UC San Diego

Research in humans and other model organisms has established that the daily timing and amount of sleep are regulated by the circadian clock and sleep homeostasis respectively. In contrast to the circadian clock, the biological basis of how sleep homeostasis is regulated in the brain remains poorly understood. In this dissertation, I investigate the genetics and neuroanatomy of sleep homeostasis regulation using the model organism Drosophila melanogaster.

Building on previous work in our lab, I explored the nature of a rare population of sensory neurons (named ppk) whose activity has a privileged role in driving sleep homeostasis. I mapped where ppk neurons are located in the peripheral nervous system (PNS) and used a combination of thermogenetic behavioral studies and imaging to examine the neuroanatomical relationship between ppk and other previously described sleep homeostasis driving neurons. These results showed that neurons capable of driving waking and subsequent sleep need do not have cell bodies in the brain but instead localize to the ventral nerve cord and to the PNS.

To investigate putative postsynaptic effectors of ppk-driven sleep homeostasis I used thermogenetically-controlled sleep behavior and trans-synaptic mapping to identify and characterize neurons that satisfy predictions of a neural circuit model for sleep homeostasis. Further, I report evidence that suggests this sleep homeostasis circuitry could be part of the output of the circadian clock, which would mechanistically link how the clock and sleep homeostasis interact to determine the arousal state of the fly.

Through an unbiased forward genetic screen I identified a mutation in the Protein Kinase CKII subunit CKIIβ that has impaired sleep homeostasis. Using genetic complementation and rescue studies I show that two transcripts of CKIIβ are necessary and sufficient for sleep homeostasis. I also demonstrate that the CKIIβ mutant’s effect on sleep can be phenocopied by pan-neuronal expression of dominant-negative CKIIα, and I map this effect to circadian clock neurons. I also demonstrate that CKII is required for sleep-dependent associative memory formation. This study supports a novel role for a protein kinase in sleep homeostasis and suggests that dysregulation of circadian function can potentially impact the function of the homeostat.