In most organisms including humans, physiology and behavior are coordinated by an internal molecular clock. These rhythms are synchronized with the 24h solar day and termed as circadian rhythms. At a molecular level, the circadian clock is governed by the interplay between several proteins such as CLOCK, CYCLE, PERIOD and CRY and is regulated by transcription-translation feedback loop. These regulatory proteins are partially conserved between several insect and mammalian systems indicating a possible evolutionary function. Many organisms align their behavior not only to the changes of the sun but also to the cycles of the moon (monthly timing). The bristle worm Platynereis was among the first organisms for which the entrainment to a lunar cycle was shown to only depend on nocturnal light stimuli. Thus, Platynereis dumerilli has a circalunar (monthly) clock in addition to the circadian (daily) clock. The locomotor activity of the worm is under the control of the circadian clock. The circalunar clock regulates the maturation of Platynereis adjusting its reproduction to the lunar phase. Platynereis is a suitable model to study the interplay between circadian and circalunar clock components and the influence of this on the behavior of the organism. It has been established that the circalunar clock of the worm affects the circadian clock at several levels and the circalunar clock persists even when the circadian clock is disrupted.
Cryptochromes are well studied components of the circadian clock which have the potential to function as light receptors in some species. This study focuses on the characterization of the cryptochromes from Platynereis dumerilli to provide insights to their role in circadian and/or circalunar clocks. Platynereis dumerilli possess 3 different kinds of cryptochromes, one each similar to the drosophila (L-CRY), mammalian repressor (TR-CRY) and plant (P-CRY) cryptochromes. Studies with S2 cells also established that TR-CRY functions as a transcriptional repressor cryptochrome as in mammals. However, the role of L-CRY and P-CRY remain to be elucidated.
In this thesis, characterization of L-CRY and P-CRY has been carried out with purified proteins. Here, we have purified the Platynereis L-CRY and P-CRY proteins and analyzed them by UV/VIS- and fluorescence spectroscopy, high performance liquid chromatography (HPLC) and static light scattering (MALS/SLS) to determine the oligomeric state, their cofactors bound and to propose their photoreaction mechanisms. Our analyses suggest possible roles of Platynereis L-CRY and P-CRY as flavin-dependent photoreceptors. SAXS and electron microscopy analysis provided structural information regarding L-CRY with the detection of a novel dimer interface. To gain further insights into the functional role of these cryptochromes, a mass spectrometry-based approach helped to determine potential interacting partners. The next level of understanding will be to discern how these different cryptochromes and their interactors are molecularly connected and to what extent underlying molecular clocks share same components.197 page
