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. During these interactions, a critical concentration of a given receptor is needed to elicit a ligand-induced biologic response at a defined gestational stage of the fetus. In this study, the distribution and the relevance of insulin-like growth factor-I receptor (IGF-IR) in metanephric development was investigated. Kidneys were harvested from mouse embryos at days 13 to 19 of fetal gestation, and maintained in a metanephric culture system. Immunofluorescence studies, using anti-IGF-IR, revealed a high expression of IGF-IR at day 13, which declined during the later stages of gestation through neonatal life. To study the relevance of IGF-IR expression in metanephric development, antisense-oligodeoxynucleotide (ODN) experiments were carried out. Antisense-ODN 43 mer probes were synthesized utilizing rat IGF-IR cDNA selected nucleotide sequences which are highly conserved in other mammalian species. Southern blot analyses of various restriction fragments of the rat and mice genomic DNA yielded similar bands when hybridized with the antisense-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. Inclusion 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 antisense-ODN was reduced during the later stages of development when the expression of IGF-IR is decreased. Immunoprecipitation studies revealed a reduction in the IGF-IR associated radioactivity, indicating a specific translational arrest. These studies suggest that IGF-IR is relevant in the modulation of various developmental events during the early midgestational period, the time when it is highly expressed in the metanephric tissues.