Editors' ChoiceCircadian Rhythms

Keeping an Eye on the Master Clock

Science's STKE  11 Feb 2003:
Vol. 2003, Issue 169, pp. tw60-TW60
DOI: 10.1126/stke.2003.169.tw60

Lee at al. have described a circadian pattern of mitogen-activated protein kinase (MAPK) phosphorylation in the suprachiasmatic nucleus (SCN) that depends on input from the eye. The SCN functions as the master pacemaker that drives physiological and behavioral circadian rhythms in mammals. Although SCN clocks are reset by environmental inputs such as light, all SCN rhythms are currently believed to be endogenously generated independent of input from outside the SCN. Lee et al. used an antibody specific for the phosphorylated form of the MAPKs extracellular signal-regulated kinase 1 and 2 (ERK) to immunostain sections of hamster SCN at different circadian times. They observed two rhythmic patterns of ERK phosphorylation for hamsters housed in constant dim light. During the subjective day, a shell-like pattern of phosphorylated ERK (pERK) appeared, whereas during subjective night, pERK was only apparent in a core-like pattern within the caudal SCN. Transplanted SCNs, which restored behavioral and physiological rhythmicity to SCN-lesioned hamsters but did not receive the normal neuronal inputs, showed the shell pattern of pERK rhythm but not the core pattern. Similarly, hamsters and mice whose eyes were removed showed behavioral and physiological circadian rhythms but not the core pERK rhythm. Tract-tracing experiments suggested that the pERK cells in the core region received input from cells in the retina. These data suggest that circadian cycling in at least one region of the SCN depends on input from the retina.

H. S. Lee, J. L. Nelms, M. Nguyen, R. Silver, M. N. Lehman, The eye is necessary for circadian rhythm in the suprachiasmatic nucleus. Nature Neurosci. 6, 111-112 (2003). [Online Journal]