General and comparative endocrinologyApr 15, 2004

Changes in melatonin-making and sensing genes in the eye and brain of chum salmon before and after hatching

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Updated Mar 28, 2026

Abstract

Daily rhythmicity in AANAT mRNA levels and melatonin concentrations was observed in the eye and brain of chum salmon throughout development.

AANAT(1) and AANAT(2) mRNA levels, along with Mel(1a) and Mel(1b) receptor transcripts, show developmental increases during embryonic and post-embryonic stages.
Ocular and brain melatonin levels were measured, revealing parallel changes with AANAT mRNA levels.
The findings suggest that increased nocturnal melatonin levels may result from enhanced transcription of AANAT genes.
High expression of AANAT and Mel-R mRNAs in specific brain regions points to potential roles in visual processing and neuroendocrine functions.
These roles could be linked to the migratory behavior of chum salmon.

Simplified

Melatonin and arylalkylamine N-acetyltransferase (AANAT), the rate-limiting enzyme in melatonin synthesis, have taken on special importance in vertebrate circadian biology. Recent identification of genes encoding two AANAT (AANAT(1) and AANAT(2)) and two subtypes of melatonin receptor (Mel-R; Mel(1a) and Mel(1b)) in several fish species has led to rapid advances in characterizing the physiological roles of melatonin. In the present study, partial cDNAs encoding these four genes were cloned from the eye and brain of chum salmon (Oncorhynchus keta). Based on the nucleotide sequences, we developed highly sensitive real-time PCR systems for these four mRNAs. The development of daily rhythmicity in AANAT(1), AANAT(2), Mel(1a), and Mel(1b) transcript levels was examined in the eye and brain of chum salmon during embryonic and post-embryonic stages (from day -9 to day +180). In a parallel experiment, ocular and brain melatonin levels were measured by radioimmunoassay. Parallelism in developmental changes and in circadian rhythms of AANAT mRNAs and melatonin levels in the eye and the brain supports a hypothesis that the developmental increases of nocturnal melatonin levels results partly from the elevated transcription of AANAT genes. Moreover, abundant expression of AANAT and Mel-R mRNAs in the optic tectum, thalamus, hypothalamus, cerebellum, and eye indicates possible roles of melatonin in visual processing and neuroendocrine regulation, through which melatonin might be involved in migratory behavior of chum salmon.

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Changes in melatonin-making and sensing genes in the eye and brain of chum salmon before and after hatching

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