Body clock mechanism found in all living organisms

Scientists at the University of Edinburgh and Cambridge have proposed a new mechanism for the control of the human 24-hour ‘body clock’.

People have known about the internal 24-hour circadian clock for centuries. It follows the Earth’s 24-hour rotational period and governs the time patterns of everything in nature, from flowering plants to migratory animals.

The internal clock has two key features: it is unaltered by temperature, and it can be trained by environmental stimuli such as light or eating habits.

New evidence published in the science journal Nature suggests a shared ancestor for the circadian clock across the animal kingdom, including humans and even single-celled organisms.

Scientists John O’Neill and Andrew Millar have indicated that DNA transcription, a copying mechanism found only in animal cells, is not essential for the maintenance of the circadian rhythms.

Before these discoveries, it was widely accepted that gene activity, which requires DNA transcription, maintained the rhythms of physiological functions. However, new evidence suggests that these clocks keep time even when DNA transcription no longer occurs.

Mr Millar and colleagues conducted experiments on red blood cells, which contain no DNA. They found that highly conserved proteins known as peroxiredoxins underwent 24-hour long cycles. Given that peroxiredoxins are found in almost all organisms, this hints at a shared common ancestor.

Supporting this, the University of Edinburgh’s Andrew Millar experimented on single celled algae by blocking all DNA activity. He found that 24-hour cycles continued in the absence of any transcriptional mechanisms.

Mr Millar also found that the 24-hour cycles continued even without external cues such as daylight. Rhythms also continued in darkness, when DNA is inactive.

The essential mechanisms for 24-hour rhythms occur after DNA activity. Mr Millar stated that these mechanisms are conserved across the animal and plant kingdoms, and thus represent the remains of an evolutionarily ancient clock from our common ancestors.

This work into 24-hour rhythms could have serious implications for the many health issues associated with disrupted internal clocks, such as mental health problems and diabetes.

Mr O’Neill has proposed further work exploring whether the protein peroxiredoxin can be used as a marker of circadian rhythms in all organisms or whether a specific ‘clock gene’ can be found in every organism that undergoes cyclical oscillations.

Understanding the exact mechanism through which these proteins confer rhythmic cycles is the next step in this expanding field of science.