dictyNews
Electronic Edition
Volume 38, number 23
September 14, 2012
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Abstracts
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Amino acid repeats cause extraordinary coding sequence
variation in the social amoeba Dictyostelium discoideum
Clea Scala1 *, Xiangjun Tian2 *, Natasha J. Mehdiabadi1,3,,
Margaret H. Smith1, Gerda Saxer4, Katie Stephens1,
Prince Buzombo1, Joan E. Strassmann2, David C. Queller2
PLoS One, in press
Protein sequences are normally the most conserved elements
of genomes owing to purifying selection to maintain their
functions. We document an extraordinary amount of
within-species protein sequence variation in the model
eukaryote Dictyostelium discoideum stemming from triplet
DNA repeats coding for long strings of single amino acids.
D. discoideum has a very large number of such strings, many
of which are polyglutamine repeats, the same sequence that
causes various human neurological disorders in humans, like
Huntington’s disease. We show here that D. discoideum
coding repeat loci are highly variable among individuals, making
D. discoideum a candidate for the most variable proteome.
The coding repeat loci are not significantly less variable than
similar non-coding triplet repeats. This pattern is consistent
with these amino-acid repeats being largely non-functional
sequences evolving primarily by mutation and drift.
Submitted by David Queller [[log in to unmask]]
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Mitochondrial fission and fusion in Dictyostelium discoideum:
a search for proteins involved in membrane dynamics
Brixey G Schimmel, Gregory W Berbusse, and Kari Naylor
BMC Research Notes, in press
Background
Mitochondrial morphology is maintained by two distinct membrane
events -fission and fusion. Altering these conserved processes can
disrupt mitochondrial morphology and distribution, thereby
disrupting the organelle’s functionality and impeding cellular
function. In higher eukaryotes, these processes are mediated by
a family of dynamin-related proteins (DRP’s). In the lower
eukaryotes, for instance Dictyostelium discoideum, mitochondrial
fission and fusion have been implicated but not yet established.
To understand the overall mechanism of these dynamics across
organisms, we developed an assay to identify fission and fusion
events in Dictyostelium and to assess the involvement of the
mitochondrial proteins, MidA, CluA, and two DRP’s, DymA
and DymB.
Findings
Using laser scanning confocal microscopy we show, for the first t
ime, that lower eukaryotes mediate mitochondrial fission and fusion.
In Dictyostelium, these processes are balanced, occurring
approximately 1 event/minute. Quantification of the rates in midA-,
cluA-, dymA-, or dymB- strains established that MidA appears to
play an indirect role in the regulation of fission and fusion, while the
DRP’s are not essential for these processes. Rates of fission and
fusion were significantly reduced in cluA-cells, indicating that CluA
is necessary for maintaining both fission and fusion.
Conclusions
We have successfully demonstrated that Dictyostelium mitochondria
undergo the dynamic processes of fission and fusion. The classical
mediators of membrane dynamics - the DRP’s – are not necessary
for these dynamics, whereas CluA is necessary for both processes.
This work contributes to our overall understanding of mitochondrial
dynamics and ultimately will provide additional insight into
mitochondrial disease.
Submitted by Kari Naylor [[log in to unmask]]
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[End dictyNews, volume 38, number 23]
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