The role of thyroid hormone action in the developing brain and the mechanism generating critical period of its action.

本研究以啮齿动物小脑为模型系统，探讨甲状腺激素(TH)对脑发育的影响及其作用关键期的产生机制。虽然TH受体在成年小脑中的表达较高，但与小脑发育期间相比，对TH的敏感性较低。因此，除tr以外的未知因素可能调节其敏感性。因此，我们通过免疫组织化学方法研究了发育中大鼠脑内转录调节因子SRC-1表达的个体变化。SRC-1在Purkinje细胞中强表达。在内层颗粒细胞中也有弱表达。经Western印迹分析，SRC-1蛋白在TH敏感度最高的出生后第14天表达水平最高。同时，我们尝试利用Ras-SOS酵母双杂交技术，克隆了胎儿小脑中新的转录因子受体结合蛋白。我们已经确定了一种被称为OVCOV-1的蛋白质。该蛋白全长365个氨基酸。通过序列分析，我们发现了三个负责与核受体结合的LxxLL基序。由于先前的研究表明，围产期暴露于几种环境化学物质可能会导致类似于甲状腺功能减退症的异常脑发育，因此我们研究了多氯联苯对TR介导的转录的影响。低剂量(100 PM)的多氯联苯抑制了tr介导的转录。多氯联苯的作用是通过部分解离tR与DNA的TH反应元件实现的。

The aim of this study was to investigate the effect of thyroid hormone(TH) on brain development and the mechanisms generating the critical period of its action, using a rodent cerebellum as a model system.Although the expression of TH receptor(TR) is greater in adult cerebellum, the sensitivity to TH is much less compared to that during cerebellar development. Thus, unknown factor other than TR may regulate its sensitivity. Thus, we investigated the ontogenic changes in the expression of SRC-1 that is a coactivator of TR to regulate transcription, by immunohistochemistry in the developing rat brain. SRC-1 was strongly expressed in the Purkinje cell. It was also weakly expressed in the internal granule cells. By Western blot, the level of SRC-1 protein was greatest at postnatal day (P) 14, the period when TH sensitivity is greatest.Simultaneously, we have tried to clone the novel TR-binding protein in the fetal cerebellum, using Ras-Sos yeast two hybrid screening. We have identified a protein that has been known as OVCOV-1. The size of this protein is 365 amino acid in length. By sequence analysis, we found that three LXXLL motiefs that are responsible for binding to nuclear receptors.Since previous studies have shown that perinatal exposure to several environmental chemical may induce abnormal brain development similar to those seen in hypothyroidism, we have examined the effect of polychlorinated biphenyls on TR-mediated transcription. Low dose (100 pM) PCB suppressed TR-mediated transcription. The effect of PCB was exerted by partial dissociation of TR from TH-responsive element of DNA.