dictyNews
Electronic Edition
Volume 45, number 13
MAY 3, 2019
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Abstracts
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Cyclic AMP induction of Dictyostelium prespore gene expression
requires autophagy
Yoko Yamada and Pauline Schaap*
School of Life Sciences, University of Dundee, DD15EH,
Dundee, UK
Developmental Biology, in press
Dictyostelium discoideum amoebas display colonial multicellularity
where starving amoebas aggregate to form migrating slugs and
fruiting bodies consisting of spores and three supporting cell types.
To resolve the cell signalling mechanism that control sporulation,
we use insertional mutagenesis of amoebas transformed with fusion
constructs of spore genes and red fluorescent protein. We identified
the defective gene in a mutant lacking spore gene expression as the
autophagy gene Atg7. Directed knock-out of atg7 and of autophagy
genes like atg5 and atg9 yielded a similar phenotype, with lack of
viable spores and excessive differentiation of stalk cells. The atg7-,
atg5- and atg9- cells were specifically defective in cAMP induction of
prespore genes, but showed enhanced cAMP stimulation of prestalk
genes at the same developmental stage. The lack of prespore gene
induction in the autophagy mutants was not due to deleterious effects
of loss of autophagy on known components of the cAMP pathway,
such as cAMP receptors and their cAMP-induced phosphorylation
and internalization, PKA and the transcription factors SpaA and GbfA,
or to lack of NH3 production by proteolysis, which was previously
suggested to stimulate the spore pathway. Our continued mutagenesis
approach is the most likely to yield the intriguing link between
autophagy and prespore gene induction.
submitted by: Pauline Schaap [[log in to unmask]]
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A Terpene Synthase-Cytochrome P450 Cluster in Dictyostelium
discoideum Produces a Novel Trisnorsesquiterpene.
Chen, X., Luck, K., Rabe, P., Dinh, C.Q.D., Shaulsky, G., Nelson,
D.R., Gershenzon, J., Dickschat, J.S., Köllner, T.G., and Chen, F.
eLife, in press
Author-approved pdf: https://elifesciences.org/articles/44352
Terpenoids are enormously diverse, but our knowledge of their
biosynthesis and functions is limited. Here we report on a terpene
synthase (DdTPS8)-cytochrome P450 (CYP521A1) gene cluster
that produces a novel C12 trisnorsesquiterpene and affects the
development of Dictyostelium discoideum. DdTPS8 catalyzes the
formation of a sesquiterpene discoidol, which is undetectable from
the volatile bouquet of wild type D. discoideum. Interestingly, a
DdTPS8 knockout mutant lacks not only discoidol, but also a
putative trisnorsesquiterpene. This compound was hypothesized
to be derived from discoidol via cytochrome P450 (CYP)-catalyzed
oxidative cleavage. CYP521A1, which is clustered with DdTPS8,
was identified as a top candidate. Biochemical assays
demonstrated that CYP521A1 catalyzes the conversion of
discoidol to a novel trisnorsesquiterpene named discodiene. The
DdTPS8 knockout mutant exhibited slow progression in development.
This study points to the untapped diversity of natural products made
by D. discoideum, which may have diverse roles in its development
and chemical ecology.
submitted by: Gad Shaulsky [[log in to unmask]]
——————————————————————————————————————
Force Balances Between Interphase Centrosomes, as Revealed
by Laser Ablation
Jacob Odell, Vitali Sikirzhytski, Irina Tikhonenko, Sonila Cobani,
Alexey Khodjakov, and Michael Koonce
Mol. Biol. Cell, in press
Numerous studies have highlighted the self-centering activities of
individual microtubule arrays in animal cells, but relatively few works
address the behavior of multiple arrays that coexist in a common
cytoplasm. In multinucleated Dictyostelium discoideum cells, each
centrosome organizes a radial microtubule network and these
networks remain separate from one another. This feature offers an
opportunity to reveal mechanism(s) responsible for positioning of
multiple centrosomes. Using a laser microbeam to eliminate one of
the two centrosomes in binucleate cells, we show that the unaltered
array is rapidly repositioned at the cell center. This result
demonstrates that each microtubule array is constantly subject to
centering forces and infers a mechanism to balance the positions of
multiple arrays. Our results address the limited actions of three
kinesins and a crosslinking MAP that are known to have effects in
maintaining microtubule organization, and suggest a simple means
used to keep the arrays separated.
submitted by: Michael Koonce [[log in to unmask]]
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[End dictyNews, volume 45, number 13]
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