dictyNews
Electronic Edition
Volume 47, number 15
July 9, 2021
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Abstracts
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Regulation of the Actin Cytoskeleton via Rho GTPase Signalling in
Dictyostelium and Mammalian Cells: A Parallel Slalom
Vedrana Filic *, Lucija Mijanovic, Darija Putar, Antea Talajic, Helena
Cetkovic and Igor Weber *
Division of Molecular Biology, Ruder Boskovic Institute, Bijenicka 54,
HR-10000 Zagreb, Croatia
*correspondence: [log in to unmask], [log in to unmask]
Cells, published; https://www.mdpi.com/2073-4409/10/7/1592
Both Dictyostelium amoebae and mammalian cells are endowed
with an elaborate actin cytoskeleton that enables them to perform a
multitude of tasks essential for survival. Although these organisms
diverged more than a billion years ago, their cells share the capability
of chemotactic migration, large-scale endocytosis, binary division
effected by actomyosin contraction, and various types of adhesions to
other cells and to the extracellular environment. The composition and
dynamics of the transient actin-based structures that are engaged in
these processes are also astonishingly similar in these evolutionary
distant organisms. The question arises whether this remarkable
resemblance in the cellular motility hardware is accompanied by a
similar correspondence in matching software, the signalling networks
that govern the assembly of the actin cytoskeleton. Small GTPases
from the Rho family play pivotal roles in the control of the actin
cytoskeleton dynamics. Indicatively, Dictyostelium matches mammals
in the number of these proteins. We give an overview of the Rho
signalling pathways that regulate the actin dynamics in Dictyostelium
and compare them with similar signalling networks in mammals. We
also provide a phylogeny of Rho GTPases in Amoebozoa, which
shows a variability of the Rho inventories across different clades
found also in Metazoa.
submitted by: Darija Putar [[log in to unmask]]
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A ‘dynamic adder model’ for cell size homeostasis in Dictyostelium cells
Masahito Tanaka, Toshiko Kitanishi-Yumura, Shigehiko Yumura
Scientific Reports; https://rdcu.be/cnCw5
After a cell divides into two daughter cells, the total cell surface area of
the daughter cells should increase to the original size to maintain cell
size homeostasis in a single cell cycle. Previously, three models have
been proposed to explain the regulation of cell size homeostasis: sizer,
timer, and adder models. Here, we precisely measured the total cell
surface area of Dictyostelium cells in a whole cell cycle by using the
agar-overlay method, which eliminated the influence of surface membrane
reservoirs, such as microvilli and membrane wrinkles. The total cell surface
area exponentially increased during interphase, slightly decreased at
metaphase, and then increased by approximately 20% during cytokinesis.
From the analysis of the added surface area, we concluded that the cell
size was regulated by the adder or near-adder model in interphase. This
adder model is not caused by a simple cell membrane addition, but is
more dynamic due to the rapid cell membrane turnover. We propose a
‘dynamic adder model’ to explain cell size homeostasis in interphase.
submitted by: Shigehiko Yumura [[log in to unmask]]
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Annotating Putative D. discoideum Proteins Using I-TASSER
Jacquelyn McCullough1, Petra Fey2, Ryan Rahman1, Morgan Wallace1,
Seeta Morey1, Kyle Sahlberg1, Ethan McGonagle1, Danielle Hess1,
Chance Hatfield, 1 Michaela-Romina Sarmiento1, Jordi Velasquez1,
and Richard H. Gomer1
1Department of Biology, Texas A&M University,
2Center for Genetic Medicine, Northwestern University
microPublication Biology, in press
Using Gene Ontology annotation in any aspect or using any evidence
code, we found that approximately 14% percent of predicted D. discoideum
proteins have no GO annotations and no obvious similarity to any annotated
protein across diverse organisms. We have been systematically examining
these unannotated protein sequences using software that predicts a protein
structure and then compares the predicted structure to known structures.
submitted by: Richard Gomer [[log in to unmask]]
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Loss Of Pikfyve Causes Transdifferentiation Of Dictyostelium Spores Into
Basal Disc Cells
Yoko Yamada1,2,3, Gillian Forbes1, Qingyou Du1, Takefumi Kawata2*
and Pauline Schaap1*
1School of Life Sciences, University of Dundee, Dundee DD15EH, UK
2Department of Biology, Faculty of Science, Toho University, Funabashi,
Chiba 274-8510, Japan
3Department of Materials and Life Sciences, Faculty of Science and
Technology, Sophia University, Tokyo 102-8554, Japan
Frontiers in Cell and Developmental Biology, in press
The 1-phosphatidylinositol-3-phosphate 5-kinase PIKfyve generates
PtdIns3,5P2 on late phagolysosomes, which by recruiting the scission
protein Atg18, results in their fragmentation in the normal course of
endosome processing. Loss of PIKfyve function results in cellular
hypervacuolization in eukaryotes and organ failure in humans. We
identified pikfyve as the defective gene in a Dictyostelium mutant that
failed to form spores. The amoebas normally differentiated into prespore
cells and initiated spore coat protein synthesis in Golgi-derived prespore
vesicles. However, instead of exocytosing, the prespore vesicles fused
into the single vacuole that typifies the stalk and basal disc cells that
support the spores. This process was accompanied by stalk wall
biosynthesis, loss of spore gene expression and overexpression of
ecmB, a basal disc and stalk-specific gene, but not of the stalk-specific
genes DDB_G0278745 and DDB_G0277757. Transdifferentiation of
prespore into stalk-like cells was previously observed in mutants that lack
early autophagy genes, like atg5, atg7 and atg9. However, while
autophagy mutants specifically lacked cAMP induction of prespore gene
expression, Pikfyve- showed normal early autophagy and prespore
induction, but increased in vitro induction of ecmB. Combined, the data
suggest that the Dictyostelium endosomal system influences cell fate by
acting on cell type specific gene expression.
submitted by: Pauline Schaap [[log in to unmask]]
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A Dictyostelium model for BPAN disease reveals a functional relationship
between the WDR45/WIPI4 homolog Wdr45l and Vmp1 in the regulation
of autophagy-associated PtdIns3P and ER stress
Alba Tornero-Écija, Luis-Carlos Tábara, Miranda Bueno-Arribas, Laura
Antón-Esteban, Cristina Navarro-Gómez, Irene Sánchez, Olivier Vincent
and Ricardo Escalante
Autophagy, in press
PROPPINs are conserved PtdIns3P-binding proteins required for
autophagosome biogenesis that fold into a characteristic group of
seven-bladed beta-propellers. Mutations in WDR45/WIPI4, a human
member of this family, lead to BPAN, a rare form of neurodegeneration.
We have generated mutants for the two PROPPIN proteins present in
the model system Dictyostelium discoideum (Atg18 and Wdr45l) and
characterized their function. Lack of Wdr45l greatly impairs autophagy,
while Atg18 only causes subtle defects in the maturation of
autolysosomes. The strong phenotype of the Wdr45l mutant is strikingly
similar to that observed in Dictyostelium cells lacking Vmp1, an ER
protein required for omegasome formation. Common phenotypes include
impaired growth in axenic medium, lack of aggregation, and local
enrichment of PtdIns3P as determined by the use of lipid reporters. In
addition, Vmp1 and Wdr45l mutants show a chronically active response
to ER stress. For both mutants, this altered PtdIns3P localization can be
prevented by the additional mutation of the upstream regulator Atg1,
which also leads to recovery of axenic growth and reduction of ER stress.
We propose that, in addition to an autophagy defect, local autophagy-
associated PtdIns3P accumulation might contribute to the pathogenesis
of BPAN by disrupting ER homeostasis. The introduction of BPAN-
associated mutations in Dictyostelium Wdr45l reveals the impact of
pathogenic residues on the function and localization of the protein.
submitted by: Ricardo Escalante [[log in to unmask]]
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[End dictyNews, volume 47, number 15]
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