A Conserved Circadian Function for the Neurofibromatosis 1 Gene

Abstract

SUMMARYLoss 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.

Molecular and circuit mechanisms mediating circadian clock output in the Drosophila brain

“…Restoring Nf1 in clock cells does not rescue the behavioral deficits. Instead, Nf1 is required broadly in the brain, presumably in multiple circadian neurons that regulate rest:activity rhythms (Bai et al., ). Not only does Nf1 regulate PDF levels in the s‐LNv projections, it regulates Ca 2+ and neuropeptide levels in circadian output neurons that are downstream of clock neurons (discussed below).…”

“…Ca 2+ cycling in Dh44 + neurons requires the Pdf + LNvs, suggesting that rhythmic Ca 2+ levels propagate from the s‐LNvs to Dh44 + neurons (Cavey, Collins, Bertet, & Blau, ). In addition, the Nf1 circadian output gene cell‐autonomously regulates Ca 2+ cycling in Dh44 + neurons (Bai et al., ).…”

Social behavioral deficits in NF1 emerge from peripheral chemosensory neuron dysfunction

“…In the absence of Nf1, hyperactive Ras might modulate ppk23 receptor expression levels or expression of other receptor complex components; alter excitability through phosphorylation-dependent post-translational modification of channels; or interfere with downstream signaling cascades ultimately affecting intracellular calcium. Indeed, previous work suggests a role for Nf1 in regulating intracellular calcium levels in Drosophila neurons and mammalian astrocytes (Bai et al, 2018). Furthermore, studies from isolated mouse dorsal root ganglion cells demonstrate changes to N-type calcium currents in Nf1+/-sensory neurons compared to controls, likely involving post-translational modification to these channels (Duan et al, 2014).…”

“…Together our data identify a specific circuit mechanism through which Nf1 acts to regulate social behaviors, and suggest social deficits in NF1 arise from propagation of sensory misinformation. and sleep abnormalities, learning and memory deficits, hyperactivity, and repetitive grooming behavior (The et al van der Voet et al, 2016;Bai et al, 2018). Disruption of the conserved signaling pathways downstream of Nf1, Ras-MAPK and/or cAMP-PKA, has been implicated in these phenotypes.…”

Hugin+neurons link the sleep homeostat to circadian clock neurons

“…Dh44-expressing neurons in the pars intercerebralis regulate locomotor activity rhythms in part through the signaling of DH44 neuropeptide to hugin-expressing neurons in the subesophageal zone (SEZ) (Cavanaugh et al, 2014;King et al, 2017). Dh44+ and hugin+ circadian output neurons do not contain canonical molecular clocks, but display cycling in neuronal activity or peptide release, likely under control of upstream circadian signals (Bai et al, 2018;Cavey, Collins, Bertet, & Blau, 2016;King et al, 2017). However, links between these neurons and loci regulating sleep homeostasis have not been identified yet.…”