The avian pineal gland is an independent molecular oscillator that receives external light information that regulates the synthesis and secretion of melatonin. Arylalkylamine N-acetyltransferase plays an important role in the pineal gland by controlling the rhythmic production of melatonin. Previous study showed that monochromatic light influences the secretion of melatonin, which is regulated by the molecular circadian clock genes in chick pineal gland. This study was designed to investigate the effect of monochromatic light on the circadian rhythm of levels of c, clock protein (CLOCK and BMAL1), c, and opsins (c; c; c) in chick pineal gland. A total of 240 post-hatching day (P) 0 broiler chickens were reared under white (WL), red (RL), green (GL), and blue light (BL) with light (L)-dark (D) cycle of 12L:12D for 14 d. The results show significant circadian rhythms in the expression of c, CLOCK, BMAL1, c, c, c, and c, but not for cunder RL. Compared with WL, GL increased the level ofmRNA, while RL decreased it. Meanwhile, CLOCK and BMAL1 proteins were expressed at high levels in GL. Furthermore, the peak of the 24 h pattern ofmRNA in GL was earlier than that of in WL, RL, and BL. These results demonstrated that monochromatic light affects the daily expression ofin the chick pineal gland via the biological clock. GL activates the transcription of, while RL suppresses the transcription of. Meanwhile, GL appears to induce the peak ofmRNA in advance to affect the transmission of light. Thus, monochromatic light regulatesin the chick pineal gland by affecting the levels of clock regulators via entraining the expression of pineal gland opsins. Aanat Creb Opnp, Pinopsin Opn4-1, Melanopsin-1Opn4-2, Melanopsin-2Aanat Creb Opnp Opn4-1Opn4-2Opnp cAanat cOpnp cAanat cAanat cAanat cOpnp cAanat
