Molecular cloning and growth hormone-regulated gene expression of carp insulin-like growth factor-I

Two distinct insulin-like growth factor-I (IGF-I) cDNAs were isolated from a juvenile carp liver cDNA library. Both of the cDNAs encoded a full length prepro IGF-I with 161 amino acids: a mature peptide (70 residues), its signal peptide (44 residues), and a carboxy-terminal E domain (47 residues). The similarity of the two cDNA in the open reading frame was 95.1%. The amino acid sequences of E domain predicted by the two cDNAs were different while those of the signal peptide and the mature peptide were the same. By Northern blot analysis, four different sizes (1, 1.5, 2, and 4.5 kb) of IGF-I mRNA were recognized in the liver of juvenile carp. The two smaller species (1 kb and 1.5 kb) were not detected in adult carp. The expression of these two species was preferably induced by exogenous growth hormone administration in the liver of juvenile carp.