Our internal biological rhythm, i.e., the internal clock, controls many physiological processes. It works 24/7 and occurs even in the absence of external triggers, such as changes in light or temperature.
The internal clock is located in humans in the hypothalamus. Due to this internal clock, we are most awake from morning until the end of the day.
Like humans, all animals have circadian rhythms. Using Drosophila, the small fly found on ripe fruit, scientists at the University of Geneva studied the mechanisms that regulate these internal clocks. Many genes of Drosophila are conserved between the fly and higher organisms. This makes it possible to extend the scope of discoveries from fruit flies to humans.
Scientists used infrared sensors to detect the movements of flies movements in tubes to analyze their sleep-wake cycles easily. Over 24 hours, flies sleep for about 10 hours at night, then are active all day, except for a nap of about 4 to 5 hours.
Scientists also observed flies with a deregulated sleep-wake cycle and whose particular area of the brain, called ‘mushroom bodies’ because of its characteristic shape, is damaged. They analyzed the expression of genes in this area of the brain of healthy Drosophila.
Blanca Lago Solis, a researcher in the Department of Genetics and Evolution, said, “We identified a gene, Nf1, whose expression fluctuates according to the sleep-wake phases of the fly: its expression increases when the flies are awake, while it decreases during their sleep.”
Biologists observed flies that weakly express this gene, regardless of the time of day, to confirm the link between this gene and the circadian rhythm. These flies are dysregulated and have much more sleep phases.
The NF1 protein is upstream of a regulatory cascade that triggers the release of calcium, which is necessary for the activation of neurons in the brain’s mushroom bodies. The expression of Nf1 causes a higher activity of neurons in this area of the brain during the day than at night, thus promoting daytime wakefulness. The human homolog of Nf1 is a gene that prevents the development of tumors in the nervous system.
Emi Nagoshi, Professor at the Department of Genetics and Evolution at the UNIGE Faculty of Science, said, “When a person carries a mutation in the Nf1 gene, they have neurofibromatosis, a common genetic disease that predisposes to the development of nervous system tumors. One of the symptoms of patients with neurofibromatosis is sleep disturbance, and it will be interesting to explore the potential role of Nf1 in this phenomenon.”
- Machado Almeida, P., Lago Solis, B., Stickley, L. et al. Neurofibromin 1 in mushroom body neurons mediates circadian wake drive through activating cAMP–PKA signaling. Nat Commun 12, 5758 (2021). DOI: 10.1038/s41467-021-26031-2