Evolution of insulin-like growth factor binding proteins.

In order to understand more about the origins and evolutionary relationships of insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) we have commenced characterization of the IGFBPs in non-mammalian sera. We show by both in vitro labelling with subsequent analytical gel filtration and by ligand blotting that IGFBPs are present in lamprey serum, indicating that the IGFBPs are indeed, very ancient proteins. Furthermore we present evidence that the major serum IGFBP in lamprey is significantly smaller than the high molecular weight IGFBP3 complex in rat serum. In addition, we show that IGFBPs occur widely throughout vertebrates as we detect IGFBPs in ligand blots of serum from marsupials, monotremes, reptiles, birds and turtles.