Opitz Robert, Trubiroha Achim, Lorenz Claudia, Lutz Ilka, Hartmann Sabine, Blank Tobias, Braunbeck Thomas, Kloas Werner
Department of Inland Fisheries, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Mueggelseedamm 310, D-12587 Berlin, Germany.
J Endocrinol. 2006 Jul;190(1):157-70. doi: 10.1677/joe.1.06606.
The uptake of iodide represents the first step in thyroid hormone synthesis by thyroid follicular cells and is mediated by the sodium-iodide symporter (NIS). In mammals, expression of NIS is stimulated by TSH and transcription of the NIS gene involves regulation by the thyroid-specific transcription factors Pax8 and Nkx2.1. In this study, we examined the mRNA expression of NIS, Pax8 and Nkx2.1 in the thyroid gland of Xenopus laevis tadpoles by semi-quantitative reverse transcriptase (RT)-PCR. During spontaneous metamorphosis, NIS mRNA expression was low in premetamorphic tadpoles, increased throughout prometamorphosis, and peaked at climax stage 60. Analysis of TSH beta-subunit (TSHbeta) mRNA in the pituitary of the same tadpoles revealed a close temporal relationship in the expression of the two genes during metamorphosis, suggesting a regulatory role of TSH in the developmental expression of NIS. Treatment of tadpoles with goitrogenic compounds (sodium perchlorate and ethylenethiourea) increased TSHbeta mRNA expression (approximately twofold) and caused thyroid gland hyperplasia, confirming that feedback along the pituitary-thyroid axis was operative. Analysis of gene expression in the thyroid gland revealed that goitrogen treatment was correlated with increased expression of NIS mRNA (approximately 20-fold). In the thyroid gland organ culture experiments, bovine TSH (bTSH; 1 mU/ml) strongly induced NIS mRNA expression. This effect was mimicked by co-culture of thyroid glands with pituitaries from stage 58 tadpoles and by agents that increase intracellular cAMP (forskolin, dibutyryl-cAMP). In addition, it could be shown that thyroid glands of X. laevis tadpoles express Pax8 and Nkx2.1 mRNA in a developmentally regulated manner and that ex vivo treatment of thyroid glands with bTSH, forskolin, and cAMP analogs increased the expression of Pax8 and Nkx2.1 mRNA. This is the first report on developmental profiles and hormonal regulation of thyroid gland gene expression in amphibian tadpoles and, together, results reveal a critical role of TSH in the regulation of NIS mRNA expression in the thyroid gland of X. laevis tadpoles.
碘摄取是甲状腺滤泡细胞合成甲状腺激素的第一步，由钠碘同向转运体（NIS）介导。在哺乳动物中，TSH刺激NIS的表达，NIS基因的转录受甲状腺特异性转录因子Pax8和Nkx2.1的调控。在本研究中，我们通过半定量逆转录酶（RT）-PCR检测了非洲爪蟾蝌蚪甲状腺中NIS、Pax8和Nkx2.1的mRNA表达。在自发变态过程中，NIS mRNA表达在前变态期蝌蚪中较低，在整个前变态期增加，并在变态高峰期60达到峰值。对同一蝌蚪垂体中TSHβ亚基（TSHbeta）mRNA的分析显示，在变态过程中这两个基因的表达存在密切的时间关系，提示TSH对NIS的发育表达具有调节作用。用致甲状腺肿化合物（高氯酸钠和乙撑硫脲）处理蝌蚪可使TSHbeta mRNA表达增加（约两倍）并导致甲状腺增生，证实垂体-甲状腺轴的反馈作用是有效的。对甲状腺中基因表达的分析表明，致甲状腺肿处理与NIS mRNA表达增加（约20倍）相关。在甲状腺器官培养实验中，牛TSH（bTSH；1 mU/ml）强烈诱导NIS mRNA表达。58期蝌蚪的垂体与甲状腺共培养以及使用增加细胞内cAMP的试剂（福斯可林、二丁酰-cAMP）可模拟这种效应。此外，还可以证明非洲爪蟾蝌蚪的甲状腺以发育调控的方式表达Pax8和Nkx2.1 mRNA，并且用bTSH、福斯可林和cAMP类似物对甲状腺进行离体处理可增加Pax8和Nkx2.1 mRNA的表达。这是关于两栖类蝌蚪甲状腺基因表达的发育谱和激素调节的首次报道，这些结果共同揭示了TSH在调节非洲爪蟾蝌蚪甲状腺中NIS mRNA表达方面的关键作用。
