New insight into the circadian clock of Drosophila melanogaster.
The higher temperatures the higher the temperature, the more rapid the physiological processes happen. However, there’s a lone exception known as the circadian clock that regulates the sleep-wake cycles in living things.
The most interesting question for researchers is why the internal clock functions in a way that is almost constant regardless of fluctuations in temperature. This is a phenomenon referred to as “temperature compensation”.
Studies have shown that various molecular mechanisms play a role in this. A biologists’ team, led by prof. Ralf Stanewsky from the University of Munster (Germany) as well as in collaboration with researchers from Dalhousie University in Canada and the University of Mainz in Germany are now able to identify an important piece of the puzzle that provides the answer to this question. Their research is published in the publication “Current Biology”.
The team discovered a point mutation in the fruit fly Drosophila melanogaster which leads to a temperature-dependent lengthening of circadian clock periods. It’s located in a central “clock gene” known as”period” (per) “period” (per). The flies that have this mutation show an average sleep-wake pattern that lasts for 24 hours at an average temperature of 18. Celsius.
The protein in question (PERIOD) is slowly altered chemically over the course of 24 hours, and specifically that it is processed by phosphorylation. When phosphorylation is at its highest, it’s broken down.
In this, too, the procedure is usually the same for temperatures between 18 to 29 degrees Celsius where fruit flies are in active. As the research team discovered, the process of phosphorylation takes place in a normal manner in the perI530A mutation at 18 degrees Celsius but it decreases as temperature rises. This causes a stabling of”PERIOD,” the “PERIOD” protein at warmer temperatures.
The mutation that was studied by the group affects the nuclear export signal (NES) and is present within the period gene of mammals . It is involved in the transport of the PERIOD proteins from the nucleus of cells.
The biological significance of this transfer of the cell nucleus has been previously known. This study reveals that the mutation results in a prolonged preservation of the PERIOD protein within the nucleus of the central clock’s cell neurons, and this time just at temperatures higher.
“We therefore assume,” says Ralf Stanewsky “that the export of the protein from the cell nucleus plays an important role in temperature compensation – at least as far as the fruit fly is concerned.”
In their studies they employed fruit fly mutants that had an alteration in the gene for period (perI530A) that they created by using modern molecular genetics techniques (CRISPR/Cas9 Mutagenesis and homologous Recombination).
The animals were then examined to determine if their sleep-wake cycles – and, in turn, their running activity varied, based on the temperature of the surroundings. Utilizing a variety of techniques that they used, researchers were able to see the genes that regulate clocks and their activity within the brain’s neurons.
One of the methods they utilized was a brand new method known as Locally Activatable BioLuminescence (LABL) that the Munster team developed with the help of researchers from Canada. This technique involving bioluminescence allows them to observe, in live fly larvae, the frequency of gene expression in the clock neurons which represent a tiny fraction of brain cells.