THYROID HORMONE RECEPTORS IN FROG METAMORPHOSIS

青蛙变态是了解胚胎后发育过程机制的一个很好的模型系统。在变态过程中发生的变化是由甲状腺激素（TH）控制的，所有脊椎动物都会发生相关的变化。甲状腺激素受体（TRs）被认为是介导TH对变态的影响，了解其作用将为了解胚胎后发育机制提供重要信息。该提案中的研究实验利用简单但表征良好的变性过程，即体内青蛙肠的重塑来研究TRs在调节细胞命运中的作用，即，细胞增殖与凋亡。实验方法包括应用最近开发的转基因方法和使用一组显微镜、分子和细胞分析技术。转基因将使我能够改变表达水平或功能的TR在活蝌蚪，并在肠变态过程中的形态转化和基因活性所产生的影响将进行检查。本文提出的实验将直接证明TR是否以器官和/或细胞自主方式在体内介导TH诱导的变质事件。此外，这些实验直接解决了TR在脊椎动物发育期间发挥双重功能的假设，即，在TH不存在的情况下抑制TH调节的基因并在TH存在的情况下激活它们。

Frog metamorphosis is an excellent model system to understand the mechanisms of postembryonic developmental processes. The changes that occur during metamorphosis are controlled by thyroid hormone (TH), and related changes occur in all vertebrates. Thyroid hormone receptors (TRs) are presumed to mediate the effects of TH on metamorphosis and understanding their role will provide important information about the mechanisms of post-embryonic development. Research experiments in this proposal take advantage of the simple but well-characterized metamorphic process, the remodeling of the frog intestine in vivo to investigate the roles of TRs in regulating cell fate, i.e., cell proliferation vs. apoptosis, during development. The experimental approaches involve the application of the recently developed transgenic methodologies and the use of a battery of microscopic, molecular and cellular analysis techniques. Transgenesis will allow me to alter expression levels or the function of TRs in living tadpoles, and the resulting effects on morphological transformation and gene activity during intestinal metamorphosis will be examined. The experiments proposed herein will directly demonstrate whether TRs mediate TH- induced metamorphic events in vivo in an organ and/or cell autonomous fashion. In addition, these experiments directly address the hypothesis that TRs play dual functions during vertebrate development, i.e., repressing TH-regulated genes in the absence of TH and activating them in the presence of TH.