Cloning and Sequence of Two cDNAs Encoding Insulin-like Growth Factors Ⅰ and ⅡGenes(IGF-Ⅰand IGF-Ⅱ) of Zanzibar Tilapia(Oreochromis hornorum) and Their Tissue Distribution
Abstract：Insulin-like growth factors (IGFs) Ⅰ and Ⅱ (IGF-Ⅰ and IGF-Ⅱ) play important roles in fish growth and development. In this study, cDNAs of both IGF subtypes were cloned and sequenced from zanzibar tilapia (Oreochromis hornornum), the expression patterns of the two IGF were detected using semi-quantitive RT-PCR. Total RNAs were isolated from liver of zanzibar tilapia. The cDNAs encoding IGF-Ⅰ and IGF-Ⅱ were amplified by RT-PCR, 3'RACE and 5'RACE. The amplified cDNA fragments were inserted into pMD-T vector. Sequence analysis revealed that the IGF-Ⅰ and IGF-Ⅱconsisted of 1 305 and 1 091 bp, respectively. They all had the characteristic landmarks of IGF, for example, they all possessed signal peptide and B, C, A, D and E domains and six cysteine residues, but their features were distinctly different from each other, the overall deduced amino acid sequence identity between IGF-Ⅰand IGF-Ⅱ was rather low(26%). Under normal physiological conditions, both IGF-Ⅰ and IGF-Ⅱ were present in all tissues examined. IGF-Ⅰwas most highly expressed in liver, muscle and gonad but lowly expressed in kidney. IGF-Ⅱwas most highly expressed in kidney, stomach, intestine, spleen and pituitary, but low in muscle. The mRNA levels of IGF-Ⅱwere higher than that of IGF-Ⅰ in all tissues tested, but significantly difference (P<0.05) only observed in intestine, spleen, stomach, kidney and pituitary. IGF-Ⅰ expressions in females were lower in most tissues examined than those in males except for in spleen, stomach, kidney and pituitary. But significant difference existed in muscle(P<0.05). No significant difference was found in IGF-Ⅱexpression in all the tissues of male and female zanzibar tilapia. This observation can contribute to further investigation of growth regulation of zanzibar tilapia, and the results will give us a better understanding for the physiologyical role of IGFs in fish.
