The time of our lives: researchers identify ancient mechanism behind our body clocks
27 January 2011
The circadian clock is vitally important to many forms of life and controls patterns of daily and seasonal activity, from sleep patterns to butterfly migrations to the opening of flowers. It has long been assumed that the circadian clock is linked to DNA or gene activity, but the new studies show that this is not so.
The first study, from the University of Cambridge's Institute of Metabolic Science, has identified for the first time 24-hour rhythms in red blood cells. Unlike most other cells in the body, red blood cells do not contain any DNA.
The research involved incubating purified red blood cells from healthy volunteers in the dark at body temperature, and sampling them at regular intervals for several days. The team examined the levels of biochemical markers - proteins called peroxiredoxins - that are produced in blood at high levels, and found that they underwent a 24-hour cycle. Peroxiredoxins are found in almost all known organisms.
Dr Akhilesh Reddy, lead author of the study, says: "We know that clocks exist in all our cells: they're hard-wired into the cell. Imagine what we'd be like without a clock to guide us through our days. The cell would be in the same position if it didn't have a clock to coordinate its daily activities.
"The implications of this for health are manifold. We already know that disrupted clocks - for example, caused by shift work and jet lag - are associated with metabolic disorders such as diabetes, mental health problems and even cancer. By furthering our knowledge of how the 24-hour clock in cells works, we hope that the links to these disorders - and others - will be made clearer."
The second study, by scientists from the Universities of Edinburgh and Cambridge and the Observatoire Océanologique in Banyuls, France, found a similar 24-hour cycle in marine algae, indicating that internal body clocks have always been important, even in ancient forms of life.
The researchers found evidence of circadian rhythms by sampling the peroxiredoxins in algae at regular intervals over several days. When the algae were kept in darkness, no DNA activity was observed, but the algae kept their circadian clocks ticking. Scientists had thought that the circadian clock was driven by gene activity, but both the algae and the red blood cells kept time without it.
Professor Andrew Millar from the University of Edinburgh's School of Biological Sciences, who led the second study, explains: "This groundbreaking research shows that body clocks are ancient mechanisms that have stayed with us through a billion years of evolution. They must be far more important and sophisticated than we previously realised. More work is needed to determine how and why these clocks developed in people - and most likely all other living things on Earth - and what role they play in controlling our bodies."
Additional funding for the studies was provided by the Biotechnology and Biological Sciences Research Council, the Engineering and Physical Sciences Research Council, the Medical Research Council, the French Agence Nationale de la Recherche, and the National Institute of Health Research.
Image: The circadian clock controls sleep patterns, among other things. Credit: Steve Sawyer on Flickr
References
O'Neill JS, Reddy AB. Circadian clocks in human red blood cells. Nature 2011.
O'Neill JS et al. Circadian rhythms persist without transcription in a eukaryote. Nature 2011.