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Biological functions governed by the circadian clock are the evident result of the entrainment operated by the earth’s day and night cycle on living organisms. However, the circadian clock is not unique, and cells and organisms possess many other cyclic activities. | MINIREVIEW Collective behavior in gene regulation Metabolic clocks and cross-talking Michele M. Bianchi Department of Celland DevelopmentalBiology University of Rome La Sapienza Italy Keywords circadian clock cross-talk cycles ergodic system message metabolism redox synchronization transcription dynamics ultradian clock Correspondence M. M. Bianchi Department of Celland DevelopmentalBiology p.le Aldo Moro 5 00185 Rome Italy Fax 39 064 991 2351 Tel 39 064 991 2215 E-mail michele.bianchi@uniroma1.it Received 10 December 2007 accepted 30 January 2008 Biological functions governed by the circadian clock are the evident result of the entrainment operated by the earth s day and night cycle on living organisms. However the circadian clock is not unique and cells and organisms possess many other cyclic activities. These activities are difficult to observe if carried out by single cells and the cells are not coordinated but if they can be detected cell-to-cell cross-talk and synchronization among cells must exist. Some of these cycles are metabolic and cell synchronization is due to small molecules acting as metabolic messengers. We propose a short survey of cellular cycles paying special attention to metabolic cycles and cellular cross-talking particularly when the synchronization of metabolism or more generally cellular functions are concerned. Questions arising from the observation of phenomena based on cell communication and from basic cellular cycles are also proposed. doi 10.1111 j.1742-4658.2008.06397.x By cosmic rule as day yields night so winter summer war peace plenty famine. All things change. the harmonious structure of the world depends upon opposite tensions. Heraclitus 500 Bc In the modern age life scientists subscribe to the ergodic cell hypothesis Fig. 1 they use homogenized tissues or cultured cells analyze extracts and draw conclusions about a hypothetical representative cell on the basis that all cells are on average identical over short time and space .
