Control of a key enzyme in the fish pineal gland involves protein breakdown

Pike exhibit a physiological day/night rhythm in pineal AANAT2 protein levels, which decreases with midnight light exposure.

• Individual photoreceptor cells in the pineal organ and retina of fish have complete systems for generating melatonin rhythms.
• In pike and seabream, these systems include a light detector, a circadian clock, and machinery for melatonin synthesis.
• The nocturnal increase in melatonin is partly due to the activity of the enzyme AANAT, which is inhibited by light.
• AANAT1 is found in the retina, while AANAT2 is located in the pineal organ, with specific expression patterns in different fish.
• Blocking proteasomal degradation can prevent the light-induced decrease in AANAT2 activity and protein levels.
• A cAMP-dependent pathway may play a role in protecting AANAT2 protein from degradation.

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