Light‐Dependent Expression of Pinopsin Gene in Chicken Pineal Gland

Abstract

The phase of a circadian clock in the chicken pineal gland is reset by an environmental light signal, which is captured by the pineal photoreceptive molecule(s). Here we show that the mRNA level of pinopsin, a predominant photoreceptive molecule in the pineal gland, undergoes a diurnal fluctuation in chickens maintained on a light/dark cycle. The mRNA levels in the light were approximately six times higher than those in the dark. This fluctuation was not observed in constant darkness, where the mRNA levels remained low. Subsequent light exposure of chickens increased the amount of pinopsin mRNA regardless of the circadian time. Clearly, the expression of pinopsin gene is controlled by a light signal, independent of the circadian clock. In vitro experiments using cultured pineal glands isolated from the visual system also revealed the light‐dependent increase in pinopsin mRNA level, indicating that the pineal photoreceptive molecule(s) is responsible for the induction. These results demonstrate the presence of a feedback loop through which the light signal captured by pinopsin stimulates the transcription of its own gene in the chicken pineal gland. In contrast, pinopsin protein remained at an almost constant level in chickens maintained under the same light/dark cycles. The protein level, however, decreased to ∼50% of the light/dark level under constant darkness and subsequently increased upon exposure to light after the dark period. It is suggested that, under the light/dark cycles, the pinopsin protein level is kept constant by the light‐dependent synthesis, which would compensate for a possible degradation of pinopsin in the daytime.

Single-cell recordings from chick pineal glands in vitro reveal ultradian and circadian oscillations

“…The following observations are in agreement with the assumption of circadian rhythmicity: (1) the phases of low and high activity do not precisely follow the light/dark phases, (2) the calculated periods are not 24 h but longer (26.25 h), (3) the rhythm persists under constant lighting conditions and (4) the rhythm can be phase-advanced by exposing the donors to a phase-advanced lighting cycle. Abundant evidence is available that the chick pineal gland is sensitive to light in vitro [1, 2,6,25]. Since the rhythms of the cells from glands exposed to LD 12:12 exhibit periods longer than 24 h, the time cues provided by the LD cycle are not apparently sufficient to set the Figure 4.…”

Avian central clocking system

“…W przypadku pinopsyny w szyszynce kury rytmiczne dobowe wahania poziomu jej mRNA były obserwowane tylko w trakcie wystę-powania następujących po sobie faz jasnej i ciemnej. W odróżnieniu od mRNA, zawartość białka pinopsyny była stała i nie podlegała wpływowi światła i oscylatora (83). Pinopsyna hamuje bezpośrednio wydzielanie melatoniny poprzez oddziaływanie na podjednostki α białka G t hamujące aktywność cyklazy adenylanowej i zależnych od niej enzymów szlaku biosyntezy melatoniny (47,48,61,67,68,70,71).…”

Novel functions for Period 3 and Exo-rhodopsin in rhythmic transcription and melatonin biosynthesis within the zebrafish pineal organ

“…Many other opsin genes are also expressed with a strong daily rhythm [6][7][8]13,17,[23][24][25]29,31,33,35,42,49,50,55,59]. However, the function of this rhythmic expression is not well understood.…”