Research reveals fruit fly circadian clock mechanisms

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Drosophila melanogaster feeding on bananas. Credit: Wikimedia Commons, CC BY-SA 4.0

The higher the temperatures, the faster the physiological processes. But there is one exception: the so-called circadian clock, which regulates the sleep-wake cycle in organisms. A fascinating question for scientists is why the internal clock works almost unchanged despite fluctuations in temperatures. This is a phenomenon known as temperature compensation. Studies show that different molecular mechanisms contribute to this.

Prof. from the University of Münster (Germany). A team of biologists led by Ralf Stanewsky and in collaboration with teams at Dalhousie University in Canada and the University of Mainz in Germany have now found an important piece of the puzzle. this question. The results of their work were published in the journal Current Biology.

The team discovered a point mutation in the fruit fly Drosophila melanogaster that causes the circadian clock periods to be prolonged due to temperature. It resides in a central “clock gene” known as a “period” (per). Flies with this perI530A mutation exhibit a normal 24-hour sleep-wake rhythm at 18 degrees Celsius. In contrast, at 29 degrees Celsius, the internal clock runs about five hours slower, i.e. it takes 29 hours. This period prolongation also affects the expression, that is, the activity of the period gene in clock neurons in the brain.

Normally, the protein of interest (PERIOD) is gradually changed chemically over 24 hours – specifically phosphorylated. It degrades after maximum phosphorylation. Here, too, this process is normally the same at temperatures between 18 and 29 degrees Celsius, where fruit flies are active. As the researchers showed, phosphorylation occurs normally at 18 degrees Celsius in the perI530A mutant, but decreases as the temperature increases. This leads to stabilization of the “PERIOD” protein at higher temperatures.

The mutation studied by the team affects a so-called nuclear export signal (NES), which also appears in this form in mammalian period genes and is involved in the transport of PERIOD proteins out of the cell nucleus. No biological function of this export from the cell nucleus was previously known. The current study shows that the mutation leads to prolonged retention of the PERIOD protein in the cell nucleus of central clock neurons, again only at higher temperatures. “Therefore,” says Ralf Stanewsky, “we hypothesize that protein export from the cell nucleus plays an important role in temperature compensation, at least in the case of the fruit fly.”

Scientists used fruit fly mutants with changes in the period gene (perI530A) produced by modern molecular genetic methods (CRISPR/Cas9 mutagenesis and homologous recombination). These animals were then tested to see if their sleep-wake cycles and consequently their running activities differed depending on the ambient temperature.

Using a variety of methods, the researchers visualized clock genes and their activity in brain neurons. One of the things they used was a new method called Locally Activated BioLuminescence (LABL), which the Münster team developed in collaboration with researchers in Canada. This method, involving bioluminescence, makes it possible to measure rhythmic gene expression in clock neurons, which make up only a fraction of all brain neurons, in living flies.

More information:
Astrid Giesecke et al., a novel epoch mutation involving nuclear export in the temperature compensation of the Drosophila circadian clock, Current Biology (2022). DOI: 10.1016/j.cub.2022.12.011

Provided by the University of Münster

Quotation: Research reveals fruit fly circadian clock mechanisms (2022, 29 Dec) retrieved from on December 30, 2022

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