Regulation of the insulin-like growth factor system during normal rat lung development

Insulin-like growth factor (IGF)-I and IGF-II are small peptide growth factors that interact with a specific membrane receptor, the type 1 IGF receptor, to stimulate cellular proliferation and/or differentiation. The actions of these growth factors and their availability to their receptors are modulated by specific binding proteins, IGF binding protein (IGFBP)-1 through -6, which together with the IGFs and IGF receptors form the IGF system. We have analyzed RNA extracted from fetal (gestation day 16 [E16] through 22 [E22]) and adult (60-day-old) rat lung for expression of each component of the IGF system. IGF-I and -II RNAs are expressed throughout fetal development. IGF-I mRNA remained relatively constant in fetal and adult lung, whereas IGF-II RNA decreased in later gestation to levels below detection by Northern analyses in adult lung. Type 1 IGF receptor expression varied little through all ages studied, whereas the type 2 IGF receptor RNA displayed developmental regulation with a decline in expression with advancing age. IGFBP-1 transcripts were not detected in fetal or adult lung. IGFBP-2 RNA was expressed from E16 to E22, although its abundance decreased in late gestation and in adult lung, with the lowest levels of expression on day E22. IGFBP-3, -4, and -5 had similar profiles of RNA abundance, with fetuses at ages E21 and E22 displaying higher levels of transcript abundance as compared with those aged E17 to E20; the lowest RNA abundance was seen at E20.(ABSTRACT TRUNCATED AT 250 WORDS)