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dictyNews Volume 23 Number 02
Dicty News
Electronic Edition
Volume 23, number 2
July 16, 2004
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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Transcriptional Transitions During Dictyostelium Spore Germination
Qikai Xu, Miroslava Ibarra, Dana Mahadeo, Chad Shaw, Eryong Huang,
Adam Kuspa, David Cotter and Gad Shaulsky
Eukaryotic Cell, in press
Many protozoa form spores in response to adversity, so spore germination
is a key process in their life cycle. Dictyostelium discoideum sporulate
in response to starvation following a developmental program. Germination
is characterized by two visible changes, spore swelling and emergence of
amoeba from the spore capsule. Several studies have indicated that an
additional process termed spore activation is also required, but the
physiological changes that characterize the three phases are largely
uncharacterized. We used microarrays to monitor global transcriptional
transitions as a surrogate measure of the physiological changes that occur
during germination. Using two independent methods to induce germination,
we identified changes in mRNA levels that characterize the germination
process rather than changes that resulted from the induction method. We
found that germination is characterized by three transitions. The first
transition occurs during activation, while the spores appear dormant, the
largest transition occurs when swelling begins, and the third occurs when
emergence begins. These findings indicate that activation and swelling
are not passive occurrences, such as dilution of inhibitors or spore
rehydration, but active processes that are accompanied by dramatic events
of mRNA degradation and de-novo transcription. This finding confirms and
extends earlier reports that genes such as celA are regulated during spore
germination. We also found by mutation analysis that the unconventional
myosin gene myoI, which is induced during early germination, plays a role
in the maintenance of dormancy and in spore swelling. This finding
suggests that some of the observed transcriptional changes are required
for spore germination.
Submitted by: Gad Shaulsky [gadi@bcm.tmc.edu]
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The Size-complexity Rule
J. T. Bonner
EEB Department, Princeton University, Princeton, NJ 08544
Evolution, In press
It is widely accepted that bigger entities have a greater division of labor
than small ones and this is reflected in the fact that larger multicellular
organisms have a corresponding increase in the number of their cell types.
This rule is examined in some detail from very small organisms to large
animals, and plants and societies. Compared to other size-related rules, the
size-complexity rule is relatively rough and approximate, yet clearly it
holds throughout the whole range of living organisms, as well as for
societies. The relationship between size and complexity is analyzed by
examining the effects of size increase and decrease: size increase requires
an increase in complexity, while size decrease permits, and sometimes
requires, a decrease in complexity. Conversely, an increase or decrease in
complexity permits, but does not require changes in size. An especially
compelling argument for the close relation between size and complexity can
be found in size quorum sensing in very small multicellular organisms.
Submitted by: John Bonner [jtbonner@Princeton.EDU]
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[End Dicty News, volume 23, number 2]
