Two interacting processes, the circadian clock and a homeostatic sleep drive, which reflects both the quality and quantity of waking experience, regulate sleep. The circadian clock has been heavily studied and the molecular process underlying it is well understood. The sleep homeostat, on the other hand, is poorly understood and our knowledge of the molecular processes governing it is incipient at best. Discovery of the gene period, which encodes an integral component of the molecular clock and displays oscillatory expression reflecting normal clock function, allowed for real-time monitoring of the clock's molecular mechanism in vivo using a bioluminescent luciferase reporter (per-luc). In contrast, the best marker of sleep drive is electroencephalogram delta band power, which neither completely reflects sleep drive nor serves as a functional component of the sleep homeostat. Thus, the primary goal of this project is to use a specific set of parameters defining an ideal homeostatic marker to actually identify markers of homeostatic sleep drive. Previous attempts to identify genes with a role in the sleep homeostat through transcriptomics have largely suffered from a lack of specificity. Substantial changes in gene expression can often be observed in specific circuits at times when global profiling reveals naught. This proposal leverages the Allada lab's expertise in gene expression profiling of small, genetically defined populations of neurons to identify transcripts that reflect changes in homeostatic drive in sleep relevant areas of the fly brain. In addition, I am proposing several novel strategies to improve detection of homeostatic genes by eliminating circadian influence and manipulating waking experience prior to homeostatically driven recovery sleep. Candidate transcripts will be subjected to secondary screening to eliminate genes that do not play a functional role in homeostatic drive. Finally, I propose to develop novel tools for in vivo monitoring of the molecular process governing sleep drive to facilitate future inquiry into the mechanisms underlying sleep.