Molecular cloning and expression of insulin-like growth factor-I (IGF-I) in Eurasian perch (Perca fluviatilis): lack of responsiveness to growth hormone treatment

Summary

The cloning of Eurasian perch (Perca fluviatilis) insulin-like growth factor-I (IGF-I) liver cDNA resulted in the identification of two transcripts of 794 and 713 nucleotides. Whereas the long IGF-Ib isoform consisted of 186 residues, the short IGF-Ia isoform was lacking 27 residues of the E domain due to alternative exon splicing. The long isoform was more abundant than the short isoform in liver, while the expression of both isoforms was rather low in non-hepatic tissues. In order to elucidate the specific endocrine regulation of growth in perch, effects of growth hormone (GH) treatment on weight gain and hepatic IGF-I expression were investigated in juvenile Eurasian perch. Fish injected with Southern black bream (Acanthopagrus butcheri, Perciformes) GH (0.5 μ g/g body weight) grew significantly faster than the saline injected control group, whereas treatment with bovine GH (1.0 μ g/g body weight) gave no growth enhancement. No effects of the GH treatments on hepatic IGF-I mRNA expression were shown by Northern blot analysis. Thus, the impact of GH-IGF-I axis on growth regulation in Eurasian perch remains unclear, but might be affected by IGF-binding proteins (IGFBPs).