Signs of the time: environmental input to the circadian clock.
The circadian clock forms one of the most fascinating adaptations to life on earth. Organisms can not only anticipate the day/night cycle but can make use of an internal clock to measure daylength as an indicator of the changing of the seasons. The innate period of the clock is not exactly equal to 24 h, but is reset each day by environmental signals at dawn and dusk, most notably by changes in light and temperature. This ability to re-entrain also ensures that the clock is synchronized with the day/night cycle which in turn is crucial for anticipation of dawn and dusk. Recent advances in the field have identified the photoreceptors involved in resetting the clock in several systems. This has revealed surprising similarities, but also key differences in the circadian systems of plants, fungi, insects, and mammals. One recurring feature emerging from this research is that the photoreceptors themselves are under the control of the clock with transcript abundance being tightly regulated. Furthermore, elements of a feedback pathway whereby the clock modulates the activity of the light input pathway are now being identified.
Devlin
Paul F
PF
Division of life Sciences, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 8WA, UK. paul.delvin@kcl.ac.uk
D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins / Q000502:physiology; D005658:Fungi / Q000502:physiology / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D007313:Insecta / Q000502:physiology / Q000528:radiation effects; D008027:Light; D010786:Photoreceptor Cells / Q000502:physiology; D017956:Photoreceptor Cells, Invertebrate; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology; D020283:Photoreceptors, Microbial / Q000502:physiology; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D010834:Phytochrome / Q000502:physiology; D051939:Phytochrome B; D063245:Plant Development; D010944:Plants / Q000235:genetics / Q000528:radiation effects*; D043562:Receptors, G-Protein-Coupled; D013696:Temperature; D014157:Transcription Factors
D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; D020283:Photoreceptors, Microbial; D045322:Photosynthetic Reaction Center Complex Proteins; D043562:Receptors, G-Protein-Coupled; D014157:Transcription Factors; C119828:cry protein, Drosophila; D010834:Phytochrome; D051939:Phytochrome B