Hayward M A, Brock M L, Shapiro D J
Am J Physiol. 1982 Jul;243(1):C1-6. doi: 10.1152/ajpendo.1982.243.1.E1.
Administration of estradiol 17 beta [estra-1,3,5(10)-triene-3,17-beta-diol] to male Xenopus laevis induces the massive synthesis by the liver of the egg yolk precursor phospholipoglycoprotein, vitellogenin, and its cognate mRNAs. Restimulation of male X. laevis that have been previously induced to synthesize vitellogenin mRNA but are inactive in vitellogenin mRNA synthesis at the time of restimulation with estrogen results in more rapid accumulation of vitellogenin mRNA and more efficient transcription of the vitellogenin genes than occurs following primary estrogen stimulation. The estrogen receptor system that mediates estrogen action in this organism exhibits several unusual properties. The cytoplasm of unstimulated liver cells contains high levels of a middle-affinity estrogen-specific binding protein and little if any estrogen receptor. The properties of the estrogen binding protein are consistent with a role in protecting estradiol 17 beta against metabolism, as a fraction of cytoplasmic estradiol 17 beta is not subject to rapid metabolism. In addition, similar binding activities are found in all Xenopus tissues surveyed that respond to steroid hormones. The induction of nuclear estrogen receptor is coincident with the onset of vitellogenin mRNA accumulation. However, an increased level of estrogen receptor is not responsible for the elevated rate of vitellogenin gene transcription observed following restimulation with estrogen.
给雄性非洲爪蟾施用17β-雌二醇[estra-1,3,5(10)-三烯-3,17-β-二醇]可诱导肝脏大量合成卵黄前体磷脂糖蛋白、卵黄蛋白原及其同源mRNA。对先前已被诱导合成卵黄蛋白原mRNA但在用雌激素再次刺激时卵黄蛋白原mRNA合成无活性的雄性非洲爪蟾进行再次刺激，与初次雌激素刺激相比，会导致卵黄蛋白原mRNA更快积累以及卵黄蛋白原基因转录更高效。介导该生物体中雌激素作用的雌激素受体系统表现出几种不同寻常的特性。未受刺激的肝细胞胞质中含有高水平的中等亲和力雌激素特异性结合蛋白，几乎没有雌激素受体。雌激素结合蛋白的特性与保护17β-雌二醇免受代谢的作用一致，因为一部分胞质17β-雌二醇不受快速代谢的影响。此外，在所有接受调查的对类固醇激素有反应的非洲爪蟾组织中都发现了类似的结合活性。核雌激素受体的诱导与卵黄蛋白原mRNA积累的开始同时发生。然而，雌激素再次刺激后观察到的卵黄蛋白原基因转录速率升高并非由雌激素受体水平升高所致。
