The circadian clock studies the molecular mechanisms that explain "temperature compensation."

The higher the temperature, the faster
the physiological process.
But there is one exception: the so-called circadian clock, which regulates the sleep-wake cycle
of an organism.

An interesting question for scientists is why the internal clock behaves
in an almost constant way, even when the temperature fluctuates.
This phenomenon is called temperature compensation
.
Studies have shown that different molecular mechanisms contribute to this phenomenon
.
A team of biologists led by Professor Ralf Stanewsky from the University of Münster (Germany), in collaboration with teams at Dalhousie University in Canada and the University of Mainz in Germany, have now identified an important piece of this puzzle and provided an answer
to this question.
Their findings were published in the journal Current Biology
.

The team found a point mutation in Drosophila melanogaster, which causes a temperature-dependent circadian clock cycle to lengthen.

It is located in
a central "clock gene" called the per.
Flies with this perI530A mutation showed a normal sleep-wake rhythm
for 24 hours at 18 degrees Celsius.
In contrast, at a temperature of 29 degrees Celsius, the biological clock is 5 hours slower, that is, it lasts 29 hours
.
The prolongation of the menstrual cycle also affects the expression of the menstrual cycle genes in the clock neurons of the brain, in other words, its activity
.

NORMALLY, THE ASSOCIATED PROTEIN (PERIOD) PROGRESSIVELY UNDERGOES CHEMICAL CHANGES OVER A 24-HOUR PERIOD – SPECIFICALLY, IT IS PHOSPHORYLATED
.
After maximum phosphorylation, it is degraded
.
Here, the process is usually the same between 18 and 29 degrees Celsius, at which the flies are active
.
As the researchers showed, phosphorylation of perI530A mutants occurs in a normal way at a temperature of 18 degrees Celsius, but decreases
with increasing temperature.
This results in the stabilization of the "PERIOD" protein at higher temperatures
.

The mutation the team studied affects the so-called nuclear output signal (NES), which also appears in mammalian cycle genes in this form and plays a role
in transporting the PERIOD protein out of the nucleus.
No one knew before about this biological function
exported from the nucleus.
The current study suggests that this mutation leads to prolonged retention of the PERIOD protein in the nuclei of central clock neurons — again, only at
higher temperatures.
Ralf Stanewsky said: "Therefore, we believe that exporting proteins from the nucleus plays an important role in temperature compensation – at least in the case of fruit flies
.
"

method

In their study, the scientists used fruit fly mutants
modified with periodic genes (perI530A) that they produced using modern molecular genetic methods (CRISPR/Cas9 mutagenesis and homologous recombination).
The animals were then tested to see if their sleep-wake cycles — and their activity — varied
with ambient temperature.
The researchers used a variety of methods to visualize
clock genes and their activity in neurons in the brain.
One of the methods they used is a new method called locally activated bioluminescence (LABL), which Münster's team developed
in collaboration with Canadian researchers.
This approach involving bioluminescence makes it possible to measure rhythmic gene expression in clock neurons, which make up only a small fraction
of all brain neurons.