Cloning, characterization, and comparative activity of turbot IGF-I and IGF-II

IGF peptides belong to a complex system that is known to play a major role in the control of growth and development in mammals. Even if studies performed in nonmammalian species tend to demonstrate an important function of these molecules, use of heterologous ligands, especially in fish, partly limit our knowledge of the physiological role(s) of IGFs. We report in this study the cloning, production, and characterization in an evolved fish, the turbot Psetta maxima, of mature IGF-I and IGF-II. The deduced 68-amino-acid IGF-I and 70-amino-acid IGF-II show 75% and 74% sequence identity with their mammalian counterparts, respectively, confirming the high sequence homology observed in other species. The development of a simple and efficient system for the production and purification of both IGF-I and IGF-II in Escherichia coli was used to investigate the in vitro regulation of GH release in the turbot. Our results demonstrated for the first time in a Euteleost species that both peptides specifically inhibited GH release. Both hormones were equally potent in inhibiting GH release from dispersed pituitary cells, with maximal inhibitory effects of 92% and 91% at 1 nM doses after 12 days of culture, respectively. The biologically active recombinant turbot IGFs that we obtained will allow us to further investigate potential and perhaps the specific role(s) of these hormones in turbot as, in contrast with mammals, growth in fish is potentially continued during "adult" life.