Schwartz W J, Carpino A, de la Iglesia H O, Baler R, Klein D C, Nakabeppu Y, Aronin N
Department of Neurology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA.
Neuroscience. 2000;98(3):535-47. doi: 10.1016/s0306-4522(00)00140-8.
Extensive studies have established that light regulates c-fos gene expression in the suprachiasmatic nucleus, the site of an endogenous circadian clock, but relatively little is known about the expression of genes structurally related to c-fos, including fra-1, fra-2 and fosB. We analysed the photic and temporal regulation of these genes at the messenger RNA and immunoreactive protein levels in rat suprachiasmatic nucleus, and we found different expression patterns after photic stimulation and depending on location in the ventrolateral or dorsomedial subdivisions. In the ventrolateral suprachiasmatic nucleus, c-fos, fra-2 and fosB expression was stimulated after a subjective-night (but not subjective-day) light pulse. Expression of the fra-2 gene was prolonged following photic stimulation, with elevated messenger RNA and protein levels that appeared unchanged for at least a few hours beyond the c-fos peak. Unlike c-fos and fra-2, the fosB gene appeared to be expressed constitutively in the ventrolateral suprachiasmatic nucleus throughout the circadian cycle; immunohistochemical analysis suggested that delta FosB was the protein product accounting for this constitutive expression, while FosB was induced by the subjective-night light pulse. In the dorsomedial suprachiasmatic nucleus, c-fos and fra-2 expression exhibited an endogenous circadian rhythm, with higher levels during the early subjective day, although the relative abundance was much lower than that measured after light pulses in the ventrolateral suprachiasmatic nucleus. Double-label immunohistochemistry suggested that some of the dorsomedial cells responsible for the circadian expression of c-Fos also synthesized arginine vasopressin. No evidence of suprachiasmatic nucleus fra-1 expression was found. In summary, fos family genes exhibit differences in their specific expression patterns in the suprachiasmatic nucleus, including their photic and circadian regulation in separate cell populations in the ventrolateral and dorsomedial subdivisions. The data, in combination with our previous results [Takeuchi J. et al. (1993) Neuron 11, 825-836], suggest that activator protein-1 binding sites on ventrolateral suprachiasmatic nucleus target genes are constitutively occupied by DeltaFosB/JunD complexes, and that c-Fos, Fra-2, FosB and JunB compete for binding after photic stimulation. The differential regulation of fos family genes in the ventrolateral and dorsomedial suprachiasmatic nucleus suggests that their circadian function(s) and downstream target(s) are likely to be cell specific.
大量研究已证实，光可调节视交叉上核（内源性昼夜节律钟的所在部位）中的c-fos基因表达，但对于与c-fos结构相关的基因（包括fra-1、fra-2和fosB）的表达了解相对较少。我们在大鼠视交叉上核中，从信使核糖核酸和免疫反应性蛋白水平分析了这些基因的光调节和时间调节，发现在光刺激后以及根据其在腹外侧或背内侧亚区的位置不同，它们具有不同的表达模式。在腹外侧视交叉上核中，主观夜间（而非主观白天）的光脉冲刺激后可诱导c-fos、fra-2和fosB的表达。光刺激后fra-2基因的表达持续延长，信使核糖核酸和蛋白水平升高，且在c-fos峰值之后至少几个小时内仍保持不变。与c-fos和fra-2不同，fosB基因在腹外侧视交叉上核的整个昼夜周期中似乎都呈组成性表达；免疫组织化学分析表明，δFosB是负责这种组成性表达的蛋白产物，而FosB则由主观夜间光脉冲诱导产生。在背内侧视交叉上核中，c-fos和fra-2的表达呈现内源性昼夜节律变化，在主观白天早期水平较高，尽管其相对丰度远低于腹外侧视交叉上核光脉冲刺激后的测量值。双重标记免疫组织化学表明，一些负责c-Fos昼夜节律表达的背内侧细胞也合成精氨酸加压素。未发现视交叉上核中有fra-1表达的证据。总之，fos家族基因在视交叉上核中的特定表达模式存在差异，包括它们在腹外侧和背内侧亚区不同细胞群体中的光调节和昼夜调节。这些数据与我们之前的结果[竹内J.等人（1993年）《神经元》11卷，825 - 836页]相结合，表明腹外侧视交叉上核靶基因上的激活蛋白-1结合位点被DeltaFosB/JunD复合物组成性占据，且c-Fos、Fra-2、FosB和JunB在光刺激后会竞争结合。腹外侧和背内侧视交叉上核对fos家族基因的差异调节表明，它们的昼夜功能和下游靶点可能具有细胞特异性。
