Expression of IGF-II, the IGF-II/Mannose-6-Phosphate Receptor and IGFBP-2 During Rat Embryogenesis
It is becoming increasingly apparent that the IGF system (including both IGF-I and IGF-II, at least two IGF receptors, and a family of at least six IGF binding proteins; 1-3) has a fundamental role in the normal progression of prenatal development. The initial observation that IGF-II peptide levels were high in the fetus but decreased post-natally (4) was the first to suggest that this peptide might have functional importance during ontogeny. In situ hybridization studies (5-7) extended Northern analysis and confirmed that the developmental regulation of IGF-II expression extends to the level of RNA regulation and demonstrated that the IGF-II gene expression pattern during ontogeny is precisely regulated both temporally and spatially. These results suggested that if the autocrine-paracrine mode of action classically proposed for the IGFs (1,2) was in fact correct, then interference with normal IGF-II synthesis would be expected to produce regional rather than systemic deficits.
KeywordsApical Ectodermal Ridge Surface Ectoderm Hyoid Arch Nasal Placode Embryonic Epiblast
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