dictyNews
Electronic Edition
Volume 40, number 11
April 18, 2014
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Abstracts
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Tianzhi Luo, Vasudha Srivastava, Yixin Ren, Douglas N. Robinson
Mimicking the mechanical properties of the cell cortex by the
self-assembly of an actin cortex in vesicles.
App. Phys. Lett. 2014, in press
The composite of the actin cytoskeleton and plasma membrane plays
important roles in many biological events. Here, we employed the
emulsion method to synthesize artificial cells with biomimetic actin
cortex in vesicles and characterized their mechanical properties. We
demonstrated that the emulsion method provides the flexibility to adjust
the lipid composition and protein concentrations in artificial cells to
achieve the desired size distribution, internal microstructure and
mechanical properties. Moreover, comparison of the cortical elasticity
measured for reconstituted artificial cells to that of real cells, including
those manipulated using genetic depletion and pharmacological
inhibition, strongly supports that actin cytoskeletal proteins are
dominant over lipid molecules in cortical mechanics. Our study
indicates that the assembly of biological systems in artificial cells with
purified cellular components provides a powerful way to answer
biological questions.
Submitted by Douglas Robinson [[log in to unmask]]
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Cell signaling during development of Dictyostelium
William F. Loomis
Cell and Developmental Biology, University of California San Diego
La Jolla, CA 92093
Developmental Biology, in press
Review
Continuous communication between cells is necessary for
development of any multicellular organism and depends on the
recognition of secreted signals. A wide range of molecules
including proteins, peptides, amino acids, nucleic acids, steroids
and polylketides are used as intercellular signals in plants and
animals. They are also used for communication in the social
amoeba Dictyostelium discoideum when the solitary cells
aggregate to form multicellular structures. Many of the signals
are recognized by surface receptors that are seven-
transmembrane proteins coupled to trimeric G proteins, which
pass the signal on to components within the cytoplasm.
Dictyostelium cells have to judge when sufficient cell density
has been reached to warrant transition from growth to
differentiation. They have to recognize when exogenous nutrients
become limiting, and then synchronously initiate development. A
few hours later they signal each other with pulses of cAMP that
regulate gene expression as well as direct chemotactic
aggregation. They then have to recognize kinship and only
continue developing when they are surrounded by close kin.
Thereafter, the cells diverge into two specialized cell types,
prespore and prestalk cells, that continue to signal each other in
complex ways to form well proportioned fruiting bodies. In this way
they can proceed through the stages of a dependent sequence in
an orderly manner without cells being left out or directed down
the wrong path.
Submitted by Bill Loomis [[log in to unmask]]
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TSET: an ancient and widespread membrane trafficking complex
Jennifer Hirst1§*, Alexander Schlacht2§, John P. Norcott3+, David
Traynor4+, Gareth Bloomfield4, Robin Antrobus1, Robert R. Kay4,
Joel B. Dacks2*, and Margaret S. Robinson1*
1University of Cambridge, Cambridge Institute for Medical Research,
Cambridge, UK
2Department of Cell Biology, University of Alberta, Edmonton, Canada
3University of Cambridge, Department of Engineering, Cambridge, UK
4MRC Laboratory of Molecular Biology, Cambridge, UK
eLife, in press
The heterotetrameric AP and F-COPI complexes help to define the
cellular map of modern eukaryotes. To search for related machinery,
we developed a structure-based bioinformatics tool, and identified
the core subunits of TSET, a “missing link” between the APs and
COPI. Studies in Dictyostelium indicate that TSET is a heterohexamer,
with two associated scaffolding proteins. TSET is non-essential in
Dictyostelium, but may act in plasma membrane turnover, and is
essentially identical to the recently described TPLATE complex, TPC.
However, whereas TPC was reported to be plant-specific, we can
identify a full or partial complex in every eukaryotic supergroup. An
evolutionary path can be deduced from the earliest origins of the
heterotetramer/scaffold coat to its multiple manifestations in modern
organisms, including the mammalian muniscins, descendants of the
TSET medium subunits. Thus, we have uncovered the machinery for
an ancient and widespread pathway, which provides new insights into
early eukaryotic evolution.
Submitted by Rob Kay [[log in to unmask]]
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Calcineurin-Crz1 signaling in lower eukaryotes.
Thewes S
Eukaryotic Cell, in press
Review
Calcium ions are ubiquitous intracellular messengers. An increase in
the cytosolic Ca2+ concentration activates many proteins including
calmodulin and the Ca2+/calmodulin-dependent protein phosphatase
calcineurin. The phosphatase is conserved from yeast to man (except
plants) and many target proteins of calcineurin have been identified.
The most prominent and best-investigated targets, however, are the
transcription factors NFAT (nuclear factor of activated T-cells) in
mammals and Crz1 (calcineurin responsive zinc finger 1) in yeast. In
recent years many orthologues of Crz1 have been identified and
characterized in various fungi, amoebae and other lower eukaryotes.
It has been shown that the functions of calcineurin-Crz1 signaling are
conserved in the different organisms ranging from ion homeostasis,
through cell wall biogenesis, to the building of filamentous structures.
Furthermore frequency-modulated gene expression through Crz1 has
been discovered as a striking new mechanism by which cells can
coordinate their response to a signal. In this review I will focus on the
latest findings concerning calcineurin-Crz1 signaling in fungi, amoebae
and other lower eukaryotes. I will discuss the potential of Crz1 and its
orthologues as putative drug targets and I will also discuss possible
parallels with calcineurin-NFAT signaling in mammals.
Submitted by Sascha Thewes [[log in to unmask]]
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[End dictyNews, volume 40, number 11]
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