Thyroid hormone control of a gene expression network

甲状腺激素对基因表达网络的控制

• 批准号: 7006600
• 负责人: JOHN DAVID FURLOW
• 金额: $ 18.49万
• 依托单位: UNIVERSITY OF CALIFORNIA AT DAVIS
• 依托单位国家: 美国
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-05-15 至 2009-01-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7006600
• 关键词: DNA footprinting; Xenopus; apoptosis; binding sites; biological models; developmental genetics; gel mobility shift assay; gene expression; gene induction /repression; genetic enhancer element; genetic promoter element; genetic regulation; genetic regulatory element; genetically modified animals; hormone receptor; hormone regulation /control mechanism; metamorphosis; model design /development; molecular cloning; nucleic acid sequence; receptor expression; reporter genes; thyroid hormones; transcription factor

DESCRIPTION (provided by applicant): An important model system for understanding nuclear receptor signaling during development is metamorphosis of the frog Xenopus laevis. Thyroid hormone induces remarkable functional and morphogenetic changes as the larval tadpole transitions into the adult frog. A great deal of progress has been made on the molecular mechanisms of thyroid hormone receptor function in all vertebrates. Besides characterization of the highly conserved thyroid hormone receptor genes themselves, several receptor interacting proteins have been identified that mediate their ability to repress or activate transcription in the absence or presence of ligand, respectively. These coactivators and corepressors, collectively termed coregulators, recruit complexes that modify target gene chromatin or modulate RNA polymerase II access to hormone responsive promoters. Differential expression and/or activity of coregulator complexes have been suggested to influence cell and promoter specific responses to a given hormone, but these experiments have mostly relied on transient transfection and in vitro transcription systems or gene knockout technologies that deprive the animal of these genes from fertilization onward. Our central hypothesis is that the balance of ligand-dependent coactivation and ligand-independent corepression is critical for proper temporal and spatial responses to thyroid hormone during metamorphosis. To test this hypothesis, we will develop transgenic tadpoles that allow us to determine the precise pattern of thyroid hormone receptor mediated transcription in living tadpoles. We will then correlate coactivator and corepressor gene expression with the onset of developmental competence to respond to natural and synthetic Iigands and the tissue specificity of those responses. The relative importance of corepressor and coactivator interactions with the thyroid hormone receptor in vivo will then be tested by two strategies: first, by treatment with NH-3, a compound that disrupts both coactivator and corepressor interaction with the thyroid hormone receptor; and second, by tissue specific and inducible expression of full-length and dominant negative corepressor proteins. Finally, we will analyze gene expression networks regulated by TH in proliferating regions of the brain and jaw cartilage. We are particularly interested in determining the molecular basis for the selective agonism of NH-3 on neuronal versus cartilage proliferation. This selective agonism/antagonism is a common feature of estrogen receptor modulators such as tamoxifen but has not been previously described for thyroid hormone receptors. These last studies will provide new information on gene expression cascades leading to cellular proliferation in two tissues that are dependent on TH for proper development in both amphibians and mammals, including humans. In summary, Xenopus laevis metamorphosis is a powerful model for determining the role of thyroid hormone receptors and their coregulators in tissue specific control of gene expression networks during vertebrate development.

描述（由申请人提供）：了解发育过程中核受体信号传导的一个重要模型系统是非洲爪蟾的变态。甲状腺激素诱导显着的功能和形态发生的变化，作为幼虫蝌蚪过渡到成年青蛙。在所有脊椎动物甲状腺激素受体功能的分子机制方面已经取得了很大进展。除了对高度保守的甲状腺激素受体基因本身进行表征外，还发现了几种受体相互作用蛋白，它们分别在配体不存在或存在的情况下介导其抑制或激活转录的能力。这些辅激活子和辅阻遏子统称为辅调节子，募集复合物，修饰靶基因染色质或调节RNA聚合酶II进入激素应答启动子。已提出辅调节因子复合物的差异表达和/或活性影响细胞和启动子对给定激素的特异性反应，但这些实验大多依赖于瞬时转染和体外转录系统或基因敲除技术，这些技术从受精开始剥夺动物的这些基因。我们的中心假设是，配体依赖的共激活和配体独立的共抑制的平衡是至关重要的适当的时间和空间的反应，甲状腺激素在变态。为了验证这一假设，我们将开发转基因蝌蚪，使我们能够确定在活体蝌蚪中甲状腺激素受体介导的转录的精确模式。然后，我们将辅激活子和辅抑制子基因表达与发育能力的开始相关联，以响应天然和合成配体以及这些响应的组织特异性。辅阻遏物和辅激活物与甲状腺激素受体在体内的相互作用的相对重要性，然后将通过两种策略进行测试：第一，通过治疗与NH-3，一种化合物，破坏辅激活物和辅阻遏物与甲状腺激素受体的相互作用;第二，通过组织特异性和诱导表达的全长和显性负辅阻遏蛋白。最后，我们将分析基因表达网络的TH在大脑和颌骨软骨的增殖区域调节。我们特别感兴趣的是确定NH-3对神经元与软骨增殖的选择性激动作用的分子基础。这种选择性激动/拮抗作用是雌激素受体调节剂（如他莫昔芬）的共同特征，但以前未描述过甲状腺激素受体。这些最后的研究将提供新的信息，基因表达级联导致细胞增殖的两个组织是依赖于TH在两栖动物和哺乳动物，包括人类的正常发展。总之，非洲爪蟾变态是一个强大的模型，用于确定甲状腺激素受体及其共调节因子在脊椎动物发育过程中组织特异性控制基因表达网络的作用。