Single-chain protein growth factors that closely resemble insulin and each other in their amino acid sequences. Both IGF-1 and IGF-2 and their receptors are present as early as the eight-cell stage in the mouse, and growth is retarded if either igf-1 or igf-2 gene is inactivated. IGF-2 is essential for early embryonic growth in the mouse, but IGF-1 seems more important in the later development. The IGF-2 gene shows parental imprinting (q.v.). In Caenorhabditis the gene for the IGF-1 receptor is encoded by daf-2, and mutations of this gene cause a two- to threefold increase in the worm's normal (10-day) life span. See H9.
Subjects: Genetics and Genomics.