Universal mechanism behind day-night rhythm

The condition of the enzyme peroxiredoxin is part of a universal mechanism for the 24-hour rhythm in all forms of life. This is the first time that a day-night rhythm system has been discovered, which is present in practically all organisms. The discovery was made by researcher Maria Olmedo and Professor of Molecular Chronobiology Martha Merrow of the University of Groningen, together with scientists from Great Britain and the United States. The findings are published 16 May 2012 in the journal Nature.

Nearly all living cells operate according to a 24-hour, circadian rhythm. This day-night rhythm is assumed to date back to the very the beginning of life; after all, day and night have always existed. Mechanisms supporting the rhythm (known as clock genes) have been found in various organisms. Up until now, the clock system appeared to be unique to the specific task of the organism.

The peroxiredoxin enzyme has now enabled researchers to uncover a system that goes back much further into the evolution of the circadian rhythm. The scientists examined representatives of all the main groups of organisms: mice, plants (thale cress, Arabidopsis thaliana), fruit flies (Drosophila melanogaster) and prokaryotes (Synechococcus elongatus and Halobacterium salinarum). The researchers from Groningen studied the filamentous fungus Neurospora crassa.

Peroxiredoxin

The anti-oxidizing effect of the enzyme peroxiredoxin plays an important part in protecting cells; it neutralizes the free radicals that damage the DNA and accelerate the ageing process of the cells. Enzymal activity depends on the oxidative condition of the enzyme. Olmedo examined the oxidative condition of the peroxiredoxin enzyme in Neurospora crassa by growing the fungus in complete darkness. She discovered a 24-hour pattern with oxidation peaks during the day, as did her colleagues studying other organisms.

Evolution

According to Olmedo, it is no surprise that an anti-oxidizing enzyme has been found to be part of this universal mechanism. Olmedo: ‘Approximately 2.5 billion years ago, bacteria responsible for photosynthesis caused an explosive rise in the oxygen level in the air (Great Oxidation Event). The organisms that used oxygen for metabolism were at an advantage. But breathing oxygen also generates free radicals. Metabolism is often linked to a day-night rhythm. So what we are suggesting is that the organisms capable of responding to this fixed rhythm also had an evolutionary advantage. They were in a better position to repair the damage caused by using oxygen, and therefore able to adapt their physiology to the new conditions. Peroxiredoxin activity is probably a manifestation of a basal mechanism like this.’

Common origins

Scientists do not agree on the issue of whether ‘clock systems’ in different domains of life evolved independently of each other or have a common ancestor. These research findings make a significant contribution to this ongoing discussion, says Olmedo: ‘The lack of a universal circadian system would seem to support the independent evolution theory. However, our results now make it plausible that cellular rhythms do have common origins.’

Jetlag

Research into the mechanisms governing the circadian rhythm are currently in the spotlight, continues Olmedo: ‘It is becoming increasingly clear that interfering with the day-night rhythm (as in the case of jetlag or working night shifts) damages our health and is putting a financial strain on the health service. It is therefore essential to unravel the mysteries of the mechanisms behind the circadian rhythm.’ Chronobiological research at the University of Groningen is carried out at behavioural, physiological and molecular levels.

More information:

Prof. dr. Martha Merrow
Dr. Maria Olmedo, e-mail: maria.olmedo med.uni-muenchen.de

Refentie: Peroxiredoxins are conserved markers of circadian rhythms. Auteurs: Rachel S. Edgar, Edward W. Green, Yuwei Zhao, Gerben van Ooijen, Maria Olmedo, Ximing Qin, Yao Xu, Min Pan, Utham K. Valekunja, Kevin A. Feeney, Elizabeth S. Maywood, Michael H. Hastings, Nitin S. Baliga, Martha Merrow, Andrew J. Millar, Carl H. Johnson, Charalambos P. Kyriacou, John S. O’Neill, Akhilesh B. Reddy. Nature, 16 mei 2012, http://dx.doi.org/10.1038/nature11088