Ontogeny of the insulin-like growth factor system (IGF-I, IGF-II, and IGF-1R) in gilthead seabream (Sparus aurata): expression and cellular localization.

There is evidence for the presence of an insulin-like growth factor (IGF) system during fish development. The pattern of gene expression of IGF-I, IGF-II, and their cognate receptors during early development of gilthead seabream (Sparus aurata) was studied by reverse transcription-polymerase chain reaction (RT-PCR). Transcripts for IGF-I, IGF-II, and IGF-1R were detected throughout development in unfertilized eggs, embryos, and larvae, suggesting that these mRNAs are products of both the maternal and the embryonic genomes. Analysis of IGF-1R mRNA in various adult tissues using RT-PCR revealed expression in all tissues studied, with the highest levels in gill cartilage, skin, kidney, heart, pyloric caeca, and brain. The distribution of the two types of IGF-1R and IGF-I in gilthead seabream larvae was studied by immunohistochemistry and found to be tissue-specific and age-dependent. IGF-I and its receptors are widely distributed and appear in various tissues of seabream larvae. IGF-I immunoreactivity was highest in skeletal muscle and pancreas. The general distribution of the two types of IGF receptors in larval tissues appeared similar except for the muscle and the corpus cerebelli, in which IGF-1R was detected only by SpIR6 antisera. Both IGF-I and IGF-II may thus play a role during early development of teleosts, as in other vertebrates.