2009-ASCB-Press-Book - page 4

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T h e A m e r i c a n s o c i e t y f o r C e l l B i o l o g y
News from
The American Society
for Cell Biology
49th Annual Meeting
San Diego, CA
December 5–9, 2009
Feeding like clockwork
EMBARGOED
FOR RELEASE
10:00 am, U.S. Pacific Time
Sunday, December 6, 2009
Contact
Amita Sehgal
University of Pennsylvania
Medical School
219 Stemmler Hall
Philadelphia, PA 19104
(215) 573-2985
Author presents
Sunday, December 6, 2009
9:35–9:55 am
Minisymposium 5: Clocks
Program 29
Room 31A–C
Cellular Basis of Rhythmic
Behaviors
A. Sehgal, K. Xu, J. DiAngelo
Neuroscience, University of
Pennsylvania School of Medi-
cine/HHMI, Philadelphia, PA
Appetite and consumption in fruit
flies is controlled by two sets
of circadian clockwork genes
working at cross purposes
T
oday we know that human clock-
work genes set the pace for many
of our body organs, such as the
liver, which has a clock that drives
rhythms in metabolic function. Circadian
clocks have been around for billions of
years. Even organisms at the roots of the
tree of life, such as bacteria, have clock-
work genes. However, an understanding
of 24-hour circadian clocks has dawned
on the world only in recent decades as
cell biologists began experimenting with
the fruit fly,
Drosophila melanogaster,
and discovered that its sleeping patterns
were controlled by 24-hour cycling genes.
One pioneer of the so-called sleep–wake
circadian genes was Amita Sehgal. Now a
Howard Hughes Medical Institute inves-
tigator at the University of Pennsylvania
Medical School, Sehgal has extended the
circadian clock repertoire into metabo-
lism with the discovery of two sets of
clockwork genes in fruit flies that work at
cross purposes. If
Drosophila
genes can
speak to the human condition, then Seh-
gal’s latest research shows that we feed by
conflicting clockwork.
The fat body in the fly is analogous
to the human liver, and the Sehgal lab
was interested in studying how circadian
rhythms drive feeding and metabolism by
charting expression levels of molecules
in the fat body that change over the day–
night cycle. These experiments led to the
identification of several molecules that
function in several different pathways,
including lipid metabolism, immune
response, and detoxification.
When looking at metabolic functions,
Sehgal and colleagues discovered that
both
Drosophila
appetite and consump-
tion are controlled by two rival sets of
clocks, one in neurons and the other in
the fly fat body. These clocks are at odds.
(This would be the equivalent of the
human liver and adipose tissue sending
conflicting messages.) In fruit flies, these
two tissues exert opposing effects on the
storage of nutrient reserves and thereby
on food consumption and the response to
starvation.
The clock in the fat body promotes
the storage of nutrients, thereby allowing
the animal to survive periods of starva-
tion. On the other hand, clocks in the ner-
vous system deplete nutrient stores and
promote feeding, most likely to replace
the nutrients consumed. Sehgal thus
concludes that the interaction of these
metabolic and neuronal clocks probably
controls a circadian rhythm of feeding.
The feedback, though, is compli-
cated, says Sehgal. “We have found that
metabolic signals, such as feeding, can
change the expression of some of these
molecules. Thus, clocks can drive rhythms
of metabolic function, and metabolic
signals can affect the clock.”
Drosophila appetite
and consumption
are controlled by two
rival sets of clocks,
one in neurons and
the other in the fly fat
body. These clocks are
at odds. In fruit flies,
these two tissues exert
opposing effects on
the storage of nutrient
reserves and thereby
on food consumption
and the response to
starvation.
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