FETAL/POSTNATAL REGULATION OF GH RECEPTOR EXPRESSION

生长激素（GH）是动物出生后生长所必需的。在 细胞水平GH通过最初与细胞结合来发挥其作用 生长激素受体（GHR）是一种被称为生长激素受体的表面蛋白。各种 影响GHR表达的因素; GHR几乎检测不到 在胎儿组织中，它的表达在胚胎发育过程中显著增加， 产后生活发展性管制的控制因素 GHR的表达是未知的。我发现了一种新的增强剂 小鼠GH受体基因启动子调控区元件 其在肝脏中表现出发育调节的DNA结合活性。 此外，该增强子元件在瞬时表达中的功能活性也被证实。 转染测定也是受发育调控的。我假设 鉴定的增强子元件及其同源反式作用因子 在GHR基因的发育调控表达中发挥作用。 该提案旨在明确阐明分子机制 控制GHR基因的发育调节表达。的 本提案中详细介绍的实验策略旨在测试 鉴定的增强子元件在发育调节的 通过定点突变瞬时表达GHR基因 使用嵌合报告基因的胎儿和成人肝细胞的转染测定 基因构建，并通过绘制DNase I超敏位点， 5’侧翼区。经过初步的生化检查 DNA结合蛋白的表征，这些DNA结合蛋白的身份， 将通过克隆编码以下的cDNA来确定反式作用因子： 这些假定的转录因子的基因。 这些研究将（a）描绘改变的分子基础， GHR基因在生长障碍中的表达，例如遗传性短 身高、子宫内生长迟缓和营养不良， （B）设计新的诊断工具和更有效的治疗方法 为这些人类生长和发育障碍的战略。

Growth hormone (GH) is essential for postnatal growth in animals. At the cellular level GH elicits its actions by initially binding to a cell surface protein termed the growth hormone receptor (GHR). A variety of factors influence the expression of the GHR; GHR is virtually undetectable in fetal tissues while its expression increases dramatically during postnatal life. The factors controlling the developmentally-regulated expression of the GHR are not known. I have identified a novel enhancer element in the promoter-regulatory region of the murine GH receptor gene which exhibits developmentally-regulated DNA-binding activity in liver. Furthermore, the functional activity of this enhancer element in transient transfection assays is also developmentally-regulated. I HYPOTHESIZE that the identified enhancer element with its cognate trans-acting factor(s) play a role in the developmentally-regulated expression of the GHR gene. This proposal seeks SPECIFICALLY to elucidate the molecular mechanisms controlling the developmentally-regulated expression of the GHR gene. The experimental strategy detailed in this proposal is designed to test the role of the identified enhancer element in the developmentally-regulated expression of the GHR gene by site-directed mutagenesis, transient transfection assays of fetal and adult hepatocytes using chimeric reporter gene constructs, and by mapping of the DNase I hypersensitivity sites in the 5' flanking region. Following a preliminary biochemical characterization of the DNA-binding protein(s), the identity of these trans-acting factor(s) will be ascertained by cloning the cDNA encoding the genes for these putative transcription factor(s). These studies will (a) delineate the molecular basis for alterations in expression of the GHR gene in disorders of growth such as genetic short stature, intra-uterine growth retardation and malnutrition, enabling (b)the design of novel diagnostic tools and more effective treatment strategies for these disorders of growth and development in the human.