Molecular cloning of the arylalkylamine-N-acetyltransferase and daily variations of its mRNA expression in the Syrian hamster pineal gland

Jul 17, 1999Brain research. Molecular brain research

Cloning a key enzyme and its daily gene activity in the Syrian hamster's pineal gland

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Abstract

A PCR-generated clone of 1045 bp encoding the AA-NAT has been isolated and sequenced in the Syrian hamster.

AA-NAT is responsible for converting serotonin to N-acetylserotonin, a key step in melatonin production.
Strong daily fluctuations in AA-NAT mRNA expression were observed, with levels undetectable in the latter half of the light period.
A dramatic increase in AA-NAT mRNA expression occurs at night, peaking 6-7 hours after lights off.
The timing of AA-NAT mRNA transcription may influence the delay in melatonin synthesis and pineal gland responsiveness to darkness.

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The arylalkylamine-N-acetyltransferase (AA-NAT) expressed in the vertebrate pineal gland catalyzes the N-acetylation of the serotonin into N-acetylserotonin and is considered to be the rate limiting enzyme of the pineal melatonin synthesis. Indeed, dramatic changes in its activity throughout the 24-h period drive the large day/night variations in plasma melatonin concentrations. Recently, AA-NAT was cloned in the rat pineal. In this species, AA-NAT mRNA variations were demonstrated to be responsible of the well known AA-NAT activity and plasma melatonin circadian fluctuations. In the Syrian hamster, the pineal melatonin secretion pattern is characterized by a late-night short-duration peak of melatonin synthesis. We investigated whether this typical pattern could be due to a late-night delayed pineal AA-NAT mRNA expression. The first part of our study was dedicated to the molecular cloning of a Syrian hamster AA-NAT cDNA. A PCR-generated clone of 1045 bp encoding the AA-NAT has been isolated and sequenced. In situ hybridization using an AA-NAT cRNA probe revealed that the AA-NAT mRNA expression undergoes strong daily fluctuations in the Syrian hamster pineal, with undetectable level in the second half of the light period and a dramatic increase at night. After lights off, the AA-NAT mRNA expression requires 6-7 h to reach its maximum expression. This result thus suggests that the transcription of the AA-NAT mRNA in the Syrian pineal gland determines the lag period in pineal responsiveness and melatonin synthesis to darkness.

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Molecular cloning of the arylalkylamine-N-acetyltransferase and daily variations of its mRNA expression in the Syrian hamster pineal gland

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