Chick pineal clock regulates serotonin N-acetyltransferase mRNA rhythm in culture
Chick pineal clock regulates serotonin N-acetyltransferase mRNA rhythm in culture
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DOI：
10.1073/pnas.94.1.304
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发表时间：
1997-01-07
影响因子：
11.1
通讯作者：
Zatz, M
中科院分区：
文献类型：
--
作者：
Bernard, M;Klein, DC;Zatz, M
鸡松果体中褪黑激素的产生在夜间高而在白天低。这种节律反映了5-羟色胺N-乙酰基转移酶（芳基烷基胺N-乙酰基转移酶，AA-NAT; EC 2.3.1.87）活性的昼夜变化，5-羟色胺N-乙酰基转移酶是褪黑激素合成中的倒数第二种酶。相反，在哺乳动物的松果体节律的外部调节视交叉上核，在培养的鸡松果体细胞中的AA-NAT活性的节奏变化是由位于松果体细胞本身的振荡器控制。在这里，我们提出的证据表明，鸡松果体时钟产生的AA-NAT mRNA在培养的细胞中，平行于AA-NAT活性的节奏的丰度的节奏。相反，毛喉素处理提高cAMP显著增加AA-NAT活性而不产生AA-NAT mRNA水平的强烈变化，去甲肾上腺素处理降低cAMP降低酶活性而不显著降低mRNA。这些结果表明，AA-NAT活性的时钟控制的变化主要通过mRNA水平的变化发生，而cAMP控制的变化主要通过蛋白质水平的变化发生。相关研究表明，AA-NAT mRNA的时钟依赖性夜间增加需要基因表达，而不是从头蛋白质合成，并且AA-NAT mRNA水平在一天中的所有时间都受到快速翻转蛋白质的抑制。对鸡松果体AA-NAT mRNA调控的进一步分析可能会增强我们对脊椎动物昼夜节律的分子基础的理解。
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 hy 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.