Date of Award

12-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Robert Hinrichsen, Ph. D.

Second Advisor

David Pistole, Ph. D.

Third Advisor

Paul Nealen, Ph. D.

Abstract

Circadian rhythms take place over the course of 24 hours, and ultradian rhythms are categorized as anything less than 24 hours. The recently discovered mutation of the shaggy gene in Drosophila has been shown to display disrupted circadian characteristics. The mammalian ortholog of shaggy is glycogen synthase kinase 3β (GSK-3β) a serine/ threonine kinase ubiquitously expressed in nearly every known eukaryote. Decreased function of this kinase through pharmacological and genetic means causes the circadian molecular oscillator to be phase delayed. Overexpression on the other hand, causes a phase advance in the 24 hour rhythm. This study sought to understand the relationship of GSK-3β/shaggy to the biological rhythms of the single celled organism Paramecium tetraurelia. This particular organism is known to display both ultradian and circadian rhythms that affect the frequency of the avoiding response. Lithium chloride, a drug most often used as a therapeutic agent, has been found to disrupt both ultradian and circadian rhythms. It is known to inhibit two enzymes, inositol monophosphatase and GSK-3β. The goal of this research project was to determine if the inhibition of GSK-3β by lithium chloride is what disrupts the circadian rhythm. In the present study it was found that inhibition of GSK-3β by indirubin caused a phase delay in the periodicity of the circadian rhythm in P. tetraurelia. To substantiate these observations, the gene was cloned and RNA interference was performed to decrease the levels of mRNA for GSK-3β in the cells. Decreased GSK-3β gene function also produced a phase delay of 3 hours. The results of this study did not suggest GSK-3β is involved in ultradian rhythmicity. At the same time, the findings of this study indicate GSK-3β is involved in the regulation of the circadian rhythms in Paramecium.

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