Signaling to the Mammalian Circadian Clocks: In Pursuit of the Primary Mammalian Circadian Photoreceptor

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Science's STKE  06 Nov 2001:
Vol. 2001, Issue 107, pp. re16
DOI: 10.1126/stke.2001.107.re16

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The mammalian circadian system contains central and peripheral molecular clocks that control daily changes in physiology and behavior. The central or master clock is located in a region of the brain called the hypothalamic suprachiasmatic nucleus (SCN). Circadian clocks maintain cycles of about 24 hours. The phase of the master clock is primarily set by environmental light cycles, whereas peripheral clocks are thought to be set primarily by light-independent (nonphotic) signals originating from the SCN. Photic and nonphotic signals alter the phase of a molecular clock by stimulating gene activation that fine-tunes the interlocking positive and negative regulatory feedback loops that make up a circadian oscillator.