Division of Endocrinology, Metabolism, and Diabetes, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, E/CLS-0738, Boston, Massachusetts 02215, USA.
Endocrinology. 2010 Feb;151(2):793-801. doi: 10.1210/en.2009-0976. Epub 2009 Dec 23.
The expression of the TRH gene in the paraventricular nucleus (PVH) of the hypothalamus is required for the normal production of thyroid hormone (TH) in rodents and humans. In addition, the regulation of TRH mRNA expression by TH, specifically in the PVH, ensures tight control of the set point of the hypothalamic-pituitary-thyroid axis. Although many studies have assumed that the regulation of TRH expression by TH is at the level of transcription, there is little data available to demonstrate this. We used two in vivo model systems to show this. In the first model system, we developed an in situ hybridization (ISH) assay directed against TRH heteronuclear RNA to measure TRH transcription directly in vivo. We show that in the euthyroid state, TRH transcription is present both in the PVH and anterior/lateral hypothalamus. In the hypothyroid state, transcription is activated in the PVH only and can be shut off within 5 h by TH. In the second model system, we employed transgenic mice that express the Cre recombinase under the control of the genomic region containing the TRH gene. Remarkably, TH regulates Cre expression in these mice in the PVH only. Taken together, these data affirm that TH regulates TRH at the level of transcription in the PVH only and that genomic elements surrounding the TRH gene mediate its regulation by T(3). Thus, it should be possible to identify the elements within the TRH locus that mediate its regulation by T(3) using in vivo approaches.
在下丘脑的室旁核 (PVH) 中，TRH 基因的表达是啮齿动物和人类甲状腺激素 (TH) 正常产生所必需的。此外，TH 对 TRH mRNA 表达的调节，特别是在 PVH 中的调节，确保了下丘脑-垂体-甲状腺轴设定点的紧密控制。尽管许多研究假设 TH 对 TRH 表达的调节是在转录水平上进行的，但可用的数据很少证明这一点。我们使用了两种体内模型系统来证明这一点。在第一个模型系统中，我们开发了一种针对 TRH 异核 RNA 的原位杂交 (ISH) 测定法，直接在体内测量 TRH 转录。我们表明，在甲状腺功能正常的状态下，TRH 转录既存在于 PVH 中，也存在于前/外侧下丘脑。在甲状腺功能减退状态下，转录仅在 PVH 中被激活，并且可以在 5 小时内被 TH 关闭。在第二个模型系统中，我们使用了在 TRH 基因的基因组区域控制下表达 Cre 重组酶的转基因小鼠。值得注意的是，TH 仅在这些小鼠的 PVH 中调节 Cre 表达。总之，这些数据证实，TH 仅在 PVH 中通过转录水平调节 TRH，并且 TRH 基因周围的基因组元件介导其对 T(3)的调节。因此，使用体内方法应该有可能识别介导 TRH 对 T(3)调节的 TRH 基因座内的元件。
