Insulin, insulin-like growth factor-I (IGF-I) and glucagon: the evolution of their receptors

Insulin and glucagon, two of the most studied pancreatic hormones bind to s pecific membrane receptors to exert their biological actions. Insulin-like growth factors IGF-I and IGF-II are structurally related to insulin, althou gh they are expressed ubiquitously. The biological functions of the IGFs ar e mediated by different transmembrane receptors, which includes the insulin , IGF-I. and IGF-II receptors. The interaction of insulin, insulin related peptides and glucagon with the corresponding receptors has been studied ext ensively in mammals and continues to be so. At the same time, research on e ctothermic animals has made enormous progress in the recent years. This pap er summarizes current knowledge on insulin, IGF-I and glucagon receptors, f rom a comparative point of view with special attention to non-mammalian ver tebrates. The review covers adult and mostly typical target tissues, and wi th very few exceptions, developmental aspects are not considered. Binding c haracteristics, tissue distribution and structure of insulin and IGF-I rece ptors will be considered first, because both ligands and receptors are stru cturally related and have overlapping functions. These sections will be fol lowed by similar distribution of information on glucagon receptors. Readers interested in either structure or functions of insulin, IGFs and glucagon in nonmammalian vertebrates are referred to other reviews (Mommsen TP, Plis etskaya EM. Insulin in fishes and agnathans: history, structure and metabol ic regulation. Rev Aquat Sci 1991;4:225-259; Mommsen TP, Plisetskaya EM. Me tabolic and endocrine functions of glucagon-like peptides: evolutionary and biochemical perspectives. Fish Physiol Biochem 1993;11:429-438; Duguay SJ, Mommsen TP. Molecular aspects of pancreatic peptides. In. Sherwood NM, Hew CL, editors, Fish Physiology. vol 13. 1994:225-271; Plisetskaya EM, Mommse n TP. Glucagon and glucagon-like peptides in fishes. Int Rev Citol 1996;168 :187-257,), (C) 1999 Elsevier Science Inc. All rights reserved.