Photoreception and circadian clock system of the chicken pineal gland

Chicken pinealocytes contain three major components of the circadian clock system: a self-sustained oscillator, a photic-input pathway, and rhythmic melatonin production.

• The input-oscillator-output functions of the circadian clock system are maintained even in cultured isolated pineal glands or dissociated pinealocytes.
• The chicken pineal gland is a valuable model for studying the circadian clock system due to its experimental advantages.
• A pineal-specific photoreceptive molecule, pinopsin, has been identified and the endogenous phototransduction pathway in pinealocytes has been characterized.
• Characterization of chick pineal clock genes indicates they likely form a transcription/translation-based autoregulatory feedback loop.
• This feedback loop is similar to the one responsible for circadian rhythmicity in mammalian suprachiasmatic nucleus (SCN).

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