dictyNews
Electronic Edition
Volume 40, number 20
August 22, 2014
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Abstracts
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Huntingtin supplies a csaA-independent function essential for
EDTA-resistant homotypic cell adhesion in Dictyostelium discoideum
Morgan N. Thompson, Marcy E. MacDonald, James F. Gusella
and Michael A. Myre
Center for Human Genetic Research, Massachusetts General Hospital,
Harvard Medical School. Boston, MA, 02114 USA
The Journal of Huntington’s Disease, in press
Background: The CAG triplet repeat expansion mutation in the HTT locus,
which results in neurodegeneration in Huntington’s disease, elongates a
polyglutamine tract in huntingtin, a HEAT/HEAT-like protein that has been
highly structurally conserved through evolution. In several organisms,
huntingtin is necessary for proper cell-cell adhesion and normal development.
Objective: Dictyostelium discoideum huntingtin null (htt-) cells
display a variety of developmental abnormalities and completely fail to
acquire EDTA-resistant homotypic cell adhesion during starvation in
suspension culture.
Methods: Here, we have assessed the hypothesis that Htt may be a genetic
interactor of csaA, a major regulator of EDTA-resistant homotypic cell
adhesion in D. discoideum. Immunoblot analysis demonstrated that csaA
protein expression is dysregulated in htt- cells.
Results: Unexpectedly, csaA overexpression, previously shown to rescue
csaA- cell adhesion, failed to rescue the htt- adhesion defect. Thus,
while htt was required for proper expression of the csaA protein, csaA
overexpression was not sufficient to confer EDTA-resistant adhesion in
the context of the htt- genetic background in contrast to parental cells.
This implies a novel role for Htt in conferring csaA-dependent, EDTA-
resistant cell adhesion that warrants further investigation. Calcium
supplementation restored both endogenous csaA protein levels and
EDTA-resistant adhesion in htt- cells.
Conclusions: Our data suggests the existence of an additional mechanism
that overcomes the EDTA-resistant adhesion defect of htt- cells in the early
development of D. discoideum.
Submitted by Michael Myre [[log in to unmask]]
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Huntingtin Regulates Ca2+ Chemotaxis and K+-facilitated cAMP Chemotaxis,
in Conjunction with the Monovalent Cation/H+ Exchanger Nhe1, in a Model
Developmental System: Insights into its Possible Role in Huntington's Disease
Deborah Wessels, Daniel F. Lusche, Amanda Scherer, Spencer Kuhl,
Michael A. Myre* and David Soll
Developmental Studies Hybridoma Bank, Department of Biology,
University of Iowa, Iowa City, Iowa 52242;
*Center for Human Genetic Research, Massachusetts General Hospital,
Boston, Harvard Medical School, Boston MA, 02114 USA
Developmental Biology, in press.
Huntington’s disease is a neurodegenerative disorder, attributable to an
expanded trinucleotide repeat in the coding region of the human HTT gene,
which encodes the protein huntingtin. These mutations lead to huntingtin
fragment inclusions in the striatum of the brain. However, the exact function
of normal huntingtin and the defect causing the disease remain obscure.
Because there are indications that huntingtin plays a role in Ca2+ homeostasis,
we studied the deletion mutant of the HTT ortholog in the model developmental
system Dictyostelium discoideum, in which Ca2+ plays a role in receptor-
regulated behavior related to the aggregation process that leads to multicellular
morphogenesis. In D.discoideum, the htt- mutant failed to undergo both
K+-facilitated chemotaxis in spatial gradients of the major chemoattractant
cAMP, and chemotaxis up a spatial gradient of Ca2+, but behaved normally in
Ca2+-facilitated cAMP chemotaxis and Ca2+-dependent flow-directed motility.
This was the same phenotypic profile of the null mutant of Nhel, a monovalent
cation/H+exchanger. The htt- mutant also failed to orient correctly during natural
aggregation, as was the case for the Nhel mutant. Moreover, in a K+-based
buffer the normal localization of actin was similarly defective in both htt- and
nhe1- cells in a K+-based buffer, and the normal localization of Nhe1 was
disrupted in the htt- mutant. These observations demonstrate that Htt and
Nhel play roles in the same specific cation-facilitated behaviors and that Nhel
localization is directly or indirectly regulated by Htt. Similar cation-dependent
behaviors and a similar relationship between Htt and Nhe1 have not been
reported for mammalian neurons and deserves investigation, especially as it
may relate to Huntington’s disease.
Submitted by Michael Myre [[log in to unmask]]
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A cyanobacterial light activated adenylylcyclase partially restores
development of a Dictyostelium Discoideum, adenylyl cyclase A null mutant
Zhi-hui Chen1, Sarah Raffelberg2, Aba Losi3, Pauline Schaap1* ,
Wolfgang Gärtner2*
1 College of Life Sciences, University of Dundee, Dundee UK
2 MPI Chemical Energy Conversion, Mülheim, Germany
3 Dept. of Physics and Earth Sciences, University of Parma, Parma, Italy
*to whom correspondence should be addressed:
[log in to unmask]; [log in to unmask]
Journal of Biotechnology, in press
Abstract: A light-regulated adenylyl cyclase, mPAC, was previously identified
from the cyanobacterium Microcoleus chthonoplastes PCC7420. MPAC
consists of a flavin-based blue light-sensing LOV domain and a catalytic
domain. In this work, we expressed mPAC in an adenylate cyclase A null
mutant (aca-) of the eukaryote Dictyostelium discoideum and tested to what
extent light activation of mPAC could restore the cAMP-dependent
developmental programme of this organism. Amoebas of Dictyostelium, a well-
established model organism, generate and respond to cAMP pulses, which
cause them to aggregate and construct fruiting bodies. mPAC was expressed
under control of a constitutive actin-15 promoter in D. discoideum and displayed
low basal adenylyl cyclase activity in darkness that was about five-fold stimulated
by blue light. mPAC expression in aca- cells marginally restored aggregation and
fruiting body formation in darkness. However, more and larger fruiting bodies
were formed when mPAC expressing cells were incubated in light. Extending
former applications of light-regulated AC, these results demonstrate that mPAC
can be used to manipulate multicellular development in eukaryotes in a light
dependent manner.
Submitted by Zhihui Chen [[log in to unmask]]
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Two Dictyostelium Tyrosine Kinase-Like kinases function
in parallel, stress-induced STAT activation pathways
Tsuyoshi Araki*, Linh Hai Vu†, Norimitsu Sasaki‡, Takefumi Kawata‡,
Ludwig Eichinger† and Jeffrey G. Williams*§
* College of Life Sciences, Welcome Trust Biocentre, University of Dundee,
Dow St., Dundee, DD1 5EH, UK
† Center for Biochemistry Institute of Biochemistry I Joseph-Stelzmann-Str. 52
50931 Cologne Germany
‡ Department of Biology, Faculty of Science, Toho University, 2-2-1 Miyama,
Funabashi, Chiba 274-8510, Japan
§ [log in to unmask]
Molecular Biology of the Cell,, in press
When Dictyostelium cells are hyper-osmotically stressed STATc is activated
by tyrosine phosphorylation. Unusually, activation is regulated by serine
phosphorylation and consequent inhibition of a tyrosine phosphatase: PTP3.
The identity of the cognate tyrosine kinase is unknown and we show that two
Tyrosine Kinase-Like (TKL) enzymes, Pyk2 and Pyk3, share this function;
thus for stress-induced STATc activation, single null mutants are only
marginally impaired but the double mutant is non-activatable. When cells are
stressed Pyk2 and Pyk3 undergo increased auto-catalytic tyrosine
phosphorylation. The site(s) that are generated bind the SH2 domain of
STATc and then STATc becomes the target of further kinase action. The
signalling pathways that activate Pyk2 and Pyk3 are only partially overlapping
and there may be a structural basis for this difference because Pyk3 contains
both a TKL domain and a pseudokinase domain. The latter functions, like the
JH2 domain of metazoan JAKs, as a negative regulator of the kinase domain.
The fact that two differently regulated kinases catalyse the same
phosphorylation event may facilitate specific targeting because under stress
Pyk3 and Pyk2 accumulate in different parts of the cell; Pyk3 moves from the
cytosol to the cortex while Pyk2 accumulates in cytosolic granules that
co-localise with PTP3.
The University of Dundee is a registered Scottish Charity, No: SC015096
Submitted by Jeff Williams [[log in to unmask]]
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Dictyostelium uses ether-linked inositol phospholipids for
intracellular signalling
Jonathan Clark, Robert R Kay, Anna Kielkowska, Izabella Niewczas,
Louise Fets, David Oxley, Len R Stephens, Phillip T Hawkins
Signalling Programme and Babraham Biosciences Technology,
Babraham Research Campus, Babraham, Cambridge, CB22 3AT, UK.
MRC Laboratory of Molecular Biology, Francis Crick Avenue,
Cambridge Biomedical Campus, Cambridge CB2 0QH, UK
Authors for correspondence: Rob Kay, Len Stephens and Phillip Hawkins
EMBO J, in press
Inositol phospholipids are critical regulators of membrane biology throughout
eukaryotes. The general principle by which they perform these roles is
conserved across species and involves binding of differentially phosphorylated
inositol headgroups to specific protein domains. This interaction serves to both
recruit and regulate the activity of several different classes of protein which act
on membrane surfaces. In mammalian cells, these phosphorylated inositol
headgroups are predominantly borne by a C38:4 diacyl glycerol backbone.
We show here that the inositol phospholipids of Dictyostelium are different,
being highly enriched in an unusual C34:1e lipid backbone,
1- hexadecyl -2-(11Z-octadecenoyl)-sn-glycero-3-phospho-(1'-myo-inositol),
in which the sn-1 position contains an ether-linked C16:0 chain; they are thus
plasmanylinositols. These plasmanylinositols respond acutely to stimulation
of cells with chemoattractants and their levels are regulated by PIPKs, PI3Ks
and PTEN. In mammals and now in Dictyostelium, the hydrocarbon chains
of inositol phospholipids are a highly selected subset of those available to
other phospholipids, suggesting that different molecular selectors are at play
in these organisms but serve a common, evolutionary conserved purpose.
Submitted by Rob Kay [[log in to unmask]]
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Evolutionary reconstruction of pattern formation in 98 Dictyostelium species
reveals that cell-type specialization by lateral inhibition is a derived trait
Christina Schilde, Anna Skiba and Pauline Schaap
College of Life Sciences, University of Dundee, UK
EvoDevo, in press
Multicellularity provides organisms with opportunities for cell-type
specialization, but requires novel mechanisms to position correct proportions
of different cell types throughout the organism. Dictyostelid social amoebas
display an early form of multicellularity, where amoebas aggregate to form
fruiting bodies, which contain only spores or up to four additional cell-types.
These cell types will form the stalk and support structures for the stalk and
spore head. Phylogenetic inference subdivides Dictyostelia into four major
groups, with the model organism D.discoideum residing in group 4.
Differentiation of its five cell types is dominated in D.discoideum by lateral
inhibition-type mechanisms that trigger scattered cell differentiation, with
tissue patterns being formed by cell sorting.
Submitted by Christina Schilde [[log in to unmask]]
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[End dictyNews, volume 40, number 20]
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