Developmental regulation of the rat insulin-like growth factor I receptor gene

We have invetigated the developmental regulation of the rat insulin-like growth factor I (IGF-I) receptor gene in various tissue using a sensitive and specific solution hybridization/RNase protection assay. For this purpose we characterized rat IGF-I receptor cDNAs that were cloned from a simian virus 40-transformed rat granulosa cell cDNA library. The specific cDNA clone used in these studies encoded the putative signal peptide and the first 53 amino acids of the α subunit and was ~94% homologous to its human counterpart. IGF-I receptor gene expression was studied during the perinatal period and at various intervals until early adulthood. Overall, steady-state IGF-I receptor mRNA levels decreased dramatically during postnatal development; however, the extent of the decrease differed among the various tissues studied. In contrast to receptor mRNA levels, IGF-I mRNA levels increased in some of the same tissues. The molecular mechanisms underlying this apparent divergent transcriptional control of the IGF-I and IGF-I receptor genes warrant further study.