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

Abstract

Measuring 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.

Two light sensors decode moonlight versus sunlight to adjust a plastic circadian/circalunidian clock to moon phase

“…1 A ) during the night ( 3 ). Whereas it is well established that this swarming is synchronized to specific nights of the month by a circalunar oscillator ( 1 , 4 , 5 ), we reasoned that it should further increase reproductive success if worms synchronized the onset of swarming behavior also to specific hours during those nights. In fact, such an interconnection of different timing systems is well established for polychaete relatives like the palolo worms ( 6 ) and fireworms ( Odontosyllis ) ( 7 ).…”

“…( B ) Swarming onset of individual, separated worms across different days of an artificial lunar month, where worms receive eight nights of continuous nocturnal light (FM) every month in addition to a 16:8 h LD cycle (for details, see refs. 1 , 2 ). Red arrow indicates from which day of the circalunar cycle onward worms were used for all subsequent experiments (except Fig.…”

“…Based on expression changes, a distant homolog (Cry2) in the coral Acropora has been speculated to mediate moonlight sensation ( 13 ). In a separate study, we uncovered that Pdu- L-Cry has the biochemical and cellular properties to discriminate between sunlight and moonlight and is required to correctly detect the FM phase for monthly oscillator entrainment ( 1 ).…”

“…To assess if Platynereis L-Cry is also relevant for the light input into an oscillator with the period length of ∼24 h, the PCC clock, we analyzed a Platynereis l-cry loss-of-function strain generated by Transcription activator-like effector nucleases (TALEN) technology (for details on mutants, see ref. 1 ). When exposed to constant darkness, l-cry −/− individuals still exhibited rhythmic initiation of swarming onset, with a period length (24.6 ± 0.3 h) indistinguishable from wild types ( Fig.…”

“…Alternatively, these findings are compatible with a role of L-Cry in distinguishing moonlight and sunlight, as L-Cry enables the PCC clock to respond differently to the two light conditions and as it also possesses this property in the context of the worm’s monthly oscillator (for monthly oscillator, see ref. 1 ). To discriminate between the two possibilities, we exposed l-cry mutants to a combined naturalistic day/night light regime of 16:8 h, where they were exposed to naturalistic sunlight during the day and naturalistic moonlight during the entire night, mimicking the FM situation (light:moonlight [LM]) ( Fig.…”