THYROID HORMONE RECEPTORS IN DEVELOPMENT

本研究员的长期研究目标是阐明 甲状腺激素（TH）在发育过程中的作用机制。 本文提出的研究目的是研究TH受体 在两栖动物牛蛙的生命发育阶段， 周期 这是这些研究的独特动物模型。 增长， 发育和变态依赖于TH，并可由 外源性TH和某些组织中的TH受体数量（位点/核）可以是 增加了TH。 越来越多的证据表明TH受体是由 编码TH结合蛋白的c-erbA cDNA具有 从哺乳动物和鸟类组织中分离出来。 其中一些会杂交 与蝌蚪组织的mRNA。 这些cDNA将用于评估数量 蝌蚪和青蛙中存在的c-erbA相关mRNA种类的大小 组织，并确定是否有发育调节 一种或多种这些物种在生命过程中的水平变化 周期 这种变化与TH的已知变化呈正相关， 在发展过程中的受体数量将支持这一假设，即一个c- erbA基因编码TH受体。 为了确定蝌蚪c-erbA基因 编码TH受体，从蝌蚪组织构建的cDNA文库将 用cDNA探针进行筛选，阳性克隆的cDNA插入片段 测序，并确定其蛋白质产物的性质。 克隆 将测试含有编码TH结合蛋白的cDNA的它们的 赋予或增强内源性低T3应答细胞的能力 TH受体。 最后，将进行研究，以确定是否TH- 在发育中的蝌蚪中诱导的受体数量增加是由于 影响相关基因的转录。 在人类发育过程中TH不足会导致永久性脑损伤， 其中最严重的表现是克汀病。 然而， 和调节TH行动在这一时期得到了相对 很少注意，部分原因是由于传导的困难， 研究胎儿哺乳动物。 拟议的研究将利用一个突出的 合适的动物模型来研究这些重要的生物学过程。

The long range research goal of this investigator is to elucidate the mechanism(s) of action of the thyroid hormones (TH) during development. The aim of the research proposed herein is to investigate the TH receptor in the amphibian Rana catesbeiana during developmental phases of the life cycle. This is a unique animal model for these studies. Growth, development and metamorphosis are dependent on TH and can be induced by exogenous TH, and TH receptor number (sites/nucleus) in some tissues can be increased by TH. Evidence is accumulating that the TH receptor is encoded by a c-erbA gene, and c-erbA cDNAs which encode TH binding proteins have been isolated form mammalian and avian tissues. Some of these hybridize with tadpole tissue mRNAs. These cDNAs will be used to assess the number and size of c-erbA-related mRNA species present in tadpole and frog tissues, and to determine whether there are developmentally-regulated changes in the levels of one or more of these species during the life cycle. A positive correlation of such changes with the known changes in TH receptor number during development will support the hypothesis that a c- erbA gene encodes the TH receptor. To determine if tadpole c-erbA genes encode a TH receptor, cDNA libraries constructed from tadpole tissues will be screened with the cDNA probes, the cDNA inserts of positive clones sequenced, and the properties of their protein products determined. Clones containing cDNAs which encode TH binding proteins will be tested for their ability to confer or enhance T3 responsiveness in cells low in endogenous TH receptor. Finally, studies will be performed to determine if the TH- induced increase in receptor number in developing tadpoles is due to an effect on the transcription of the relevant gene. Insufficient TH during human development results in permanent brain damage, the most severe manifestation of which is cretinism. Yet the mechanisms and regulation of TH action during this period have received relatively little attention, due in part to the difficulties of conduction such studies in fetal mammals. The proposed studies will utilize an eminently suitable animal model to investigate these important biological processes.