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 细胞水平的生长激素最初通过与细胞结合而产生作用 表面蛋白称为生长激素受体(GHR)。各种各样的 影响GHR表达的因素；GHR几乎检测不到 而在胎儿组织中，它的表达在 出生后的生活。控制发育调节性疾病的因素 GHR的表达情况尚不清楚。我发现了一种新的增强剂 小鼠生长激素受体基因启动子调控区的元件 它在肝脏中表现出发育调节的DNA结合活性。 此外，该增强子元件在瞬变中的功能活性 转染法也受发育调节。我假设 已鉴定的增强子元件及其同源反式作用因子(S) 在GHR基因的发育调控表达中发挥作用。 这一提议专门试图阐明分子机制。 控制GHR基因的发育调控表达。这个 本提案中详细说明的实验策略旨在测试 已确定的增强子元件在发育调节基因中的作用 GHR基因的定点突变表达 嵌合报告基因在胎儿和成人肝细胞中的表达 基因结构，并通过对DNase I超敏部位的定位 5‘侧翼区域。在经过初步的生化检测后 脱氧核糖核酸结合蛋白(S)的特性及其同源性 反式作用因子(S)将通过克隆编码基因确定 这些可能的转录因子的基因(S)。 这些研究将：(A)勾勒出基因改变的分子基础 生长激素受体基因在遗传性矮小等生长发育障碍中的表达 身高、宫内发育迟缓和营养不良，使 (B)设计新的诊断工具和更有效的治疗 针对这些人类生长和发育障碍的策略。

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.