MAURES, TJ; ROYER, T; DUAN, C: Structure, developmental expression, and physiological regulation of zebrafish insulin-like growth factor binding protein-1

In this study, we have cloned and characterized the full-length insulin-like growth factor binding protein-1 (IGFBP-1) cDNA from zebrafish. The full-length 1032 bp cDNA encodes a protein of 283 amino acids. The 263 residue mature zebrafish IGFBP-1 has a predicted molecular size of 28,223 Da. It is most closely related to mammalian IGFBP-1 among members of the IGFBP family. Its sequence identity to that of bovine, sheep, rat, mouse, and human IGFBP-1 is 42-39%. In order to understand the function of IGFBP-1 in early and adult stages, the developmental and physiological regulation of IGFBP-1 mRNA expression was analyzed. Whole mount in situ hybridization failed to detect IGFBP-1 transcript in embryos of 3-4, 9-12, 14-20 hours post fertilization. After hatching, however, IGFBP-1 mRNA became highly expressed in the liver and some nervous tissues. More sensitive RT-PCR analysis indicated the presence of IGFBP-1 mRNA in early embryos, but the levels were low. In the adult stage, the 1.2 kb IGFBP-1 mRNA was detected in the liver and ovary by Northern blot analysis. The IGFBP-1 mRNA levels, in fasted fish, were dramatically higher compared with the fed, normally growing fish. Re-feeding reduced IGFBP-1 expression to basal levels. Likewise, when fish were subjected to hypoxic conditions, the IGFBP-1 mRNA levels were significantly increased. These data indicate that the structure of IGFBP-1 is conserved in zebrafish, and that IGFBP-1 gene is expressed in a tissue- and developmental stage-specific manner. The expression of IGFBP-1 is greatly increased under various catabolic conditions. These findings are consistent with the idea that IGFBP-1 is a growth inhibitory molecule in fish (Supported by NSF Grant IBN-9728911 and 0110864).