IGF3 gene cloning and expression pattern of Protonibea diacanthus

We cloned IGF-Ⅲ gene from Protonibea diacantus by RACE method. The length of cDNA was 1 184 bp. The homologous analysis of deduced protein shows that the identity of IGF-Ⅲ gene and Oreochromis niloticus was 58.0%. Compared with IGF-Ⅱ and two subtypes of IGF-Ⅰof P.diacanthus, the identities were 21.9%, 26.2% and 25.2%, respectively. Phylogenetic tree analysis shows that IGF-Ⅲ tended to cluster with IGF-Ⅱ firstly and then cluster with IGF-Ⅰcomposing IGF family, and finally IGF family clustered in the same branch with Insulin. Tissue distribution shows that IGF-Ⅲ was widely expressed in heart, gonad and brain of P.diacanthus, especially highest in gonad. Quantitative real-time PCR analysis reveals that the expression of IGF-Ⅲ in testis was significantly higher in developing phase than that in the others, showing a significant decline. The expression of IGF-Ⅲ in ovary of maturation phase was also remarkably higher thanthat in other periods. Besides, the expression of IGF-Ⅲ in forebrain, midbrain and hindbrain in female fish in mature phase was higher thanthat in other periods. However, IGF-Ⅲ expression pattern was different in male fish. It is suggested that IGF-Ⅲ might be important for the development of testis and maturation of ovary, and forebrain might involve in the feedback regulation of IGF-Ⅲ expression in gonad.