Electronic Edition
Volume 34, number 17
June 4, 2010
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=========
Abstracts
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Developmental significance of cyanide-resistant respiration under
stressed
conditions: experiments in Dictyostelium cells
Kei Kimura,1 Hidekazu Kuwayama,2 Aiko Amagai 3 and Yasuo Maeda1*
1Department of Developmental Biology and Neurosciences, Graduate
School of Life Sciences, Tohoku University, Sendai 980-8578;
2Graduate School of Life and Environmental Sciences, University of
Tsukuba,
Tennoudai 1-1-1, Tsukuba-shi, 305-8572; and
3Department of Biomolecular Science, Graduate School of Life Sciences,
Tohoku University, Katahira 2-1-1, Aoba-Ku, Sendai 980-8577, Japan
Develop. Growth Differ., in press
We have previously reported that benzohydroxamic acid (BHAM), a potent
inhibitor of cyanide (CN)-resistant respiration mediated by
alternative oxidase
(AOX), induces formation of unique cell masses (i.e., stalk-like cells
with a
large vacuole and thick cell wall) in starved Dictyostelium cells.
Unexpectedly,
however, aox-null cells prepared by homologous recombination exhibited
normal development under normal culture conditions on agar, indicating
that BHAM-induced stalk formation is not solely attributable to
inhibition of
CN-resistant respiration. This also suggests that a series of
pharmacological
approaches in the field of life science has serious limitations. Under
stress
(e.g., in submerged culture), starved aox-null cells exhibited
slightly delayed
aggregation compared with parental Ax-2 cells; most cells remained as
loose
aggregates even after prolonged incubation. Also, the developmental
defects
of aox-null cells became more marked upon incubation for 30 min just
after
starvation in the presence of ≥1.75 mM H2O2. This seems to indicate
that CN-resistant respiration could mitigate cellular damages through
reactive
oxygen species (ROS), because AOX has a potential role in reduction of
ROS
production. Starved aox-null cells did not develop in the presence of
5 mM
KCN (which completely inhibited the conventional cytochrome-mediated
respiration) and remained as non-aggregated single cells on agar even
after
prolonged incubation. Somewhat surprisingly, however, parental Ax-2
cells
were found to develop normally, forming fruiting bodies even in the
presence
of 10 mM KCN. Taken together, these results suggest that CN-resistant
respiration might compensate for the production of ATP via oxidative
phosphorylation.
Submitted by Yasuo Maeda [[log in to unmask]]
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An invitation to die: Initiators of sociality in a social amoeba become
selfish spores
by Jennie J. Kuzdzal-Fick, David C. Queller, and Joan E. Strassmann
Department of Ecology and Evolutionary Biology, Rice University
Biology Letters, in press
Greater size and strength are common attributes of contest winners.
Even in social insects with high cooperation, the right to reproduce
falls
to the well-fed queens rather than to poorly fed workers. In
Dictyostelium
discoideum, formerly solitary amoebae aggregate when faced with
starvation, and some cells die to form a stalk which others ride up to
reach a better location to sporulate. The first cells to starve have
lower
energy reserves than those that starve later, and previous studies have
shown that the better-fed cells in a mix tend to form disproportionately
more reproductive spores. Therefore, one might expect that the first
cells to starve and initiate the social stage should act
altruistically and
form disproportionately more of the sterile stalk, thereby enticing
other
better-fed cells into joining the aggregate. This would resemble caste
determination in social insects, where altruistic workers are typically
fed less than reproductive queens. However, we show the opposite
result holds: the first cells to starve become reproductive spores,
presumably by gearing up for competition and outcompeting late
starvers to become prespore first. These findings pose the interesting
question of why others would join selfish organizers.
Submitted by Jennie Kuzdzal-Fick [[log in to unmask]]
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[End dictyNews, volume 34, number 17]
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