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. 2000 Oct 19;10(20):1291-4.
doi: 10.1016/s0960-9822(00)00758-2.

Multiple signaling pathways elicit circadian gene expression in cultured Rat-1 fibroblasts

A Balsalobre  1 , L Marcacci, U Schibler
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Free article

Multiple signaling pathways elicit circadian gene expression in cultured Rat-1 fibroblasts

A Balsalobre et al. Curr Biol. .
Free article

Abstract

In mammals, all overt circadian rhythms are thought to be coordinated by a central pacemaker residing in the hypothalamic suprachiasmatic nucleus (SCN) [1]. The phase of this pacemaker is entrained by photic cues via the retino-hypothalamic tract. Circadian clocks probably rely on a feedback loop in the expression of certain clock genes (reviewed in [2,3]). Surprisingly, however, such molecular oscillators are not only operative in pacemaker cells, such as SCN neurons, but also in many peripheral tissues and even in cell lines kept in vitro [4-7]. For example, a serum shock can induce circadian gene expression in cultured Rat-1 fibroblasts [5]. This treatment also results in a rapid surge of expression of the clock genes Per1 and Per2, similar to that observed in the SCNs of animals receiving a light pulse [8-10]. Serum induction of Per1 and Per2 transcription does not require ongoing protein synthesis [5] and must therefore be accomplished by direct signaling pathways. Here, we show that cAMP, protein kinase C, glucocorticoid hormones and Ca2+ can all trigger a transient surge of Per1 transcription and elicit rhythmic gene expression in Rat-1 cells. We thus suspect that the SCN pacemaker may exploit multiple chemical cues to synchronize peripheral oscillators in vivo.

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