Roles for extra-hypothalamic oscillators in the avian clock

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Title: Roles for extra-hypothalamic oscillators in the avian clock
Author: Karaganis, Stephen Paul
Abstract: 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 .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2663
Date: 2009-05-15

Citation

Roles for extra-hypothalamic oscillators in the avian clock. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2663 .

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