ROLE OF ENDOCRINE SECRETIONS IN GROWTH AND DEVELOPMENT

IGF-I发挥广泛的内分泌、旁分泌或自分泌作用 对多个细胞和组织的作用。在大鼠和其他哺乳动物中 物种，由单一基因衍生的IGF-I mRNAs的复杂家族。 我们的中心假设是IGF-I mRNAs和 编码的前体是IGF-I发挥其功能所不可或缺的 行动的多样性。 不同的IGF-I mRNAs编码的不同的IGF-I前体可以 确定IGF-I的胞内或胞外靶点 作用或可能影响IGF-I与受体或结合的相互作用 蛋白质。拟议的研究将通过(I)检验这些可能性 定义由翻译而来的IGF-I的结构 不同的mRNAs(II)分析细胞内定位、加工和 培养细胞系统中IGF-I前体的分泌(III)模型 细胞系统和转基因小鼠以评估其生物学行为 IGF-I前体。转基因小鼠代表着独特的模型来研究 地球表面扰动的发展和长期后果 特异性IGF-I前体的合成。我们的目标是针对生长激素 (Gh)特异性IGF-I受体在肝脏的独立表达， 循环IGF-I的主要来源，并分析这种靶向是否可以 纠正生长激素和IGF-I缺陷小鼠的生长迟缓。这将是 解决IGF-I生理学中的两个核心问题：IGF-I在 不依赖生长激素刺激生长和循环的贡献 与局部合成的IGF-I刺激躯体和组织的比较 在发展中成长。 转录和转录后调控机制 不同的IGF-I mRNAs的表达可决定IGF-I的作用部位、水平 和IGF-I表达的时间进程，从而确定IGF-I表达的地点和时间 IGF-I行动的进程。我们将通过(I)来分析这些机制 调节胰岛素样生长因子-I的生长激素依赖性启动子(S)的特征 转录水平上的合成(II)评估 转录后调控IGF-I在mRNA水平的合成 稳定性。我们已经证明了大分子形式的IGF-I 带有长3‘非翻译区的信使核糖核酸(3’UT)不如 较小的表格。因此，我们将定义中介序列 这些mRNAs的不稳定性，确定了糖皮质激素 破坏这些mRNAs的稳定性以及这是否会导致IGF-I减少 综合。

IGF-I exerts a wide spectrum of endocrine, paracrine or autocrine actions on multiple cells and tissues. In rat and other mammalian species, a complex family of IGF-I mRNAs derived from a single gene. Our central hypothesis is that the heterogeneity of IGF-I mRNAs and encoded precursors is integral to tbe ability of IGF-I to exert its diversity of actions. Different IGF-I precursors encoded by different IGF-I mRNAs could determine targeting of IGF-I to intracellular or extracellular sites of action or could influence IGF-I interactions with receptors or binding proteins. Proposed studies will test these possibilities by (i) defining the structures of the IGF-I that result from translation of different mRNAs (ii) analysing intracellular localiation, processing and secretion of IGF-I precursors in cultured cell systems (iii) using model cell systems and transgenic mice to assess the biological actions of IGF-I precursors. Transgenic mice represent unique models to study the developmental and long term consequences of perturbations in the synthesis of specific IGF-I precursors. We aim to target growth hormone (GH) independent expression of specific IGF-I pecursors to liver, the major source of circulating IGF-I and analyse whether such targeting can correct growth retardation in GH and IGF-I deficient mice. This will address two central questions in IGF-I physiology: the role of IGF-I in stimulating growth independent of GH and the contribution of circulating versus locally synthesized IGF-I in stimulating somatic and tissue growth during development. Transcriptional and post-transcriptional mechanisms that regulate the expression of different IGF-I mRNAs could determine the sites, levels and time course of IGF-I expression and thereby the locus and time course of IGF-I action. We will analysc these mechanisms by (i) characterizing the GH dependent promotor (s) that regulate IGF-I synthesis at the level of transcription (ii) assessing post-transcriptional control of IGF-I synthesis at the level of mRNA stability. We have demonstrated that large molecular forms of IGF-I mRNA with long 3'untranslated regions (3'UTs) are less stable than smaller forms. We will therefore define the sequences that mediate instability of these mRNAs, establish whether glucocorticoids destabilize these mRNAs and whether this results in reduced IGF-I synthesis.