THE HORMONAL CONTROL OF FETAL GROWTH

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This proposal is based on the hypothesis that the Insulin-like Growth Factors (IGF-I and IGF-II) are essential to the regulation of embryonic and fetal growth and development. We postulate that the IGFs, IGF receptors, and IGF binding proteins (IGFBPs) are expressed from early in embryogenesis, and that the time of onset and control of expression of these proteins differs depending on the stage of cellular maturation. Furthermore, because the IGFs have diverse biologic effects, we believe that all IGF in utero actions have not been defined. The goals of this proposal therefore, are to determine the time of inset of IGF, IGF receptor and IGFBP expression; to elucidate the factors that regulate IGFs in utero; and to define IGF actions and mechanisms of action important to development. Specifically, we will determine the ontogeny and sites of expression of the IGFs, IGF receptors and IGFBPs from pre-implantation embryogenesis through neonatal life in rats and mice (Spec. Aim 1). To define the regulation IGF, IGF receptor and IGFBP expression during in utero and neonatal development (Spec. Aim 2), we will assess the factors that modulate in vitro expression in embryonal carcinoma cell lines and in cultured fetal and neonatal rat fibroblasts. We also will evaluate in vivo expression of IGFs, IGF receptors and IGFBPs in tissues of fetal rats subjected to perturbations that result in intrauterine growth retardation and to the administration of substances found to alter the expression of these proteins in vitro. To determine the factors that stimulate IGF transcription (Spec. Aim 3), we will study the regulation of expression of fusion genes linking IGF 5' genomic flanking elements to reporter genes in stably transfected cultured cells and transgenic mice. Using a number of transgenes designed to alter IGF expression, we will study in utero actions and mechanisms of action of IGFs in cultured stably transfected cells (Spec. Aim 4) and transgenic mice (Spec. aim 5). To investigate IGF actions, we will: a) create IGF-I expression in embryonic and fetal- derived cells that do not normally express IGF-I using transgenes that fuse either the metallothionein promoter or the mIGF-II genomic 5' flanking region to an IGF-IA gene, b) generate in utero IGF-I overexpression in transgenic mice using the fusion of MIGF-II 5' flanking IGFs and in transgenic mice using fusion genes that express anti-sense IGF transcripts or ribozymes that specifically cleave IGF transcripts. To examine the mechanisms of IGF-I's actions, we will: a) examine changes in the expression of IGF receptors and IGFBPs as a consequence of each of the above alterations in IGF expression, b) test IGF-I's potential autocrine actions, using transgenes expressing mutant IGF-I molecules that are not secreted either because they have amino acid (KDEL) trailer sequence targeting the endoplasmic reticulum or because they lack a signal peptide, and c) determine the effect of IGFBP-1 expression on IGF actions by study of cultured cells and transgenic mice made to express transgenes encoding hBP-1 and an anti-sense hBP-1 transcript (Spec. Aim 6).