Yao Meng, Schulkin Jay, Denver Robert J
Department of Molecular, Cellular and Developmental Biology, The University of Michigan, 830 North University Avenue, Ann Arbor, Michigan 48109-1048, USA.
Endocrinology. 2008 May;149(5):2352-60. doi: 10.1210/en.2007-1551. Epub 2008 Jan 17.
Glucocorticoids (GCs) exert feedback regulation on corticotropin-releasing factor (CRF) neurons in mammals. The nature of GC actions is cell-type specific, being either inhibitory (e.g. paraventricular nucleus) or stimulatory (e.g. amygdala and bed nucleus of the stria terminalis). Nothing is known about differential regulation of CRF gene expression by GCs in nonmammalian vertebrates. We studied the actions of GCs on CRF expression in discrete brain regions of the frog Xenopus laevis. Treatment with corticosterone (CORT) decreased, whereas the corticosteroid synthesis inhibitor metyrapone increased CRF expression in the anterior preoptic area (homolog of the mammalian paraventricular nucleus), as measured by CRF primary transcript, mRNA, and CRF immunoreactivity (ir) (by immunocytochemistry). By contrast to the preoptic area, CORT increased CRF-ir in the medial amygdala and bed nucleus of the stria terminalis, whereas metyrapone decreased CRF-ir in the medial amygdala. CRF-ir and glucocorticoid receptor-ir were colocalized in cells in the frog brain. In transient transfection assays in PC-12 cells, GCs decreased forskolin-induced activation of the frog CRF promoters. Treatment with CORT also reduced CRF promoter activity in transfected tadpole brain in vivo. Frog glucocorticoid receptor bound with high-affinity in vitro to regions in the proximal promoters of frog CRF genes that are homologous with the human CRF gene. Our findings suggest that the neural cell-type specificity and molecular mechanisms of GC-dependent regulation of CRF are phylogenetically ancient, and that the limbic pathways mediating behavioral and physiological responses to stressors were likely present in the earliest land-dwelling vertebrates.
糖皮质激素（GCs）对哺乳动物的促肾上腺皮质激素释放因子（CRF）神经元发挥反馈调节作用。GC作用的性质具有细胞类型特异性，既可以是抑制性的（如室旁核），也可以是刺激性的（如杏仁核和终纹床核）。关于非哺乳动物脊椎动物中GCs对CRF基因表达的差异调节尚无相关研究。我们研究了GCs对非洲爪蟾（Xenopus laevis）离散脑区中CRF表达的作用。通过CRF初级转录本、mRNA和CRF免疫反应性（ir）（免疫细胞化学法）检测发现，用皮质酮（CORT）处理会降低前视前区（哺乳动物室旁核的同源区域）的CRF表达，而皮质类固醇合成抑制剂美替拉酮则会增加该区域的CRF表达。与视前区相反，CORT增加了内侧杏仁核和终纹床核中的CRF-ir，而美替拉酮则降低了内侧杏仁核中的CRF-ir。CRF-ir和糖皮质激素受体-ir在蛙脑的细胞中共定位。在PC-12细胞的瞬时转染实验中，GCs降低了福斯高林诱导的蛙CRF启动子的激活。用CORT处理也降低了体内转染蝌蚪脑内的CRF启动子活性。蛙糖皮质激素受体在体外与蛙CRF基因近端启动子中与人CRF基因同源的区域高亲和力结合。我们的研究结果表明，GC依赖的CRF调节的神经细胞类型特异性和分子机制在系统发育上是古老的，并且介导对应激源行为和生理反应的边缘通路可能在最早的陆地脊椎动物中就已存在。
