Editors' ChoiceCircadian Rhythms

Seeing in the Dark

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Science's STKE  30 Jan 2001:
Vol. 2001, Issue 67, pp. tw6
DOI: 10.1126/stke.2001.67.tw6

Many aspects of visual system physiology are regulated by circadian oscillators. Ko et al. report that chick photoreceptor cells in culture or in ovo can be entrained by light/dark cycles and that they exhibit a persistent circadian alteration in the affinity of the cyclic guanosine monophosphate (cGMP)-gated channels for cGMP. The affinity is higher at night and lower in the day after training with a 12-hour light/12-hour dark schedule. The molecular mechanism for the circadian change in affinity was investigated with pharmacological inhibitors and showed that the circadian rhythm was the result of antiphasic activities of extracellular signal-regulated protein kinase (ERK) and calcium/calmodulin kinase II (CaMKII). Inhibition of ERK activity blocked the increase in affinity seen during the night. The decreased affinity for cGMP was the result of rhythmic calcium/calmodulin kinase II (CaMKII) activity (that peaks in the day). Furthermore, inhibition of ERK disrupted both the dark phase increase in affinity and the rhythmic CaCMKII activity (and subsequent decrease in cGMP affinity), suggesting that ERK may be conveying information from the oscillator to CaMKII.

G. Y.-P. Ko, M. L. Ko, S. E. Dryer, Circadian regulation of cGMP-gated cation channels of chick retinal cones: Erk MAP kinase and Ca2+/calmodulin-dependent protein kinase II. Neuron 29, 255-266 (2001). [Online Journal]

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