Establishing Molecular Links Within a Systems-level Model of the Drosophila Sleep Homeostat

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Non-technical abstractThe intense sleep need felt the day following a night of sleeplessness is familiar to many. The build-up of this need is often urgent because sleep is crucial to many essential physiological processes including learning, memory formation and tissue repair. The increased sleep need is generated in the brain, presumably by a collection of neurons inter-connected via complex electrical and biochemical signals. This system of connected neurons is collectively known as the sleep homeostat. But despite the homeostat's central role in controlling sleep, very little is known about its structure, composition, and principles of operation. This research will construct a functional architecture of the homeostat by taking advantage of the fruit fly that, like humans, exhibits sleep but, owing to its relative simplicity offers a tractable system in which to dissect the homeostat. The proposed studies will develop a new series of genetic tools that will allow precise and controllable manipulations of the neurons and the interconnecting pathways suspected of forming the sleep homeostat. The experiments will be guided by a novel computational model developed by the PI. Results from the studies will constitute the first computational-molecular model of the sleep homeostat and will likely give rise to new testable hypotheses about the regulation of sleep-wake cycles. The interplay of mathematical modeling and genetics in the project will offer unique opportunities in interdisciplinary research and coursework for undergraduate and graduate students, with particular emphasis on involving members traditionally underrepresented in the sciences. Technical abstractThis work will establish a model of the sleep homeostat, a feedback system that adjusts future sleep need based on past sleep, which is both mathematically rigorous and molecularly tractable. The project will exploit the fruit fly to build upon a recently developed theoretical model that suggests that four core biochemical pathways constitute the homeostat of the insect. Parameters of the model predict that neuromodulators such as dopamine and short neuropeptide F describe these pathways. A combination of behavioral, genetic and computational approaches will be employed to link the theoretical parameters to the neuromodulators, thus establishing the first quantitative model of the sleep homeostat with well-defined molecular identities. Objective 1 will examine the sleep-wake dynamics over- or under-expressing candidate neuromodulators to rapidly generate a short-list of neuromodulator pathways. Objective 2 will then use the Gal4/UAS system to target the neuromodulator-producing neurons, biochemically perturbing them by altering the abundance of the short-listed substrates. Objective 3 will overexpress ion channels to electrically perturb specific neuromodulator-expressing neurons and serve as a third independent test in the identification of neuromodulators that underlie fly sleep homeostasis. Together, these studies will lead to a unified, computational-molecular model of the homeostat and, in so doing, substantially broaden our understanding of the neural mechanisms governing sleep. Additionally, the computational and molecular approaches taken in the research will be incorporated into laboratory experiences for students, thus training future scientists in how to integrate mathematical and molecular approaches in the study of nervous system functions.