Expression of Melatonin-Related Enzymes in the Eye and Skin of Three-Spined Stickleback Fish

Melatonin production in the three-spined stickleback's eyeball and skin may be regulated by the expression of four genes at different times of day.

• mRNA for four genes associated with melatonin synthesis was found in the eyeball, while two were detected in the skin.
• Two transcripts each of AANAT and ASMT genes were present in the eyeball at both noon and midnight, indicating potential additional metabolic roles.
• Day/night variations in melatonin levels did not correlate with gene expression or AANAT activity, suggesting complex regulatory mechanisms.
• High efficacy of N-acetylserotonin synthesis in the eyeball at low substrate levels implies a role beyond just melatonin production.
• AANAT isozyme activity inhibition by its product could be a mechanism for serotonin regulation in the retina.
• Local melatonin synthesis is supported by the presence of AANAT and ASMT gene transcripts and AANAT activity in the skin at both times.

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