Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Biology

Date of Defense

11-17-2017

Graduate Advisor

Sam Wang

Co-Advisor

Michael Hughes

Committee

Aimee Dunlap

Lon Chubiz

Michael Hughes

Sam Wang

Abstract

Circadian clock is a transcriptional/translational feedback loop that drives the rhythmic expression of downstream mRNAs. Termed “clock-controlled genes,” these molecular outputs of the circadian clock orchestrate cellular, metabolic, and behavioral rhythms. As part of our on-going work to characterize key upstream regulators of circadian mRNA expression, we have identified a novel clock-controlled gene in Drosophila melanogaster, Achilles (Achl), which is rhythmic at the mRNA level in the brain and represses expression of immune response genes, especially anti-microbial peptides in the immune system. Achl knock-down in the brain dramatically elevates expression of crucial immune response genes, including IM1 (Immune induced molecule 1), Mtk (Metchnikowin), and Drs (Drosomysin). As a result, flies with knocked-down Achl expression are more resistant to bacterial challenges. Meanwhile, no significant change in core clock gene expression and locomotor activity is observed, suggesting that Achl influences rhythmic mRNA outputs rather than directly regulating the core timekeeping mechanism. Additionally, Achl knock-down in the brain disrupts the rhythmicity of the immune system. Flies with knocked-down Achl show altered rhythmicity in both survival towards infection and sensitivity of immune response gene induction upon infection. Using high-throughput RNA-sequencing, we also identified candidate clock controlled genes that are downstream of Achl. Notably, Achl knock-down in the absence of immune challenge significantly diminishes the fly’s overall lifespan and resistance towards starvation, indicating a behavioral or metabolic cost of constitutively activating this pathway. Together, our data demonstrate that (1) Achl is a novel clock-controlled gene that (2) regulates the immune system in a repressive manner. (3) Achl regulates the rhythmicity of the immune system, and (4) Achl participates in signaling from the brain to immunological tissues.

Available for download on Saturday, December 07, 2019

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