Structural, gene expression, and functional analysis of the fugu (Takifugu rubripes) insulin-like growth factor binding protein-4 gene

The insulin-like growth factor (IGF) signaling pathway is a conserved pathway that regulates animal development, growth, metabolism, reproduction, and aging. The biological actions of IGFs are modulated by IGF-binding proteins (IGFBPs). Although the structure and function of fish IGFBP-1, -2, -3, and -5 have been elucidated, there is currently no report on the full-length structure of a fish IGFBP-4 nor its biological action. In this study, we cloned and characterized the IGFBP-4 gene from fugu. Sequence comparison, phylogenetic, and synteny analyses indicate that its chromosomal location, gene, and protein structure are similar to its mammalian orthologs. Fugu IGFBP-4 mRNA was easily detectable in all adult tissues examined with the exception of spleen. Older animals tended to have higher levels of IGFBP-4 mRNA in the muscle and eyes compared with younger animals. Starvation resulted in significant increases in IGFBP-4 mRNA abundance in the muscle, liver, gallbladder, and brain. Overexpression of fugu and human IGFBP-4 in zebrafish embryos caused a significant decrease in body size and somite number, suggesting that fugu IGFBP-4 inhibits growth and development, possibly by binding to IGFs and inhibiting their binding to the IGF receptors. These results provide new information about the structural and functional conservation, expression patterns, and physiological regulation of the IGFBP-4 gene in a teleost fish.