Molecular cloning and tissue expression of the insulin-like growth factor II prohormone in the bony fish Cottus scorpius

The cDNA encoding pro-IGF-II of an advanced teleost fish, Cottus scorpius ( Scorpaeniformes), the daddy sculpin, was isolated from liver by RT-PCR and molecular cloning. Like other IGFs, the deduced 168 amino acid peptide cont ains B-, C-, A-, D-, and E-domains and six cysteine residues (Cys(B9) Cys(B 21), Cys(A6), Cys(A7), Cys(A11), and Cys(A20)) necessary for the maintenanc e of tertiary structure. At the amino acid level, the sculpin IGF-II prohor mone exhibits 85-92% homology to pro-IGF-II of other bony fish but only 51% homology to human. The mature sculpin IGF-II peptide comprises 70 amino ac ids. Its A-, B-, and D-domains exhibit homologies as high as 91, 91, and 10 0%, respectively, when compared with the other bony fish species studied. T he high sequence homologies may indicate a particular physiological impact of IGF-II in bony fish. RT-PCR followed by Southern blotting revealed an IG F-II mRNA transcript of the expected size in Liver, pyloric and splenic isl ets, stomach, small and large intestine, kidney, gill, testis, ovary, brain , and heart. The local production of IGF-II in many organs indicates that I GF-IT is involved in organ-specific functions in a paracrine/autocrine mann er. Furthermore, the results show that all bony fish organs which have been demonstrated to express IGF-I mRNA also express IGF-II mRNA. (C) 1999 Acad emic Press.