A Cryptochrome adopts distinct moon- and sunlight states and functions as moonlight interpreter in monthly oscillator entrainment

Abstract

AbstractMeasuring time by the moon’s monthly cycles is a wide-spread phenomenon and crucial for successful reproduction in countless marine organisms. In several species, such as the mass-spawning bristle worm Platynereis dumerilii, an endogenous monthly oscillator synchronizes reproduction to specific days. Classical work showed that this oscillator is set by full moon. But how do organisms recognize this specific moon phase?We uncover L-Cry’s involvement: photoreduction and recovery kinetics of its co-factor FAD differ strongly when purified L-Cry is exposed to naturalistic moonlight, naturalistic sunlight, or their different successions. L-Cry’s sun-versus moonlight states correlate with distinct sub-cellular localizations, indicating differential signalling. These properties enable a discrimination between sun- and moonlight, as well as moonlight duration as a moon phase indicator.Consistently, l-cry mutants re-entrain their circalunar phase less well than wild-type to naturalistic moonlight. But under artificially strong nocturnal light, l-cry mutants re-entrain faster than wildtype, suggesting that L-Cry at least partly blocks “wrong” light from impacting on this oscillator. Our work provides a new level of functional understanding of moon-regulated biological processes.