The inner clock is not only ticking in the head
Our sense of time is controlled by a biological clock, which is commonly believed to be found in the brain. However, more recent studies on fruit flies paint a more complex picture. A gene that represents the blueprint for a protein in the inner clock is then read at various parts of the body - from the head to the bristles on the wings. Researchers led by cell biologist Steve Kay of the Scripps Research Institute in San Diego investigated whether individual body parts of fruit flies (Drosophila, also known as fruit, fruit or vinegar flies) react to changes in the light/dark cycle. They found that the internal clock genes in each part of the body turned on and off in accordance with the external rhythm. Her hope is to find new strategies to better manage time changes after long plane trips and shift work, as well as seasonal depression. But to do that, they need information about the locations of "clock" tissues and cells, as well as a clear understanding of the genes and proteins that make up the biological cogs.
In order to find out how the genes for the circadian clock are controlled in fruit flies, the scientists linked the relevant per gene (for period) with the GFP gene (for green fluorescent protein) from jellyfish. When this construct is active, the corresponding body parts fluoresce.
Glowing occurred in all of the tissues cultured by the researchers, suggesting that clocks are ticking in many different places, not just the brain. With a normal alternation between light and dark, the head, chest and abdomen glowed in rhythm. The bioluminescence was particularly visible in chemosensory cells on the hair bases on legs and wings as well as on the antennae and on the trunk. At these points, the clocks self-synchronized in response to light stimuli. It is conceivable that the biological clocks regulate the flies' sense of smell and taste, just as they regulate the sensitivity to light and pain in mammals.
According to Kay, “our discovery confirms that biological clocks operate in many tissues outside of and independently of the brain. They are put by the light; this suggests that cells harbor new photoreceptors for us that are not involved in vision.”
Although the scientists consider that their results question the role of the brain as the sole coordinator of internal rhythms, they point out that the brain itself has a special function in fruit flies. It is the only organ in which the clock genes can keep the clock even without light stimuli.
"These results are important for understanding how the timing of cellular functions is resolved in complex organisms," says Christopher Platt, director of the National Science Foundation's (NSF) neuroscience program. "This advance demonstrates how basic research on a model system can directly impact fields as diverse as agriculture and human biology."
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