Contribution of the eye and of < i > opn4xa < /i > function to circadian photoentrainment in the diurnal zebrafish

by Clair Chaigne, Dora Sap ède, Xavier Cousin, Laurent Sanchou, Patrick Blader, Elise Cau The eye is instrumental for controlling circadian rhythms in mice and human. Here, we address the conservation of this function in the zebrafish, a diurnal vertebrate. Usinglakritz (lak) mutant larvae, which lack retinal ganglion cells (RGCs), we show that while a functional eye contributes to masking, it is largely dispensable for the establishment of circadian rhythms of locomotor activity. Furthermore, the eye is dispensable for the induction of a phase delay following a pulse of white light at CT 16 but contributes to the induction of a phase advance upon a pulse of white light at CT21. Melanopsin photopigments are important mediators of photoentrainment, as shown in nocturnal mammals. One of the zebrafish melanopsin genes,opn4xa, is expressed in RGCs but also in photosensitive projection neurons in the pineal gland. Pinealopn4xa+ projection neurons function in a LIGHT ON manner in contrast to other projection neurons which function in a LIGHT OFF mode. We generated anopn4xa mutant in which the pineal LIGHT ON response is impaired. This mutation has no effect on masking and circadian rhythms of locomotor activity, or for the induction of phase shifts, but slightly modifies period length when larvae are subjected to constant light. Finally, analysis ofopn4xa;lak double mutant larvae did not reveal redundancy between the function of the eye andopn4xa in the pineal for the control of ...
Source: PLoS Genetics - Category: Genetics & Stem Cells Authors: Source Type: research