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dictyNews Volume 42 Number 16
dictyNews
Electronic Edition
Volume 42, number 16
July 1, 2016
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of dictyNews, the Dicty Reference database and other
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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 [furukawa@uga.edu]
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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 [steve.charette@bcm.ulaval.ca]
———————————————————————————————————————
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 [cssawai@mail.ecc.u-tokyo.ac.jp]
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[End dictyNews, volume 42, number 16]
