dictyNews
Electronic Edition
Volume 41, number 18
August 28, 2015
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Abstracts
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A host factor supports retrotransposition of the TRE5-A population
in Dictyostelium cells by suppressing an Argonaute protein
Anika Schmith1, Thomas Spaller1, Friedemann Gaube1, Åsa Fransson2,
Benjamin Boesler3, Sandeep Ojha4, Wolfgang Nellen3,
Christian Hammann4, Fredrik Söderbom5, Thomas Winckler1
1 Department of Pharmaceutical Biology, Institute of Pharmacy,
University of Jena, Germany
2 Department of Molecular Biology, Biomedical Center, Swedish
University of Agricultural Sciences, Uppsala, Sweden
3 Institute of Biology – Genetics, University of Kassel, Germany
4 Ribogenetics@Biochemistry Lab, Department of Life Sciences
and Chemistry, Molecular Life Sciences Research Center, Jacobs
University Bremen, Germany
5 Department of Cell and Molecular Biology, Biomedical Center,
Uppsala University, Sweden
Mobile DNA, in press
Background: In the compact and haploid genome of Dictyostelium
discoideum control of transposon activity is of particular
importance to maintain viability. The non-long terminal repeat
retrotransposon TRE5-A amplifies continuously in D. discoideum
cells even though it produces considerable amounts of minus-strand
(antisense) RNA in the presence of an active RNA interference
machinery. Removal of the host-encoded C-module-binding factor
(CbfA) from D. discoideum cells resulted in a more than 90%
reduction of both plus- and minus-strand RNA of TRE5-A and a
strong decrease of the retrotransposition activity of the cellular
TRE5-A population. Transcriptome analysis revealed an
approximately 230-fold overexpression of the gene coding for the
Argonaute-like protein AgnC in a CbfA-depleted mutant.
Results: The D. discoideum genome contains orthologs of RNA-
dependent RNA polymerases, Dicer-like proteins, and Argonaute
proteins that are supposed to represent RNA interference pathways.
We analyzed available mutants in these genes for altered
expression of TRE5-A. We found that the retrotransposon was
overexpressed in mutants lacking the Argonaute proteins AgnC and
AgnE. Because the agnC gene is barely expressed in wild-type cells,
probably due to repression by CbfA, we employed a new method of
promoter-swapping to overexpress agnC in a CbfA-independent manner.
In these strains we established an in vivo retrotransposition assay
that determines the retrotransposition frequency of the cellular
TRE5-A population. We observed that both the TRE5-A steady-state RNA
level and retrotransposition rate dropped to less than 10% of
wild-type in the agnC overexpressor strains.
Conclusions: The data suggest that TRE5-A amplification is controlled
by a distinct pathway of the Dictyostelium RNA interference machinery
that does not require RNA-dependent RNA polymerases but involves AgnC.
This control is at least partially overcome by the activity of CbfA,
a factor derived from the retrotransposon's host. This unusual
regulation of mobile element activity most likely had a profound
effect on genome evolution in D. discoideum.
Submitted by Thomas Winckler [[log in to unmask]]
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Organization of microtubule assemblies in Dictyostelium syncytia
depends on the microtubule crosslinker, Ase1
Irina Tikhonenko, Karen Irizarry, Alexey Khodjakov, and
Michael P. Koonce
Division of Translational Medicine
Wadsworth Center
NYS Department of Health
Albany, NY 12201-0509
Cell Molecular Life Sciences, in press
It has long been known that the interphase microtubule (MT) array
is a key cellular scaffold that provides structural support and
directs organelle trafficking in eukaryotic cells. Although in
animal cells, a combination of centrosome nucleating properties
and polymer dynamics at the distal microtubule ends is generally
sufficient to establish a radial, polar array of MTs, little is
known about how effector proteins (motors and crosslinkers) are
coordinated to produce the diversity of interphase MT array
morphologies found in nature. This diversity is particularly
important in multinucleated environments where multiple MT arrays
must coexist and function. We initiate here a study to address
the higher ordered coordination of multiple, independent MT
arrays in a common cytoplasm. Deletion of a MT crosslinker of the
MAP65/Ase1/PRC1 family disrupts the spatial integrity of multiple
arrays in Dictyostelium discoideum, reducing the distance between
centrosomes and increasing the intermingling of MTs with opposite
polarity. This result, coupled with previous dynein disruptions
suggest a robust mechanism by which interphase MT arrays can
utilize motors and crosslinkers to sense their position and
minimize overlap in a common cytoplasm.
Submitted by Mike Koonce [[log in to unmask]]
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[End dictyNews, volume 41, number 18]
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