Chick pineal clock regulates serotonin N -acetyltransferase mRNA rhythm in culture

Jan 7, 1997Proceedings of the National Academy of Sciences of the United States of America

Pineal gland’s internal clock controls daily rhythm of serotonin-processing gene in chicken cells

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Abstract

Melatonin production in the chick pineal gland is high at night and low during the day.

AA-NAT mRNA levels in cultured chick pineal cells show a rhythm that parallels changes in AA-NAT activity.
Elevating cAMP with forskolin increases AA-NAT activity without significantly altering AA-NAT mRNA levels.
Lowering cAMP with norepinephrine decreases AA-NAT activity without markedly reducing mRNA levels.
Clock-controlled changes in AA-NAT activity primarily occur through variations in mRNA levels.
The nocturnal increase in AA-NAT mRNA requires gene expression but does not necessitate new protein synthesis.

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Melatonin production in the chick pineal gland is high at night and low during the day. This rhythm reflects circadian changes in the activity of serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase, AA-NAT; EC 2.3.1.87), the penultimate enzyme in melatonin synthesis. In contrast to the external regulation of pineal rhythms in mammals by the suprachiasmatic nucleus, rhythmic changes in AA-NAT activity in cultured chick pineal cells are controlled by an oscillator located in the pineal cells themselves. Here we present evidence that the chick pineal clock generates a rhythm in the abundance of AA-NAT mRNA in cultured cells that parallels the rhythm in AA-NAT activity. In contrast, elevating cAMP by forskolin treatment markedly increases AA-NAT activity without producing strong changes in AA-NAT mRNA levels, and lowering cAMP by norepinephrine treatment decreases enzyme activity without markedly decreasing mRNA. These results suggest that clock-controlled changes in AA-NAT activity occur primarily through changes at the mRNA level, whereas cAMP-controlled changes occur primarily through changes at the protein level. Related studies indicate that the clock-dependent nocturnal increase in AA-NAT mRNA requires gene expression but not de novo protein synthesis, and that AA-NAT mRNA levels are suppressed at all times of the day by a rapidly turning over protein. Further analysis of the regulation of chick pineal AA-NAT mRNA is likely to enhance our understanding of the molecular basis of vertebrate circadian rhythms.

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Chick pineal clock regulates serotonin N -acetyltransferase mRNA rhythm in culture

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