Transcriptional regulation of hydroxyindole O -methyltransferase in the chicken pineal gland: day/night changes and long-term effects of light and darkness
Coimbra, Joao Carlos; Pinto, Iraja Damiani; Wurdig, Norma Luiza; Do Carmo, Dermeval Aparecido
Biochemical Journal 290(3): 661-664
ISSN/ISBN: 0264-6021 DOI: 10.1042/bj2900661
The indolic hormone melatonin is produced by the pineal gland according to a daily rhythm. The terminal step of melatonin synthesis is catalysed by hydroxyindole O-methyltransferase (HIOMT, EC 184.108.40.206). Adaptation to constant light or darkness modifies HIOMT activity and concentration. Using a cDNA probe encoding HIOMT, we investigated the effect of environmental lighting on HIOMT gene expression in the chicken pineal gland. HIOMT mRNA levels increased by 100% in constant light as compared with constant darkness. In addition, the present study disclosed the existence of a day/night rhythm of HIOMT gene transcription, with 3-fold higher mRNA levels at midday than at midnight. This transcriptional rhythm was not accompanied by day/night changes in HIOMT concentration, probably due to a slow turnover of this protein. Unexpected darkness did not prevent the daytime rise in HIOMT mRNA levels, whereas unexpected light prevented the night-time fall in HIOMT mRNA levels. Together, the data would suggest that the day/night rhythm of HIOMT gene transcription in the chicken pineal gland involves both a response to light and the activity of a biological oscillator.