TASI, T.; MAURES, T.*; FUNKENSTEIN, B.; DUAN, C.: MOLECULAR CLONING AND EXPRESSION OF INSULIN-LIKE GROWTH FACTOR BINDING PROTEIN-2 IN THE GILTHEAD SEABREAM, SPARUS AURATA

The insulin-like growth factors (IGFs) in extracellular fluids are bound to several high-affinity binding proteins (IGFBPs). The circulating IGF/IGFBP complexes prolong the half-lives of IGFs and buffer the acute hypoglycemic effects of IGFs. Locally expressed IGFBPs may also provide a means of localizing IGFs in defined areas and may alter IGF bioactivity by modulating the ligand receptor interaction. In this paper, we report the cloning of an IGFBP cDNA from the gilthead seabream, Sparus aurata. The cDNA encodes a protein of 285 amino acids. The primary structure of this protein is 43~49% identical to that of zebrafish, chicken, rat, mouse, and human. The sequence identity of seabream IGFBP-2 with other human IGFBPs ranges from 28-34%. Northern blot analysis revealed that the seabream IGFBP-2 transcript is approximately 1.8 kb and is highly expressed in the liver. Analysis of IGFBP-2 mRNA in various adult tissues using RT-PCR revealed its expression in all tissues studied, with the highest levels in liver, skin, gonad and pyloric caeca. The hepatic mRNA levels of IGFBP-2 were greatly reduced in growth hormone-treated animals. This data is in agreement with the role of IGFBP-2 function as a negative growth regulator in the growth hormone-IGF-I axis. Transcripts for IGFBP2 were detected throughout early development in unfertilized eggs, embryos and larvae, with highest levels observed on days 3-6 after hatching, suggesting that this mRNA is the product of both the maternal and embryonic genomes. These data suggest that IGFBP-2 is expressed from the earliest stages of development and may play an important role in regulating growth and development in fish (Supported by BARD Grant IS-2769096R and NSF Grant IBN-9728911).