RESUMEN
The circadian rhythms in melatonin production in the chicken pineal gland and retina reflect changes in the activity of serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase; AA-NAT; EC 2.3.1.87). Here we determined that the chicken AA-NAT mRNA is detectable in follicular pineal cells and retinal photoreceptors and that it exhibits a circadian rhythm, with peak levels at night. AA-NAT mRNA was not detected in other tissues. The AA-NAT mRNA rhythm in the pineal gland and retina persists in constant darkness (DD) and constant lighting (LL). The amplitude of the pineal mRNA rhythm is not decreased in LL. Light appears to influence the phase of the clock driving the rhythm in pineal AA-NAT mRNA in two ways: The peak is delayed by approximately 6 h in LL, and it is advanced by > 4 h by a 6-h light pulse late in subjective night in DD. Nocturnal AA-NAT mRNA levels do not change during a 20-min exposure to light, whereas this treatment dramatically decreases AA-NAT activity. These observations suggest that the rhythmic changes in chicken pineal AA-NAT activity reflect, at least in part, clock-generated changes in mRNA levels. In contrast, changes in mRNA content are not involved in the rapid light-induced decrease in AA-NAT activity.
Asunto(s)
Arilamina N-Acetiltransferasa/genética , Pollos/metabolismo , Ritmo Circadiano , Luz , Melatonina/biosíntesis , ARN Mensajero/metabolismo , Secuencia de Aminoácidos , Animales , Arilamina N-Acetiltransferasa/metabolismo , Clonación Molecular , ADN Complementario/genética , Datos de Secuencia Molecular , Glándula Pineal/metabolismo , Retina/metabolismoRESUMEN
In vertebrates, the circadian rhythm in the activity of serotonin N-acetyltransferase [arylalkylamine N-acetyltransferase (AA-NAT); EC 2.3.1.87] drives the daily rhythm in circulating melatonin. We have discovered that expression of the AA-NAT gene in the rat pineal gland is essentially turned off during the day and turned on at night, resulting in a more than 150-fold rhythm. Expression is regulated by a photoneural system that acts through an adrenergic-cAMP mechanism in pinealocytes, probably involving cAMP response element-binding protein phosphorylation. Turning off AA-NAT expression appears to involve de novo synthesis of a protein that attenuates transcription. A approximately 10-fold night/day rhythm in AA-NAT messenger RNA occurs in the retina, and AA-NAT messenger RNA is also detected at low levels in the brain.