Abstract
Various growth factors influence mammalian development by binding to specific cell surface receptors. These interactions are followed by a series of intracellular transductional events leading to a wide variety of biological effects. To establish the role of insulin-like growth factor I receptor (IGF-IR) in renal development, cDNA for the alpha subunit of the mouse IGF-IR was isolated, characterized, and used in expression studies and antisense experiments in a metanephric organ culture system. A 989-bp insert, encoding the signal peptide and 299 amino acids, isolated from a newborn mouse kidney cDNA library had 99% and 91% homology with the nucleotide sequences encoding the rat and the human IGF-IR, respectively. An approximately 11-kb message was readily detected by Northern blot analysis of RNA from the developing kidney at day 13 of gestation, and it declined during the subsequent embryonal and neonatal periods. In situ hybridization revealed high levels of message over the ureteric bud and its branches. A lower level of message was seen in the neonatal kidney, confined mainly to the tubules. Antisense oligodeoxynucleotide-treated metanephric kidneys were reduced in size and had a decreased population of nephrons with marked disorganization of ureteric bud branches. Immunofluorescence studies indicated an arrest of IGF-IR translation after antisense exposure. Immunoprecipitation studies showed a marked decrease in the biosynthesis of various extracellular matrix proteins that serve as regulators of morphogenesis. These studies suggest that the nucleotide sequence encoding the alpha subunit of mouse IGF-IR is highly conserved and that the receptor might play an essential role in the organogenesis of the kidney.