Circadian cycle even more important to life than previously suspected: study

Sep 12, 2011

Researchers at USC were surprised recently to discover just how much the rising and setting of the sun drives life on Earth – even in unexpected places.

Their findings, which appear this month in the Proceedings of the National Academy of Sciences, "speak volumes to the evolution of ," according to USC scientist Andrew Y. Gracey.

"Everything is tied to the rotation of the planet," he said.

In all organisms, a certain amount of gene expression (the process by which products are created from the blueprint contained in genes) is rhythmic. In creatures that live on land, that rhythm is unsurprisingly tied to the 24-hour day, known as the .

Mussels – which Gracey chose to study – instead spend their entire lives in dark shells in an area between the land and the sea, submerged or exposed depending on the tide.

Most of their physical activity is based on the tidal cycle; when mussels are exposed to the air, they close their shells and switch to an anaerobic metabolism, starving for oxygen, and when submerged they breathe and feed.

"It's a really profound change in their biology as they go from sea to land," said Gracey, assistant professor of biological sciences at the USC Dornsife College of Letters, Arts and Sciences.

One would expect, then, that the tidal cycle would be the clock that drives their gene expression. But in fact, as Gracey's tests discovered, while a "tidal clock" probably does exist for mussels, the lion's share of their is instead driven by the circadian cycle.

"The circadian cycle is trumping the tidal cycle," Gracey said.

Gracey and USC graduate student Kwasi Connor constructed an aquarium with an artificial tide by pumping water in and out every six hours. For four days straight, Connor collected samples every two hours – getting excellent data, but not much sleep.

"That's why this paper is so good; we have such a high resolution," Gracey said.

Connor shrugged off the sacrifice in the name of science: "It's critical that you get up and do measurements in a precise manner, otherwise you lose the value of the data," he said.

Later, Gracey and Connor ran a similar simulation in a more natural environment by suspending cages of mussels off of a dock, this time for 50 hours.

The results were unexpected. Of the genes that showed rhythmic expression, between 80 and 90 percent were driven by the circadian cycle.

Explore further: Oregon food label measure headed for recount

Related Stories

Team creates math model for circadian rhythm

Aug 27, 2007

The internal clock in living beings that regulates sleeping and waking patterns -- usually called the circadian clock -- has often befuddled scientists due to its mysterious time delays. Molecular interactions that regulate ...

Chronic drinking can disrupt circadian rhythms

Aug 24, 2010

Circadian rhythmicity is regulated by circadian clock genes, and animal studies have shown that chronic drinking can alter expressions in these genes. A new study has found that significantly lower levels of messenger ribonucleic ...

Scientists find clue to mystery of biological clock

Nov 30, 2009

How does our biological system know that it is supposed to operate on a 24-hour cycle? Scientists at the Hebrew University of Jerusalem have discovered that a tiny molecule holds the clue to the mystery.

Recommended for you

Parasitic worm genomes: largest-ever dataset released

17 hours ago

The largest collection of helminth genomic data ever assembled has been published in the new, open-access WormBase-ParaSite. Developed jointly by EMBL-EBI and the Wellcome Trust Sanger Institute, this new ...

Male sex organ distinguishes 30 millipede species

17 hours ago

The unique shapes of male sex organs have helped describe thirty new millipede species from the Great Western Woodlands in the Goldfields, the largest area of relatively undisturbed Mediterranean climate ...

How can we avoid kelp beds turning into barren grounds?

21 hours ago

Urchins are marine invertebrates that mould the biological richness of marine grounds. However, an excessive proliferation of urchins may also have severe ecological consequences on marine grounds as they ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Isaacsname
not rated yet Sep 13, 2011
Maybe I'm somewhat jaded , but I thought this was already kind of a no-brainer.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.