title: Day/night variation of tryptophan hydroxylase and serotonin N-acetyltransferase mRNA levels in the ovine pineal gland and retina.
abstract: In mammals, the photoperiodic information, received by the retina, is transmitted to the pineal gland. In both organs, melatonin is produced and functions as a neurohormone giving temporal information to the organism. A four-step enzymatic pathway, involving in particular the tryptophan hydroxylase (TPOH), the rate-limiting enzyme in serotonin synthesis, and the serotonin N-acetyltransferase (NAT) that converts serotonin to N-acetylserotonin, allows the synthesis of melatonin. Many studies on melatonin synthesis modulation have focused on the enzyme NAT, but the regulation of TPOH is less well understood. We report here a quantitative study, using a reverse transcription polymerase chain reaction (RT-PCR) analysis, of the nycthemeral expression of TPOH and NAT mRNAs in the ovine retina and pineal gland. In both organs, we show a nocturnal increase in mRNA levels of the two enzymes. suggesting a role of transcriptional mechanisms in the regulation of melatonin synthesis. However, the amplitude of the observed increase in TPOH and NAT mRNAs expression can not entirely explain the 7-fold nocturnal increase in the plasma melatonin level. Our results suggest that, in the sheep, post-transcriptional mechanisms might also be involved in the day/night modulation of melatonin production.
authors.affiliation: INSERM U433, Faculté R. Th. Laënnec, Lyon, France. kprivat@lemel.fr
authors.forename: K
authors.initials: K
authors.lastname: Privat
authors.forename: J P
authors.initials: JP
authors.lastname: Ravault
authors.forename: D
authors.initials: D
authors.lastname: Chesneau
authors.forename: M
authors.initials: M
authors.lastname: Fevre-Montange
mesh_terms: D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000235:genetics*; D002940:Circadian Rhythm; D015971:Gene Expression Regulation, Enzymologic; D008027:Light; D008297:Male; D008550:Melatonin / Q000097:blood; D009928:Organ Specificity; D017440:Photoperiod; D010870:Pineal Gland / Q000201:enzymology / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D012160:Retina / Q000201:enzymology / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D012756:Sheep / Q000097:blood / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics; D014365:Tryptophan Hydroxylase / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D014365:Tryptophan Hydroxylase; D001191:Arylamine N-Acetyltransferase; D008550:Melatonin