Sex differences in circadian output signaling

PROJECT SUMMARY/ABSTRACT Circadian rhythms are the backing track to the symphony of life. Circadian rhythms not only allow organisms to coordinate their behavior and physiology with daily and seasonal changes but also temporally coordinate internal processes across organ systems. However, genetic, molecular, circuit, metabolic, and behavioral studies of chronobiology have been conducted primarily in male animals. Although the overall architecture of circadian systems is conserved across phylogeny and between sexes, circadian systems are not identical between sexes. This proposal exploits the Drosophila melanogaster genetic model to identify sex differences in circadian output signaling from the brain clock to peripheral metabolic tissues. We have identified two major knowledge gaps: (1) Sex differences in circuitry and signaling from the brain clock to clock output regions that communicate time of day to peripheral tissues; and (2) Sex differences in peripheral responses to circadian entrainment at baseline and when exposed to clock desynchronizing stressors. Our published and preliminary data has identified sex differences in the role of specific clock output neuropeptides in regulating circadian behavior and shown that age and high-fat diet have separable effects on dampening circadian rhythms of locomotor behavior and peripheral gene expression. In Project 1, we will use in vivo and in silico circuit mapping techniques to identify how sex-specific circuitry interacts with circadian clock outputs, identify sex specific transcriptional programs that alter morphology, cell number, connections, and physiology of clock output neurons, and use CRISPR knockout screening to identify specific signaling molecules and cognate receptors that contribute to sexually dimorphic circadian output signaling. In Project 2, we will use a novel long-term circadian luminescence imaging approach to identify how circadian gene transcription rhythms break down in peripheral tissues in response to aging, high fat diet, and the confluence of these stressors in male vs. female flies. We will also focus on insulin signaling as a candidate clock output molecule entraining peripheral metabolic tissues and characterize sex differences in insulin release, peripheral responses to insulin, and insulin-dependent entrainment of peripheral gene expression at baseline, across the lifespan, and under conditions of nutritional stress including high-fat and high-sugar diets. By investigating neuronal physiology, specific signaling molecules, circuitry, and behavioral genetics, we will develop a complete picture of how sex- and mating-dependent differences in circadian behavior and peripheral physiology arise. These findings will provide important insights into behavioral circuit degeneracy – how sexually dimorphic circuitry provides very similar circadian output under standard conditions. In addition, we will reveal sexually dimorphism in how circadian physiology responds to aging and dietary stress. Understanding the fundamental biology of sex differences in circadian biology across lifespan and stressors will identify principles that allow us to leverage chronobiology to improve human health in more personalized ways.