Misregulation of Drosophila Myc Disrupts Circadian Behavior and Metabolism.

Drosophila Myc (dMyc) is highly conserved and functions as a transcription factor similar to mammalian Myc. We previously found that oncogenic Myc disrupts the molecular clock in cancer cells. Here, we demonstrate that misregulation of dMyc expression affects Drosophila circadian behavior. dMyc overexpression results in a high percentage of arrhythmic flies, concomitant with increases in the expression of clock genes cyc, tim, cry, and cwo. Conversely, flies with hypomorphic mutations in dMyc exhibit considerable arrhythmia, which can be rescued by loss of dMnt, a suppressor of dMyc activity. Metabolic profiling of fly heads revealed that loss of dMyc and its overexpression alter steady-state metabolite levels and have opposing effects on histidine, the histamine precursor, which is rescued in dMyc mutants by ablation of dMnt and could contribute to effects of dMyc on locomotor behavior. Our results demonstrate a role of dMyc in modulating Drosophila circadian clock, behavior, and metabolism.

A Conserved Circadian Function for the Neurofibromatosis 1 Gene.

Loss of the Neurofibromatosis 1 (Nf1) protein, neurofibromin, in Drosophila disrupts circadian rhythms of locomotor activity without impairing central clock function, suggesting effects downstream of the clock. However, the relevant cellular mechanisms are not known. Leveraging the discovery of output circuits for locomotor rhythms, we dissected cellular actions of neurofibromin in recently identified substrates. Herein, we show that neurofibromin affects the levels and cycling of calcium in multiple circadian peptidergic neurons. A prominent site of action is the pars intercerebralis (PI), the fly equivalent of the hypothalamus, with cell-autonomous effects of Nf1 in PI cells that secrete DH44. Nf1 interacts genetically with peptide signaling to affect circadian behavior. We extended these studies to mammals to demonstrate that mouse astrocytes exhibit a 24-hr rhythm of calcium levels, which is also attenuated by lack of neurofibromin. These findings establish a conserved role for neurofibromin in intracellular signaling rhythms within the nervous system.

AKT and TOR signaling set the pace of the circadian pacemaker.

The circadian clock coordinates cellular and organismal energy metabolism. The importance of this circadian timing system is underscored by findings that defects in the clock cause deregulation of metabolic physiology and result in metabolic disorders. On the other hand, metabolism also influences the circadian clock, such that circadian gene expression in peripheral tissues is affected in mammalian models of obesity and diabetes. However, to date there is little to no information on the effect of metabolic genes on the central brain pacemaker which drives behavioral rhythms. We have found that the AKT and TOR-S6K pathways, which are major regulators of nutrient metabolism, cell growth, and senescence, impact the brain circadian clock that drives behavioral rhythms in Drosophila. Elevated AKT or TOR activity lengthens circadian period, whereas reduced AKT signaling shortens it. Effects of TOR-S6K appear to be mediated by SGG/GSK3beta, a known kinase involved in clock regulation. Like SGG, TOR signaling affects the timing of nuclear accumulation of the circadian clock protein TIMELESS. Given that activities of AKT and TOR pathways are affected by nutrient/energy levels and endocrine signaling, these data suggest that metabolic disorders caused by nutrient and energy imbalance are associated with altered rest:activity behavior.