Expression of recombinant tilapia insulin-like growth factor-I and stimulation of juvenile tilapia growth by injection of recombinant IGFs polypeptides

Mature recombinant tilapia insulin-like growth factor-I (IGF-I) polypeptide was produced in Escherichia coli by cloning the IGF-I B to D domains with glutathione-S-transferase (GST, pGEX-2T vector). The recombinant IGF-I fusion protein, produced following induction of E. coli with IPTG induction and digestion with thrombin, appeared as a major protein band with a molecular mass of 7 kDa. Recombinant tilapia IGF-I ([GSPGIHM]-IGF-I) polypeptide bioactivity, as measured in a homologous [H-3]thymidine incorporation assay assessing concentrations ranging from 0 to 120 nM, was found to significantly stimulate cell uptake of [H-3]thymidine. The stimulatory effect of recombinant tilapia IGF-I polypeptide is suggested to be dose dependent. Recombinant tilapia IGF-I and IGF-ZI polypeptides at doses of 0.1, 0.5, 1 and 2 mu g (g body weight per fish)(-1) were injected into juvenile tilapia once a week. At doses of 2 mu g IGF-I (g body weight per fish)(-1) and doses of 2 mu g IGF-II (g body weight per fish)(-1), there were significant increases (**P < 0.01) from week 5 onwards in both body weight (73% for IGF-I, 72% for IGF-II), weight gain (270% for IGF-I, 260% for IGF-LI), and body length (33% for IGF-I, 34% for IGF-II) relative to a similarly treated GST protein control group and untreated group. (C) 2000 Elsevier Science B.V. All rights reserved.