Publication Date

Summer 2016

Advisor(s) - Committee Chair

Dr. Sigrid Jacobshagen (Director), Dr. Claire Rinehart, and Dr. Ajay Srivastava

Degree Program

Department of Biology

Degree Type

Master of Science

Abstract

Circadian clocks are biochemical mechanisms that allow eukaryotic and some prokaryotic organisms to coordinate their physiology with daily environmental changes. It enables organisms to increase their fitness by taking advantage of beneficial environmental conditions while also avoiding or restricting certain sensitive processes during harsh conditions. Similarly, post-translational histone modifications allow eukaryotic organisms to regulate gene expression in response to environmental or developmental factors. Some post-translational modifications of histones are associated with active transcription while others are associated with repressed transcription depending upon the location, type and degree of modification. Trimethylation of lysine 4 on the N-terminal tail of histone H3 (H3K4me3) near a gene's promoter has been linked to active transcription of that gene in several organisms. The purpose of the current study was to investigate whether the amount of H3K4me3 at promoters of three specific genes shows a circadian rhythm in Chlamydomonas reinhardtii, a unicellular green alga. Two of the genes had previously been shown to display a circadian rhythm of expression with opposite phase (LHCBM6 and JMJD6-like2), while the third gene is constitutively expressed (RACK1). Quantitative PCR was used to determine the amount of immunoprecipitated H3K4me3 over a circadian cycle. It was hypothesized that H3K4me3 amount at the JMJD6-like2 and LHCBM6 promoter would show a circadian rhythm with a phase correlating directly with the phase of each gene’s rhythm of expression. Conversely, the H3K4me3 amount at the RACK1 promoter was predicted to not show a circadian rhythm, as the gene is constitutively expressed. Instead, results showed that H3K4me3 amount exhibits a circadian rhythm with identical phase for all three genes. ANOVA confirmed that the rhythms were not significantly different between the three genes. General histone H3 amount at promoters did not show a circadian rhythm across any of the three genes. Since recent genome-wide studies in mouse liver revealed a circadian rhythm of H3K4me3 amount with identical phase at the promoter of many genes with diverse expression, the findings presented here suggest that C. reinhardtii might show a similar global regulation of rhythmic H3K4me3 as in mice and that, therefore, this feature has been preserved during eukaryotic evolution.

Disciplines

Molecular Biology | Plant Biology | Plant Sciences

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