Abstract
Sleep is an essential behavior, but the molecular mechanisms which regulate sleep remain unclear. The sleep of Drosophila melanogaster shares many key features with mammalian sleep, including homeostatic regulation and similar pharmacology. In Drosophila, ubiquitous inhibition of the microRNA let-7 has been linked to a reduced sleep phenotype. MicroRNAs are short, non-coding RNAs which control a variety of biological functions by negatively regulating gene expression. Within the nervous system, microRNAs play a role in the differentiation of neurons and glia, two cell types involved in sleep regulation. In this study, we utilized microRNA sponges under the control of tissue-specific promoters to inhibit let-7 function and characterize where and at what point during the life cycle let-7 functions to regulate sleep. Neuronal inhibition of let-7 resulted in decreased sleep during the day and night, and hyperactivity during the day. Restoration of let-7 function to the mushroom bodies rescued these daytime effects on sleep and activity. Expression of the let-7 sponge in animals during only development and only adulthood produced differential effects, where inhibition of let-7 pre-eclosion decreased daytime sleep while inhibition post-eclosion reduced nighttime sleep. We propose a model in which prior to eclosion, let-7 acts in the mushroom bodies to promote daytime siesta sleep and inhibit daytime activity in adult flies, but post-eclosion, let-7 functions in other neurons outside of the MB for proper nighttime sleep regulation in adults. These findings further our understanding of sleep and may later be applicable to studies of human sleep and sleep disorders.