The Insulin-like Growth Factor System and Its Biological Actions in Fish

Abstract

The insulin-like growth factor (IGF) system plays an important role in controlling animal development and growth. There are three components to the IGF system: ligands (IGF-I and IGF-II), receptors (type I and type II IGF receptors) and IGF-binding proteins (IGFBPs). These members of the IGF system are expressed differentially and their expression patterns implicate them in critical developmental events. Even though IGFs have been proven essential for normal fetal growth through experiments using IGF “knock-out” mice, the precise role of each member of the IGF system is not fully understood. Recent studies suggest that the IGF system has been highly conserved in teleost fish. This paper provides an overview of what is currently known about the IGF system in teleost fish. Several aspects of the IGF system are discussed, including the structural and functional aspects of fish IGFs, the fish IGF receptors and IGFBPs. The biological actions of fish IGFs are described in reference to their roles in growth, development, reproduction and osmoregulation. Finally, some of the unique advantages of using teleost fish as experimental models for defining the developmental role of the IGF system and the underlying molecular mechanisms are discussed