The answer to the question “Why do we sleep?” lies in understanding the biological underpinnings of homeostatic drive to sleep. Wakefulness is correlated with numerous changes in brain activity, structure and gene/protein expression that re-normalize following sleep however which of these elements is sufficient to cause sleep drive and how this might be accomplished remains unclear. The circadian clock was originally thought to solely provide a timing cue for initiation of sleep however recent work has demonstrated that clock input modulates both behavioral and brain activity indicators of sleep homeostasis in mammals. As the genetics and neural circuits underlying circadian rhythms are well understood across species, we hypothesize that exploiting this link in the tractable Drosophila melanogaster would clarify what genes and activity patterns are necessary for determining homeostatic sleep drive.Here we create a novel timed sleep deprivation protocol coupled with genetic strategies to knockdown genes and ablate neurons to elucidate how the clock impacts the homeostatic drive to sleep. First, we demonstrate that circadian input through highly specific clock neurons enhances homeostatic signal in the morning and suppresses it in the evening much liked what is seen in mammals. We demonstrate that R5 ellipsoid body neurons that are necessary and sufficient for homeostatic sleep drive exhibit time dependent changes in gene expression, synaptic protein expression and calcium responsiveness to sleep deprivation. This suggests that clock neuron input creates morning/evening neuronal states that impact the sleep relevant output of this neuropil. To understand how ubiquitination proteins known for their impact on sleep and circadian rhythms may play a role in this process we examined how mutants of CULLIN3 adaptor proteins impact this phenomenon. We characterize a sleep phenotype in tango10 mutants and a circadian phenotype in insomniac mutants and localize their function in these behaviors to peptidergic circuitry. We also find that TANGO10 is acting in cholinergic neurons to regulate evening suppression of homeostatic sleep drive suggesting that this protein plays an important role in mediating morning/evening homeostatic states. Lastly we explored how light and photoresponsive CRYPTOCHROME impact homeostatic sleep drive. We determine that, in the absence of a functional circadian transcription feedback look and the presence of constitutively high CLK protein, light becomes the major determinant of rebound enhancement and suppression such that once again rebound is high in the morning and low at night. This effect is mediated by PDF neuron signaling. Interestingly we find an independent pathway acting through CRYPTOCHROME such that in its absence rebound is very high suggesting it suppresses rebound as well. This effect appears to be due to its action downstream of R5 neurons in the dorsal fan-shaped body a major sleep neuropil.

Creator

• Andreani-fabroni, Tomas Sergio

DOI

• https://doi.org/10.21985/n2-eg4t-vk39

Subject

• Neurosciences

Language

• en

Alternate Identifier

• etdadmin_upload_906530
• http://dissertations.umi.com/northwestern:16115

Keyword

• Circadian
• Homeostasis
• Sleep
• Drosophila
• Time

Date created

• 2022-01-01

Resource type

• Dissertation

Rights statement

• In Copyright