However, many organisms also exhibit rhythms of longer and shorter period lengths ( Aschoff, 1981 Naylor, 2010). The feedback loops continue to run under constant conditions and are coordinated with the animal’s environment by entrainment ( Cold Spring Harbor Symposia on Quantitative Biology, 2007 Roenneberg and Merrow, 2005). These genes are partially shared between insect and mammalian models, arguing for a common origin of animal circadian clocks. One of the critical mechanisms driving animal circadian clocks are transcriptional/translational feedback loops formed by a set of regulatory genes. Efforts to study the underlying molecular mechanisms have focused almost exclusively on circadian clocks (i.e., clocks anticipating daily cycles). Most, if not all, organisms feed periodic changes in light conditions into molecular clockworks that allow them to anticipate rhythmic changes in their environment and to synchronize their behavior and physiology ( Cold Spring Harbor Symposia on Quantitative Biology, 2007 Roenneberg and Merrow, 2005). We conclude that a second endogenous noncircadian clock can influence circadian clock function. Furthermore, the circalunar clock changes the period and power of circadian behavior, although the period length of the daily transcriptional oscillations remains unaltered. Both circadian and circalunar clocks converge on the regulation of transcript levels. This monthly clock regulates maturation and persists even when circadian clock oscillations are disrupted by the inhibition of casein kinase 1δ/ε. The worm’s forebrain also harbors a circalunar clock entrained by nocturnal light. The RNAs of likely core circadian oscillator genes localize to a distinct nucleus of the worm’s forebrain.
We establish that the marine worm Platynereis dumerilii possesses endogenous circadian and circalunar (monthly) clocks and characterize their interactions. Although the interaction of the daily (circadian) clock with environmental stimuli, such as light, is well documented, its relationship to endogenous clocks with other periods is little understood.
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