Circadian oscillation of photopigment transcript levels in the mouse retina

The mammalian retina contains an autonomous circadian oscillator that can s ustain rhythms in outer segment disc shedding and melatonin synthesis even in the absence of cues from the central oscillator in the suprachiasmatic n ucleus (SCN). The present investigation aimed to ascertain whether the stea dy-state levels of rod and cone opsin mRNA exhibited a circadian oscillatio n in the mouse, and if so, to characterise this oscillation with regard to phase. Retinas were collected from mice free-running in constant darkness a t circadian times (CT) 0, 4, 12?,, 16, and 20. RNA was extracted for the pr oduction of Northern blots, which were sequentially hybridised with probes for a-tubulin (control), ultraviolet opsin and rhodopsin. Whereas no signif icant oscillation was detected in the levels of a-tubulin, the levels of bo th ultraviolet opsin and rhodopsin transcripts oscillated with an amplitude of at least 3-fold The highest levels were found at around CT12 (which cor responds to the subjective evening, the time of activity onset in the mouse ). These results show that the levels of rod and cone photopigment mRNA are under circadian control. The significance of the rhythms and their phasing is discussed. These findings have potential clinical implications both wit h regard to nocturnal light treatment of phase asynchrony, and in the timin g of chemo- and radiotherapy. (C) 1999 Elsevier Science B.V. All rights res erved.