Insulin-like growth factor binding protein-2 (IGFBP-2) in orange-spotted grouper, Epinephelus coioides: Molecular characterization, expression profiles and regulation by 17β-estradiol in ovary

In the present study, a full-length cDNA encoding the insulin-like growth factor binding protein-2 (IGFBP-2) was cloned from the liver of orange-spotted grouper (Epinephelus coioides) by rapid amplification of cDNA ends technique. The IGFBP-2 cDNA sequence was 1413 bp long and had an open reading frame (ORF) of 813 bp encoding a predicted polypeptide of 270 amino acid residues. The deduced amino acid sequence contained a putative signal peptide of 22 amino acid residues resulting in a mature protein of 248 amino acids. Using semi-quantitative RT-PCR, tissue distribution pattern showed that IGFBP-2 mRNA was observed in all regions of brain with high levels, except lower levels in cerebellum and hypothalamus. In peripheral tissues, IGFBP-2 mRNA was most abundant in liver, although relatively high levels were observed in intestine, ovary and pituitary. Low or no IGFBP-2 mRNA expression was observed in other examined tissues. From the multicellular stage to the hatching stage, IGFBP-2 mRNA was expressed consecutively. Furthermore, 1 nM 17β-estradiol could inhibit the ovarian IGFBP-2 mRNA expression significantly in vitro. The mRNA expression and regulation profiles suggest that the IGFBP-2 may play important physiological roles in fish growth and reproduction, as well as cell growth and organ differentiation during the embryonic developmental stages.