[log in to unmask]]
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Self-organization of chemoattractant waves in Dictyostelium 
depends on F-actin and cell–substrate adhesion

Fumihito Fukujin, Akihiko Nakajima, Nao Shimada, Satoshi Sawai


J. Roy. Soc. Interface, 
http://dx.doi.org/10.1098/rsif.2016.0233

In the social amoeba Dictyostelium discoideum, travelling waves 
of extracellular cyclic adenosine monophosphate (cAMP) self-
organize in cell populations and direct aggregation of individual 
cells to form multicellular fruiting bodies. In contrast to the large 
body of studies that addressed how movement of cells is 
determined by spatial and temporal cues encoded in the dynamic 
cAMP gradients, how cell mechanics affect the formation of a 
self-generated chemoattractant field has received less attention. 
Here, we show, by live cell imaging analysis, that the periodicity 
of the synchronized cAMP waves increases in cells treated with 
the actin inhibitor latrunculin. Detail analysis of the extracellular 
cAMP-induced transients of cytosolic cAMP (cAMP relay response) 
in well-isolated cells demonstrated that their amplitude and duration 
were markedly reduced in latrunculin-treated cells. Similarly, in cells 
strongly adhered to a poly-L-lysine-coated surface, the response 
was suppressed, and the periodicity of the population-level 
oscillations was markedly lengthened. Our results suggest that 
cortical F-actin is dispensable for the basic low amplitude relay 
response but essential for its full amplification and that this enhanced 
response is necessary to establish high-frequency signalling centres. 
The observed F-actin dependence may prevent aggregation centres 
from establishing in microenvironments that are incompatible with 
cell migration.


submitted by: Satoshi Sarwai [[log in to unmask]]
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[End dictyNews, volume 42, number 16]