THYROID HORMONE RECEPTORS IN FROG METAMORPHOSIS

青蛙变态是理解胚胎后发育过程机制的一个很好的模型系统。变态过程中发生的变化由甲状腺激素(TH)控制，所有脊椎动物都会发生相关的变化。甲状腺激素受体(TRs)被认为介导了TH对变态的影响，了解它们的作用将为胚胎后发育的机制提供重要的信息。该方案中的研究实验利用简单但具有良好特征的蜕变过程--蛙肠道在体内的重塑--来研究Trs在发育过程中调节细胞命运的作用，即细胞增殖与细胞凋亡。实验方法包括应用最近开发的转基因方法和使用一系列显微、分子和细胞分析技术。转基因将使我能够改变活着的蝌蚪体内TRs的表达水平或功能，并将检测在肠道变态期间对形态转化和基因活性的影响。本文提出的实验将直接证明TRs是否以器官和/或细胞自主的方式在体内介导TH诱导的变性事件。此外，这些实验直接解决了这样的假设，即在脊椎动物的发育过程中，TRs发挥着双重功能，即在没有TH的情况下抑制TH调节的基因，在存在TH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.