Peripheral clocks: keeping up with the master clock

Circadian clocks influence most aspects of physiology and behavior, so perhaps it is not surprising that circadian oscillators exist in nearly all mammalian cells. These cells remain synchronized to the outside world in hierarchical fashion, with a "master clock" tissue in the suprachiasmatic nucleus of the hypothalamus receiving light input from the retina and then conveying timing information to "slave" clocks in peripheral tissues. Recent research has highlighted both the similarities and differences between central and peripheral clocks and provided new insight into their communication. Above all, however, this parallelism of clockwork has provided a unique opportunity to study at the cellular level a regulatory mechanism that affects complex behaviors.