dictyNews
Electronic Edition
Volume 45, number 5
February 15, 2019
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Abstracts
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Recent Insights into NCL Protein Function Using the Model Organism
Dictyostelium discoideum
Meagan D. McLaren, Sabateeshan Mathavarajah, Robert J. Huber
Department of Biology, Trent University, Peterborough, ON, Canada
Cells, 2019
Special Issue: Simple Organisms for Complex Problems: Modeling
Human Disease in Yeast and Dictyostelium
The neuronal ceroid lipofuscinoses (NCLs) are a group of devastating
neurological disorders that have a global distribution and affect people
of all ages. Commonly known as Batten disease, this form of
neurodegeneration is linked to mutations in 13 genetically distinct genes.
The precise mechanisms underlying the disease are unknown, in large
part due to our poor understanding of the functions of NCL proteins.
The social amoeba Dictyostelium discoideum has proven to be an
exceptional model organism for studying a wide range of neurological
disorders, including the NCLs. The Dictyostelium genome contains
homologs of 11 of the 13 NCL genes. Its life cycle, comprised of both
single-cell and multicellular phases, provides an excellent system for
studying the effects of NCL gene deficiency on conserved cellular and
developmental processes. In this review, we highlight recent advances
in NCL research using Dictyostelium as a biomedical model.
submitted by: Robert Huber [[log in to unmask]]
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Comparative transcriptomics reveals mechanisms underlying
cln3-deficiency phenotypes in Dictyostelium
Robert J. Huber, Sabateeshan Mathavarajah
Department of Biology, Trent University, Peterborough, ON, Canada
Cellular Signalling, in press
Mutations in CLN3 cause a juvenile form of neuronal ceroid
lipofuscinosis (NCL). This devastating neurological disorder, commonly
known as Batten disease, is currently untreatable due to a lack of
understanding of the physiological role of the protein. Recently, work in
the social amoeba Dictyostelium discoideum has provided valuable
new insight into the function of CLN3 in the cell. Research has linked
the Dictyostelium homolog (gene: cln3, protein: Cln3) to protein
secretion, adhesion, and aggregation during starvation, which initiates
multicellular development. In this study, we used comparative
transcriptomics to explore the mechanisms underlying the aberrant
response of cln3- cells to starvation. During starvation, 1153 genes
were differentially expressed in cln3- cells compared to WT. Among
the differentially expressed genes were homologs of other human NCL
genes including TPP1/CLN2, CLN5, CTSD/CLN10, PGRN/CLN11, and
CTSF/CLN13. STRING and GO term analyses revealed an enrichment
of genes linked to metabolic, biosynthetic, and catalytic processes. We
then coupled the findings from the RNA-seq analysis to biochemical
assays, specifically showing that loss of cln3 affects the expression and
activity of lysosomal enzymes, increases endo-lysosomal pH, and alters
nitric oxide homeostasis. Finally, we show that cln3- cells accumulate
autofluorescent storage bodies during starvation and provide evidence
linking the function of Cln3 to Tpp1 and CtsD activity. In total, this study
enhances our knowledge of the molecular mechanisms underlying Cln3
function in Dictyostelium.
submitted by: Robert Huber [[log in to unmask]]
——————————————————————————————————————
Functional integrity of the contractile actin cortex is safeguarded by
multiple Diaphanous-related formins
Christof Litschko1,*, Stefan Brühmann1,*, Agnes Csiszár2, Till Stephan1,
Vanessa Dimchev3,4, Julia Damiano-Guercio1, Alexander Junemann1,
Sarah Körber1, Moritz Winterhoff1, Benjamin Nordholz1,†, Nagendran
Ramalingam5, Michelle Peckham6, Klemens Rottner3,4, Rudolf Merkel2
and Jan Faix1,#
1 Institute for Biophysical Chemistry, Hannover Medical School,
Carl-Neuberg-Str. 1, 30625 Hannover, Germany;
2 Institute of Complex Systems, ICS-7: Biomechanics, Forschungszentrum
Jülich GmbH, 52425 Jülich, Germany.
3 Division of Molecular Cell Biology, Zoological Institute, Technische
Universität Braunschweig, Spielmannstrasse 7, 38106 Braunschweig,
Germany.
4 Molecular Cell Biology Group, Helmholtz Centre for Infection Research,
Inhoffenstrasse 7, 38124 Braunschweig, Germany.
5 Ann Romney Center for Neurologic Diseases, Brigham and Women’s
Hospital, Harvard Medical School, 60 Fenwood Road, Boston, MA 02115,
United States of America;
6 Astbury Centre for Structural Molecular Biology, University of Leeds,
Leeds, UK.
* These authors contributed equally to this study. #Correspondence
should be addressed to J.F. ([log in to unmask])
PNAS, in press
The contractile actin cortex is a thin layer of filamentous actin, myosin
motors and regulatory proteins beneath the plasma membrane crucial
to cytokinesis, morphogenesis and cell migration. However, the factors
regulating actin assembly in this compartment are not well understood.
Using the Dictyostelium model system, we show that the three
Diaphanous-related formins (DRFs) ForA, ForE and ForH are regulated
by the RhoA-like GTPase RacE and synergize in the assembly of
filaments in the actin cortex. Single or double formin-null mutants
displayed only moderate defects in cortex function whereas the
concurrent elimination of all three formins or of RacE caused massive
defects in cortical rigidity and architecture as assessed by aspiration
assays and electron microscopy. Consistently, the triple formin- and
RacE-mutants encompassed large peripheral patches devoid of cortical
F-actin and exhibited severe defects in cytokinesis and multicellular
development. Unexpectedly, many forA-/H-/E- and racE--mutants
protruded efficiently, formed multiple exaggerated fronts and migrated
with morphologies reminiscent of rapidly-moving fish keratocytes. In
2D-confinement, however, these mutants failed to properly polarize and
recruit myosin II to the cell rear essential for migration. Cells arrested
in these conditions displayed dramatically amplified flow of cortical actin
filaments, as revealed by TIRF-imaging and iterative particle image
velocimetry (PIV). Consistently, individual and combined, CRISPR/
Cas9-mediated disruption of genes encoding mDia1 and -3 formins in
B16-F1 mouse melanoma cells revealed enhanced frequency of cells
displaying multiple fronts, again accompanied by defects in cell
polarization and migration. These results suggest evolutionarily
conserved functions for formin-mediated actin assembly in actin
cortex mechanics.
submitted by: Jan Faix [[log in to unmask]]
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[End dictyNews, volume 45, number 5]
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