dictyNews
Electronic Edition
Volume 42, number 14
May 20, 2016
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Abstracts
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Dictyostelium EHD associates with Dynamin and participates in
phagosome maturation
Aurιlie Gueho1, Cristina Bosmani1, Navin Gopaldass2, Virginie Molle3,
Thierry Soldati1, and Franηois Letourneur3*
1Department of Biochemistry, University of Geneva, CH-1211 Geneva,
Switzerland
2Department of Biochemistry, University of Lausanne, CH-1066
Epalinges, Switzerland
3Laboratoire de Dynamique des Interactions Membranaires Normales
et Pathologiques, Universitι de Montpellier, CNRS, UMR 5235,
Place Eugθne Bataillon, 34095 Montpellier Cedex 05, France.
*Author for correspondence ([log in to unmask])
Journal of Cell Science, in press
C-terminal EHDs (Eps15 homology-domain-containing proteins) are
newly identified key regulators of endosomal membrane trafficking.
Here we show that D. discoideum contains a single EHD protein that
localizes to endosomal compartments and newly formed phagosomes.
We provide the first evidence that EHD regulates phagosome
maturation. Deletion of EHD results in defects in intraphagosomal
proteolysis and acidification. These defects are linked to early
delivery of lysosomal enzymes and fast retrieval of the vacuolar
H+-ATPase in maturing phagosomes. We also demonstrate that EHD
physically interacts with DymA. Our results indicate that EHD
and DymA can associate independently to endomembranes, and yet
they share identical kinetics of phagosome recruitment and
release during phagosome maturation. Functional analysis of
ehd-, dymA-, and double dymA-/ehd- knock-out strains indicate that
DymA and EHD play non-redundant independent functions in
phagosome maturation. Finally, we show that the absence of EHD
leads to increase tubulation of endosomes, indicating that EHD
participates in the scission of endosomal tubules as reported
for DymA.
submitted by: Franηois Letourneur [[log in to unmask]]
Two HAP2-GCS1 homologs responsible for gamete interactions in
the cellular slime mold with multiple mating types: Implication
for common mechanisms of sexual reproduction shared by plants and
protozoa and for male-female differentiation
Marina Okamoto, Lixy Yamada, Yukie Fujisaki, Gareth Bloomfield,
Kentaro Yoshida, Hidekazu Kuwayama, Hitoshi Sawada, Toshiyuki
Mori, and Hideko Urushihara
Developmental Biology, in press
Fertilization is a central event in sexual reproduction, and
understanding its molecular mechanisms has both basic and
applicative biological importance. Recent studies have
uncovered the molecules that mediate this process in a variety
of organisms, making it intriguing to consider conservation and
evolution of the mechanisms of sexual reproduction across phyla.
The social amoeba Dictyostelium discoideum undergoes sexual
maturation and forms gametes under dark and humid conditions.
It exhibits three mating types, type-I, -II, and -III, for the
heterothallic mating system. Based on proteome analyses of the
gamete membranes, we detected expression of two homologs of
the plant fertilization protein HAP2-GCS1. When their coding
genes were disrupted in type-I and type-II strains, sexual
potency was completely lost, whereas disruption in the type-III
strain did not affect mating behavior, suggesting that the
latter acts as female in complex organisms. Our results
demonstrate the highly conserved function of HAP2-GCS1 in
gamete interactions and suggest the presence of additional
allo-recognition mechanisms in D. discoideum gametes.
submitted by: Hideko Urushihara [[log in to unmask]]
Analysis of the microprocessor in Dictyostelium:
the role of RbdB, a dsRNA binding protein.
Doreen Meier, Janis Kruse, Jann Buttlar, Michael Friedrich,
Fides Zenk, Benjamin Boesler, Konrad U. Fφrstner,
Christian Hammann, Wolfgang Nellen.
PLoS Genetics, accepted
We identified the dsRNA binding protein RbdB as an essential component
in miRNA processing in Dictyostelium discoideum. RbdB is a nuclear
protein that accumulates, together with Dicer B, in nucleolar foci reminiscent
of plant dicing bodies. Disruption of rbdB results in loss of miRNAs and
accumulation of primary miRNAs. The phenotype can be rescued by ectopic
expression of RbdB thus allowing for a detailed analysis of domain function.
The lack of cytoplasmic dsRBD proteins involved in miRNA processing,
suggests that both processing steps take place in the nucleus thus
resembling the plant pathway. However, we also find features e.g. in the
domain structure of Dicer which suggest similarities to animals. Reduction
of miRNAs in the rbdB- strain and their increase in the Argonaute A knock
out allowed the definition of new miRNAs one of which appears to belong
to a new non-canonical class.
submitted by: Wolfgang Nellen [[log in to unmask]]
Mechanism and biological role of Dnmt2 in Nucleic Acid
Methylation
Albert Jeltsch, Ann Ehrenhofer-Murray, Tomasz Jurkowski,
Frank Lyko, Gunter Reuter, Serge Ankri, Wolfgang Nellen,
Matthias Schaefer & Mark Helm
RNA Biology, in press
A group of homologous nucleic acid modification enzymes called Dnmt2,
Trdmt1, Pmt1, DnmA, and Ehmet in different model organisms catalyse
the transfer of a methyl group from the cofactor S-adenosyl-methionine
(SAM) to the carbon-5 of cytosine residues. Originally considered as
DNA MTases, these enzymes were shown to be tRNA methyltransferases
about a decade ago. Between the presumed involvement in DNA
modification-related epigenetics, and the recent foray into the RNA
modification field, significant progress has characterized Dnmt2-related
research. Here, we review this progress in its diverse facets including
molecular evolution, structural biology, biochemistry, chemical biology,
cell biology and epigenetics.
submitted by: Wolfgang Nellen [[log in to unmask]]
Gene discovery by chemical mutagenesis and whole-genome
sequencing in Dictyostelium
Cheng-Lin Frank Li, Balaji Santhanam, Amanda Nicole Webb,
Bla Zupan,1 and Gad Shaulsky
Baylor College of Medicine and University of Ljubljana
Genome Research, in press
Whole-genome sequencing is a useful approach for identification of
chemical-induced lesions, but previous applications involved tedious
genetic mapping to pinpoint the causative mutations. We propose that
saturation mutagenesis under low mutagenic loads, followed by
whole-genome sequencing, should allow direct implication of genes
by identifying multiple independent alleles of each relevant gene. We
tested the hypothesis by performing three genetic screens with
chemical mutagenesis in the social soil amoeba Dictyostelium
discoideum. Through genome sequencing, we successfully identified
mutant genes with multiple alleles in near-saturation screens,
including resistance to intense illumination and strong suppressors of
defects in an allorecognition pathway. We tested the causality of the
mutations by comparison to published data and by direct
complementation tests, finding both dominant and recessive causative
mutations. Therefore, our strategy provides a cost- and time-efficient
approach to gene discovery by integrating chemical mutagenesis and
whole-genome sequencing. The method should be applicable to many
microbial systems, and it is expected to revolutionize the field of
functional genomics in Dictyostelium by greatly expanding the mutation
spectrum relative to other common mutagenesis methods.
submitted by: Gad Shaulsky [[log in to unmask]]
Uses and abuses of macropinocytosis
Gareth Bloomfield and Robert R. Kay
MRC Laboratory of Molecular Biology, Francis Crick Avenue,
Cambridge Biomedical Campus, Cambridge, CB2 0QH, UK
J. Cell Science, in press
Macropinocytosis is a means by which eukaryotic cells ingest
extracellular liquid and dissolved molecules. It is widely
conserved amongst cells that can take on amoeboid form, and
therefore appears to be an ancient feature that can be traced back
to an early stage of evolution. Recent advances have highlighted
how this endocytic process can be subverted during pathology:
certain cancer cells use macropinocytosis to feed on extracellular
protein, and many viruses and bacteria use it to enter host cells.
Prion and prion-like proteins can also spread and propagate from
cell to cell via macropinocytosis. Progress is being made towards
using macropinocytosis therapeutically, either to deliver drugs to or
cause cell death by inducing catastrophically rapid fluid uptake.
Mechanistically, the Ras signalling pathway plays a prominent and
conserved activating role in amoebae and in mammals; mutant
amoebae with abnormally high Ras activity resemble tumour cells
in their increased capacity for growth using nutrients ingested by
macropinocytosis. This Commentary takes a functional and
evolutionary perspective to highlight progress in understanding and
utilising macropinocytosis, which is viewed as an ancient feeding
process used by single-celled phagotrophs but now put to varied
uses by metazoan cells and abused in disease states, including
submitted by: Gad Shaulsky [[log in to unmask]]
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[End dictyNews, volume 42, number 14]
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