In a world of supposedly random life, even muscles have their own clocks

passage of time, imaged/S. Sepp

Twenty years ago, we didn’t know that muscles had their own circadian clocks. They turn out to be important to health.

“Clock systems are a sort of core, primordial part of our genome that instruct and prepare cells for the work of using nutrients, moving around, breathing, and [other] fundamental processes,” says Joseph Bass, a clinical endocrinologist at Northwestern University. “This is a story that’s evolving across a lot of different experimental systems—and muscle is now a new experimental system on the block.” The study of circadian rhythms, the daily cycles that regulate tissue and cell function, was once focused primarily on the suprachiasmatic nucleus, the “master clock” in the brain. Beginning in the late 1990s, scientists began uncovering peripheral clocks—timekeepers located throughout the body—and in 2007, Esser, Takahashi, and their colleagues confirmed their presence in muscles… The muscle clock also appears to regulate the type of fuel that the cell burns. Although active tissues require more energy, cells still need some fuel during sleep, but rather than rely predominately on glucose, which powers contractile activity during waking hours, they burn lipids and amino acids while at rest. By examining mouse tissues at various time points, Schiaffino’s team observed that Bmal1 and its target gene, REV-ERBα, play a key role in this fuel selection process. “I think there has evolved a fairly clear picture that the clock is segregating . . . aspects of metabolism to fit with the rest and activity cycles of the day,” says Esser. DIANA KWON, “Muscle Clocks Play a Role in Regulating Metabolism” at The Scientist

Evolution, said to be entirely unintelligent, can even plan your day.

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