Nature Reviews Genetics 6, 544-556 (July 2005) | doi:10.1038/nrg1633

Circadian rhythms from multiple oscillators: lessons from diverse organisms

Deborah Bell-Pedersen1, Vincent M. Cassone1, David J. Earnest1,2, Susan S. Golden1, Paul E. Hardin3, Terry L. Thomas1  About the authors & Mark J. Zoran1


The organization of biological activities into daily cycles is universal in organisms as diverse as cyanobacteria, fungi, algae, plants, flies, birds and man. Comparisons of circadian clocks in unicellular and multicellular organisms using molecular genetics and genomics have provided new insights into the mechanisms and complexity of clock systems. Whereas unicellular organisms require stand-alone clocks that can generate 24-hour rhythms for diverse processes, organisms with differentiated tissues can partition clock function to generate and coordinate different rhythms. In both cases, the temporal coordination of a multi-oscillator system is essential for producing robust circadian rhythms of gene expression and biological activity.

Author affiliations

  1. Center for Research on Biological Clocks, Department of Biology, Texas A&M University, College Station, Texas 77843-3258, USA.
  2. Department of Human Anatomy and Medical Neurobiology, Texas A&M University, System Health Science Center, College Station, Texas 77843-1114, USA.
  3. Department of Biology and Biochemistry, University of Houston, 4800 Calhoun Road, Houston, Texas 77204-5001, USA.

Correspondence to: Deborah Bell-Pedersen1 Email:


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