Carter D A
Institute of Molecular and Cell Biology, National University of Singapore, Kent Ridge Crescent.
Neuroscience. 1994 Oct;62(4):1267-78. doi: 10.1016/0306-4522(94)90358-1.
The daily cycle of phenotypic variation in the mammalian pineal provides a unique model for the investigation of the molecular mechanisms that regulate neurotransmitter synthesis. In the rat, a circadian adrenergic mechanism directs a change in serotonin metabolism that results in the nocturnal production of melatonin. Activity of the activator protein-1 transcriptional regulatory complex, as demonstrated by band-shift assays of rat pineal gland extracts, has now been shown to exhibit a rhythm, in vivo, which is temporally correlated with the rhythm of melatonin synthesis. Thus, nocturnal activator protein-1 activity (23.00 h) is markedly elevated, being 8-fold higher than the level of light-phase activity (P < 0.005). The nocturnal activator protein-1 protein complex is induced through a trans-synaptic, beta-adrenoceptor-linked mechanism and is characterized by the prolonged participation of JunB as demonstrated using antibodies for specific activator protein-1 proteins. Indeed, JunB appears to be a major component of nocturnal changes in activator protein-1 activity, JunD forming an additional, constitutive component which is not affected by the nocturnal adrenergic signal. The alpha 1-adrenoreceptor-linked c-Fos protein, which is coordinately induced with JunB, does not form a stable component of nocturnal activator protein-1 activity. In contrast, parallel experiments showed that c-Fos does form a major component of the hippocampal activator protein-1 complex that is induced in rats following kainic acid treatment. In the pineal, a similar, although not identical, pattern of activator protein-1 activation has also been demonstrated in cultured glands following treatment with norepinephrine. Immunoblotting has demonstrated parallel accumulation of JunB and c-Fos protein in pineal nuclear fractions following stimulation both in vivo and in vitro. The results provide evidence of posttranscriptional selection of neurotransmitter-stimulated activator protein-1 protein complexes, a mechanism which complements the differential induction of fos and jun genes in the pineal, and serves to generate a specific activator protein-1 transcription factor complex. This finding has general implications for the functional interpretation of fos and jun gene induction in neuronal systems. The stable JunB complex demonstrated here may be considered as one component of a timing mechanism which acts to perpetuate synaptic signals and thereby maintain an appropriate period of nocturnal pineal function.
哺乳动物松果体中表型变化的每日周期为研究调节神经递质合成的分子机制提供了一个独特的模型。在大鼠中，一种昼夜节律性肾上腺素能机制指导血清素代谢的变化，导致夜间褪黑素的产生。通过对大鼠松果体提取物进行凝胶迁移试验证明，激活蛋白-1转录调节复合物的活性在体内呈现出一种节律，这种节律在时间上与褪黑素合成的节律相关。因此，夜间激活蛋白-1活性（23:00时）显著升高，比光期活性水平高8倍（P<0.005）。夜间激活蛋白-1蛋白复合物是通过一种跨突触的、β-肾上腺素能受体相关机制诱导产生的，其特征是JunB的参与时间延长，这是使用针对特定激活蛋白-1蛋白的抗体所证明的。事实上，JunB似乎是激活蛋白-1活性夜间变化的主要成分，JunD形成了另一个组成成分，不受夜间肾上腺素能信号的影响。与JunB协同诱导的α1-肾上腺素能受体相关的c-Fos蛋白，并不是夜间激活蛋白-1活性的稳定成分。相反，平行实验表明，c-Fos确实是海马激活蛋白-1复合物的主要成分，该复合物在大鼠经 kainic 酸处理后被诱导产生。在松果体中，用去甲肾上腺素处理培养的腺体后，也证明了类似但不完全相同的激活蛋白-1激活模式。免疫印迹法已证明，在体内和体外刺激后，JunB和c-Fos蛋白在松果体细胞核部分平行积累。这些结果提供了神经递质刺激的激活蛋白-1蛋白复合物转录后选择的证据，这一机制补充了松果体中fos和jun基因的差异诱导，并有助于产生一种特定的激活蛋白-1转录因子复合物。这一发现对神经元系统中fos和jun基因诱导的功能解释具有普遍意义。这里所证明的稳定的JunB复合物可被视为一种计时机制的一个组成部分，该机制作用于使突触信号持久化，从而维持松果体夜间功能的适当周期。
