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 f ull length prepro IGF-I with 161 amino acids: a mature peptide (70 res idues), its signal peptide (44 residues), and a carboxy-terminal E dom ain (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 ma ture peptide were the same. By Northern blot analysis, four different sizes (1, 1.5, 2, and 4.5kb) of IGF-I mRNA were recognized in the live r of juvenile carp. The two smaller species (1kb and 1.5kb) were not d etected in adult carp. The expression of these two species was prefera bly induced by exogenous growth hormone administration in the liver of juvenile carp.