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Electronic Edition
Volume 46, number 7
March 6, 2020
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Abstracts
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The multifarious lysozyme arsenal of Dictyostelium discoideum
Otmane Lamrabet1*, Tania Jauslin1, Wanessa Cristina Lima1,
Matthias Leippe2, Pierre Cosson1
1 Faculty of Medicine, University of Geneva, Centre Médical Universitaire,
1 rue Michel Servet, CH-1211, Geneva 4, Switzerland
2 Zoological Institute, Comparative Immunobiology, University of Kiel,
Kiel, Germany
*Correspondence: [log in to unmask]
Developmental & Comparative Immunology, 107 (2020) 103645.
doi.org/10.1016/j.dci.2020.103645
Dictyostelium discoideum is a free-living soil amoeba which feeds upon
bacteria. To bind, ingest, and kill bacteria, D. discoideum uses molecular
mechanisms analogous to those found in professional phagocytic cells of
multicellular organisms. D. discoideum is equipped with a large arsenal of
antimicrobial peptides and proteins including amoebapore-like peptides and
lysozymes. This review describes the family of lysozymes in D. discoideum.
We identified 22 genes potentially encoding four different types of lysozymes
in the D. discoideum genome. Although most of these genes are also
present in the genomes of other amoebal species, no other organism is as
well-equipped with lysozyme genes as D. discoideum.
submitted by: Otmane Lamrabet [[log in to unmask]]
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Single-molecule imaging of PI(4,5)P2 and PTEN in vitro reveals a positive
feedback mechanism for PTEN membrane binding
Daisuke Yoshioka, Seiya Fukushima, Hiroyasu Koteishi, Daichi Okuno,
Toru Ide, Satomi Matsuoka and Masahiro Ueda
Communications Biology, 3, Article number: 92.
https://doi.org/10.1038/s42003-020-0818-3
PTEN, a 3-phosphatase of phosphoinositide, regulates asymmetric
PI(3,4,5)P3 signaling for the anterior-posterior polarization and migration
of motile cells. PTEN acts through posterior localization on the plasma
membrane, but the mechanism for this accumulation is poorly understood.
Here we developed an in vitro single-molecule imaging assay with various
lipid compositions and use it to demonstrate that the enzymatic product,
PI(4,5)P2, stabilizes PTEN’s membrane-binding. The dissociation kinetics
and lateral mobility of PTEN depended on the PI(4,5)P2 density on artificial
lipid bilayers. The basic residues of PTEN were responsible for electrostatic
interactions with anionic PI(4,5)P2 and thus the PI(4,5)P2-dependent
stabilization. Single-molecule imaging in living Dictyostelium cells revealed
that these interactions were indispensable for the stabilization in vivo, which
enabled efficient cell migration by accumulating PTEN posteriorly to restrict
PI(3,4,5)P3 distribution to the anterior. These results suggest that
PI(4,5)P2-mediated positive feedback and PTEN-induced PI(4,5)P2
clustering may be important for anterior-posterior polarization.
submitted by: Satomi Matsuoka [[log in to unmask]]
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IDIRS retrotransposons amplify via linear, single-stranded cDNA
intermediates
Marek Malicki, Thomas Spaller, Thomas Winckler and Christian Hammann
Nucleic Acids Research, in press
The Dictyostelium Intermediate Repeat Sequence 1 (DIRS-1) is the name-
giving member of the DIRS order of tyrosine recombinase retrotransposons.
In Dictyostelium discoideum, DIRS-1 is highly amplified and enriched in
heterochromatic centromers of the D. discoideum genome. We show here
that DIRS-1 it tightly controlled by the D. discoideum RNA interference
machinery and is only mobilized in mutants lacking either the RNA
dependent RNA polymerase RrpC or the Argonaute protein AgnA. DIRS
retrotransposons contain an internal complementary region (ICR) that is
thought to be required to reconstitute a full-length element from incomplete
RNA transcripts. Using different versions of D. discoideum DIRS-1 equipped
with retrotransposition marker genes, we show experimentally that the ICR
is in fact essential to complete retrotransposition. We further show that
DIRS-1 produces a mixture of single-stranded, mostly linear
extrachromosomal cDNA intermediates. If this cDNA is isolated and
transformed into D. discoideum cells, it can be used by DIRS-1 proteins to
complete productive retrotransposition. This work provides the first
experimental evidence to propose a general retrotransposition mechanism
of the class of DIRS like tyrosine recombinase retrotransposons.
submitted by: Christian Hammann [[log in to unmask]]
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