DISTRIBUTION AND RELEVANCE OF INSULIN-LIKE GROWTH FACTOR-I RECEPTOR IN METANEPHRIC DEVELOPMENT

During embryogenesis, various ligand-receptor interactions take place to modulate the development and growth of various mammalian organs. Du ring these interactions, a critical concentration of a given receptor is needed to elicit a ligand-induced biologic response at a defined ge stational stage of the fetus. In this study, the distribution and the relevance of insulin-like growth factor-I receptor (IGF-IR) in metanep hric development was investigated. Kidneys were harvested from mouse e mbryos at days 13 to 19 of fetal gestation, and maintained in a metane phric culture system. Immunofluorescence studies, using anti-IGF-IR, r evealed a high expression of IGF-IR at day 13, which declined during t he later stages of gestation through neonatal life. To study the relev ance of IGF-IR expression in metanephric development, antisense-oligod eoxynucleotide (ODN) experiments were carried out. Antisense-ODN 43 me r probes were synthesized utilizing rat IGF-IR cDNA selected nucleotid e sequences which are highly conserved in other mammalian species. Sou thern blot analyses of various restriction fragments of the rat and mi ce genomic DNA yielded similar bands when hybridized with the antisens e-ODN or rat IGF-IR cDNA, suggesting a high degree of homology in the region of the gene selected for the synthesis of antisense-ODN. Also, the antisense-ODN hybridized with the appropriate murine fetal kidney mRNA species, as ascertained by S1 nuclease protection assay. Inclusio n of antisense-ODN in the culture medium resulted in an inhibition of the growth of the kidney, reduction in the population of the nephrons and disorganization of the ureteric bud branches. Effectivity of the a ntisense-ODN was reduced during the later stages of development when t he expression of IGF-IR is decreased. Immunoprecipitation studies reve aled a reduction in the IGF-IR associated radioactivity, indicating a specific translational arrest. These studies suggest that IGF-IR is re levant in the modulation of various developmental events during the ea rly midgestational period, the time when it is highly expressed in the metanephric tissues.