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dictyNews Volume 41 Number 26
dictyNews
Electronic Edition
Volume 41, number 26
December 12, 2015
Please submit abstracts of your papers as soon as they have been
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Abstracts
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The two Dictyostelium autophagy eight proteins, ATG8a and ATG8b,
associate with the autophagosome in succession
Jan Matthias, Susanne Meßling and Ludwig Eichinger
European Journal of Cell Biology, in press.
Autophagy is an ancient cellular pathway that is conserved from
yeast to man. It contributes to many physiological and pathological
processes and plays a major role in the degradation of proteins
and/or organelles in response to starvation and stress. In the
autophagic process cytosolic material is captured into double
membrane-bound vesicles, the autophagosomes. After fusion with
lysosomes, the cargo is degraded in the generated autolysosomes and
then recycled for further use.Autophagy 8 (ATG8, in mammals LC3), a
well-established marker of autophagy, is covalently linked to
phosphatidylethanolamine on the autophagic membrane during
autophagosome formation. Bioinformatic analysis of the Dictyostelium
genome revealed two atg8 genes which encode the ATG8a and ATG8b
paralogs, which are with around 14 kDa similar in size, 54 % identical
to one another and more closely related to the corresponding proteins
in fungi and plants than in animals. For ATG8a we found a strong up-
regulation throughout the 24 h developmental time course while ATG8b
expression was highest in vegetative cells followed by a moderate
reduction during early development. Confocal microscopy of
fluorescently tagged ATG8a and ATG8b in vegetative AX2 wild-type and
in ATG9 minus cells showed that both proteins mainly co-localised on
vesicular structures with a diameter above 500 nm while those smaller
than 500 nm were predominantly positive for ATG8b. In ATG9 minus cells
we found a strong increase in the relative abundance of ATG8a-positive
large vesicular structures and of total ATG8b-positive structures per
cell indicating autophagic flux problems in this mutant. We also found
that vesicular structures positive for ATG8a and/or ATG8b were also
positive for ubiquitin. Live cell imaging of AX2 and ATG9 minus cells
co-expressing combinations of red and green tagged ATG8a, ATG8b or
ATG9 revealed transient co-localisations of these proteins. Our results
suggest that ATG8b associates with nascent autophagosomes before
ATG8a. We further find that the process of autophagosome formation in
Dictyostelium is highly dynamic. We infer from our data that
Dictyostelium ATG8a and ATG8b have distinct functions in autophagosome
formation and that ATG8b is the functional ortholog of the mammalian
LC3 subfamily and ATG8a of the GABARAP subfamily.
submitted by: Ludwig Eichinger [ludwig.eichinger@uni-koeln.de]
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[End dictyNews, volume 41, number 26]
