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dictyNews Volume 41 Number 01
dictyNews
Electronic Edition
Volume 41, number 1
January 9, 2015
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.
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Abstracts
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Evidence for nucleolar subcompartments in Dictyostelium
Andrew Catalano (a) and Danton H. OÕDay (a,b)*
a Department of Biology, University of Toronto at Mississauga,
3359 Mississauga rd. N., Mississauga, Ontario, Canada, L5L 1C6
b Department of Cell and Systems Biology, University of Toronto,
25 Harbord st., Toronto, Ontario, Canada, M5S 3G5
Biochemical Biophysical Research Communications, in press
Free online: http://authors.elsevier.com/sd/article/S0006291X14022165
The nucleolus is a multifunctional nuclear compartment usually
consisting of two to three subcompartments which represent stages
of ribosomal biogenesis. It is linked to several human diseases
including viral infections, cancer, and neurodegeneration.
Dictyostelium is a model eukaryote for the study of fundamental
biological processes as well as several human diseases however
comparatively little is known about its nucleolus. Unlike most
nucleoli it does not possess visible subcompartments at the
ultrastructural level. Several recently identified nucleolar
proteins in Dictyostelium leave the nucleolus after treatment with
the rDNA transcription inhibitor actinomycin-D (AM-D). Different
proteins exit in different ways, suggesting that previously
unidentified nucleolar subcompartments may exist. The identification
of nucleolar subcompartments would help to better understand the
nucleolus in this model eukaryote. Here, we show that Dictyostelium
nucleolar proteins nucleomorphin isoform NumA1 and Bud31 localize
throughout the entire nucleolus while calcium-binding protein 4a
localizes to only a portion, representing nucleolar subcompartment
1 (NoSC1). SWI/SNF complex member Snf12 localizes to a smaller area
within NoSC1 representing a second nucleolar subcompartment, NoSC2.
The nuclear/nucleolar localization signal KRKR from Snf12 localized
GFP to NoSC2, and thus also appears to function as a nucleolar
subcompartment localization signal. FhkA localizes to the nucleolar
periphery displaying a similar pattern to that of Hsp32. Similarities
between the redistribution patterns of Dictyostelium nucleolar
proteins during nucleolar disruption as a result of either AM-D
treatment or mitosis support these subcompartments. A model for the
AM-D-induced redistribution patterns is proposed.
Submitted by: Danton H. OÕDay: danton.oday@utoronto.ca
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Partial genetic suppression of a loss of function mutant of the
Neuronal Ceroid Lipofuscinosis-associated protease TPP1 in
Dictyostelium discoideum
Jonathan E. Phillips and Richard H. Gomer
Disease Models & Mechanisms, in press
Neuronal Ceroid Lipofuscinosis (NCL) is the most common childhood-
onset neurodegenerative disease. NCL is inevitably fatal, and there
is no current treatment. Children with NCL show progressive decline
in movement, vision, and mental abilities and accumulation of
autofluorescent deposits in neurons and other cell types. Late-
infantile NCL is caused by mutations in the lysosomal protease
tripeptdyl peptidase 1 (TPP1). TPP1 cleaves tripeptides from the
N-terminus of proteins in vitro, but little is known about the
physiological function of TPP1. TPP1 shows wide conservation in
vertebrates but is not found in Drosophila, C. elegans, or
S. cerevisiae. Here, we characterize ddTpp1, a TPP1 ortholog present
in the social amoeba Dictyostelium discoideum. Lysates from cells
lacking ddTpp1 show reduced but not abolished ability to cleave a
TPP1 substrate, suggesting that other Dictyostelium enzymes can
perform this cleavage. ddTpp1 and human TPP1 localize to the
lysosome in Dictyostelium, indicating conserved function and
trafficking. Cells lacking ddTpp1 show precocious multicellular
development and a reduced ability to form spores during development.
When cultured in autophagy-stimulating conditions, cells lacking
ddTpp1 rapidly decrease in size and are less viable than wild-type
cells, suggesting that one function of ddTpp1 may be to limit
autophagy. Cells lacking ddTpp1 show strongly impaired development
in the presence of the lysosome-perturbing drug chloroquine, and
this phenotype can be suppressed by a secondary mutation in the gene
stpA, which encodes a protein with some similarity to mammalian
oxysterol-binding proteins (OSBPs). Together, these results suggest
that targeting specific proteins may be a viable way to suppress the
effects of loss of TPP1 function.
Submitted by Richard Gomer [rgomer@tamu.edu]
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Compact Halo-Ligand-Conjugated Quantum Dots for Multicolored
Single-Molecule Imaging of Overcrowding GPCR Proteins on Cell
Membranes.
Akihito Komatsuzaki, Tatsuya Ohyanagi, Yoshikazu Tsukasaki,
Yukihiro Miyanaga, Masahiro Ueda, and Takashi Jin
Small. 2014 Dec 12.
doi: 10.1002/smll.201402508.
http://onlinelibrary.wiley.com/doi/10.1002/smll.201402508/abstract
To detect single molecules within the optical diffraction limit
(< ca. 200 nm), a multicolored imaging technique is developed using
Halo-ligand conjugated quantum dots (Halo-QDs; <6 nm in diameter).
Using three types of Halo-QDs, multicolored single-molecule
fluorescence imaging of GPCR proteins in Dictyostelium cells is
achieved.
Submitted by Yukihiro Miyanaga [miyang@bio.sci.osaka-u.ac.jp]
----------------------------------------------------------------------
Surcel A, Ng W-P, West-Foyle H, Zhu Q, Ren Y, Avery L, Krenc AK,
Meyers D, Rock RS, Anders RA, Freel Meyers C, Robinson DN.
Pharmacological activation of myosin II paralogs to correct cell
mechanics defects.
Proc. Natl. Acad. Sci. USA 2015, in press
Current approaches to cancer treatment focus on targeting signal
transduction pathways. Here, we develop an alternative system for
targeting cell mechanics for the discovery of novel therapeutics.
We designed a live-cell, high-throughput chemical screen to
identify mechanical modulators. We characterized
4-hydroxyacetophenone (4-HAP), which enhances the cortical
localization of the mechanoenzyme myosin II, independent of myosin
heavy-chain phosphorylation, thus increasing cellular cortical
tension. To shift cell mechanics, 4-HAP requires myosin II,
including its full power stroke, specifically activating human
MYH10 and MYH14, but not MYH9. We further demonstrated that
invasive pancreatic cancer cells are more deformable than normal
pancreatic ductal epithelial cells, a mechanical profile that was
partially corrected with 4-HAP, which also decreased the invasion
and migration of these cancer cells. Overall, 4-HAP modifies
nonmuscle myosin II-based cell mechanics across phylogeny and
disease states and provides proof-of-concept that cell mechanics
offers a rich drug target space, allowing for possible corrective
modulation of tumor cell behavior.
Submitted by Doug Robinson [dnr@jhmi.edu]
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[End dictyNews, volume 41, number 1]
