Figure 1.

Studying peripheral oscillators in humans [adapted from Ref. (10) with permission]. The master clock in the suprachiasmatic nuclei (SCN) of the hypothalamus maintains phase coherence between peripheral oscillators present in virtually all cells of the body by means of daily synchronizing cues (hormonal signals, neuronal signals, rest/activity and feeding/fasting control, body temperature regulation). Circadian gene expression of different peripheral tissues, such as thyroid gland (68), skeletal muscle myotubes (Laurent Perrin and Charna Dibner, unpublished), pancreatic islets (69), or skin fibroblasts (61, 63), can be monitored in vitro in synchronized cultured cells from patients biopsies or donors samples using bioluminescent circadian reporters (Bmal1-luciferase in this scheme). Circadian properties of these oscillators (phase, period, amplitude, magnitude, resetting) can be analyzed to give subject-specific circadian phenotype information that might be included in diagnostic procedures in the near future.