title: Transcripts encoding two melatonin synthesis enzymes in the teleost pineal organ: circadian regulation in pike and zebrafish, but not in trout.
abstract: In this report the photosensitive teleost pineal organ was studied in three teleosts, in which melatonin production is known to exhibit a daily rhythm with higher levels at night; in pike and zebrafish this increase is driven by a pineal clock, whereas in trout it occurs exclusively in response to darkness. Here we investigated the regulation of messenger RNA (mRNA) encoding serotonin N-acetyltransferase (AA-NAT), the penultimate enzyme in melatonin synthesis, which is thought to be primarily responsible for changes in melatonin production. AA-NAT mRNA was found in the pineal organ of all three species and in the zebrafish retina. A rhythm in AA-NAT mRNA occurs in vivo in the pike pineal organ in a light/dark (L/D) lighting environment, in constant lighting (L/L), or in constant darkness (D/D) and in vitro in the zebrafish pineal organ in L/D and L/L, indicating that these transcripts are regulated by a circadian clock. In contrast, trout pineal AA-NAT mRNA levels are stable in vivo and in vitro in L/D, L/L, and D/D. Analysis of mRNA encoding the first enzyme in melatonin synthesis, tryptophan hydroxylase, reveals that the in vivo abundance of this transcript changes on a circadian basis in pike, but not in trout. A parsimonious hypothesis to explain the absence of circadian rhythms in both AA-NAT and tryptophan hydroxylase mRNAs in the trout pineal is that one circadian system regulates the expression of both genes and that this system has been disrupted by a single mutation in this species.
authors.affiliation: Département des Neurosciences, CNRS-UMR 6558, Faculté des Sciences, Poitiers, France.
authors.forename: V
authors.initials: V
authors.lastname: Bégay
authors.forename: J
authors.initials: J
authors.lastname: Falcón
authors.forename: G M
authors.initials: GM
authors.lastname: Cahill
authors.forename: D C
authors.initials: DC
authors.lastname: Klein
authors.forename: S L
authors.initials: SL
authors.lastname: Coon
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000235:genetics*; D002940:Circadian Rhythm; D017859:Esocidae / Q000378:metabolism; D005260:Female; D005399:Fishes / Q000378:metabolism*; D005786:Gene Expression Regulation; D008297:Male; D008550:Melatonin / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D009924:Organ Culture Techniques; D010870:Pineal Gland / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis*; D014337:Trout / Q000378:metabolism; D015027:Zebrafish / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D001191:Arylamine N-Acetyltransferase; D008550:Melatonin