Synchronized diurnal and circadian expressions of four subtypes of melatonin receptor genes in the diencephalon of a puffer fish with lunar-related spawning cycles

Four melatonin receptor subtype genes exhibit distinct expression patterns in the grass puffer's brain and peripheral tissues.

• Mel(1a) 1.4, Mel(1a) 1.7, and Mel(1b) mRNAs are found in various brain regions, retina, pituitary, and peripheral tissues, while Mel(1c) mRNA is primarily in the nervous tissues and pituitary.
• All melatonin receptor subtype genes display diurnal expression with peaks occurring during nighttime.
• Under constant darkness, expressions of Mel(1a) 1.7, Mel(1b), and Mel(1c) genes in the retina decrease but maintain circadian variations.
• In the diencephalon, synchronized peaks of expression for all four receptor subtypes occur at circadian time 18.
• Circadian expression profiles vary among receptor subtypes in the optic tectum.
• Melatonin receptor gene expression appears to be influenced by both the circadian clock and light, with tissue-specific responses.

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