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Description:
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Avian circadian clocks are composed of a distributed network of neural and
peripheral oscillators . Three neural pacemakers , located in the pineal , the eyes , and the
hypothalamus , control circadian rhythms of many biological processes through complex
interactions with slave oscillators located throughout the body . This system , an
astonishing reflection of the life history of this diverse class of vertebrates , allows birds
to coordinate biochemical and physiological processes and harmonize them with a
dynamic environment . Much work has been done to understand what roles these
pacemakers have in avian biology , how they function , and how they interact to generate
overt circadian rhythms . The experimental work presented in this dissertation uses the
domestic chicken , Gallus domesticus , as a model to address these questions and carry
forward current understanding about circadian biology in this species . To do so , we
utilized a custom DNA microarray to investigate rhythmic transcription in cultured chick
pineal cells . We then sought to identify genes which might be a component of the pineal
clock by screening for rhythmic transcripts that are sensitive to a phase -shifting light
stimulus . Finally , we surgically removed the eyes or pineal from chickens to examine the roles of these extra -SCN pacemakers in regulating central and peripheral rhythms in
metabolism and clock gene expression .
Using these methods , we show that the oscillating transcriptome is diminished in
the chick pineal ex vivo , while the functional clustering of clock controlled genes is
similar . This distribution reveals multiple conserved circadian regulated pathways , and
supports an endogenous role for the pineal as an immune organ . Moreover , the
robustness of rhythmic melatonin biosysnthesis is maintained in vitro , demonstrating
that a functional circadian clock is preserved in the reduced subset of the rhythmic pineal
transcriptome . In addition , our genomic screen has yielded a list of 28 genes that are
candidates for functional screening . These should be evaluated to determine any
potential role they may have as a component of the pineal circadian clock . Finally , we
report that the eyes and pineal similarly function to reinforce rhythms in brain and
peripheral tissue , but that metabolism and clock gene expression are differentially
regulated in chick . |