A so-called clock gene linked to the natural 24-hour cycle of all earthly organisms is so exquisitely sensitive that its expression varies in response to light, report Salk Institute for Biological Sciences researchers in a study published today in the Proceedings of the National Academy of Sciences.
The findings add to our understanding of the circadian clock, a mysterious mechanism that operates in in individual cells as well as entire physiological systems, setting the internal pace of the lowest fungi and highest mammals.
Eating, sleeping, hormone production and brain activity are all guided by circadian rhythyms. Insomnia and depression are among the conditions thought to arise when we miss a beat. But despite the clocks’ ubiquity, scientists are still trying to make sense of the pieces.
In the study, the researchers trained a light on skin cells hacked with a bioluminescent marker that glowed in response to Per2 gene activation. Mutations in Per2 have been associated with a condition called familial advanced sleep phase syndrome, in which people feel sleepy early in the evening and wake up in what is for other people the middle of the night.
They found that the gene expressed itself strongly under light; with the light off, the gene went to sleep.
What does this mean? The researchers drew no conclusions, and the study was not designed to connect the phenomena to physiological outcomes.
But it does hint at the marvelous sensitivity of the circadian system, and suggests that we should look more closely at the effects of modern lifestyles on that system.
The observations called to mind a study I came across two years ago, in which artificial light stimulated breast cancer growth in mice — findings that were loosely echoed in studies of night shift workers. Other research has attributed therapeutic effects to natural light.
Such findings are so far limited, and hampered by variabilities in study design and measurements — but it’s worth noting that things like night shifts and artificial light are wholly novel in human development, having emerged in the last century and interacting with systems that evolved for millions of years in harmony with unchanging natural cycles.
Reciprocity between phase shifts and amplitude changes in the mammalian circadian clock [PNAS]
Image: Alexandre Duret-Lutz
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