Molecular cloning, recombinant expression, and growth-promoting effect of mud carp (Cirrhinus molitorella) insulin-like growth factor-I.

A full-length cDNA encoding insulin-like growth factor-I (IGF-I) was cloned from mud carp (Cirrhinus molitorella) liver tissue using reverse transcription polymerase-chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) techniques. The IGF-I precursor cDNA consists of 822 bp in size with a 218 bp 5'-untranslated region and 118 bp 3'-untranslated region. The 486 bp open reading frame encodes a 161 amino acid peptide with a molecular weight of 17.9 kDa. The deduced IGF-I amino acid sequence shared 82.5-97% and 82.5-84% sequence identity with fish and mammalian counterparts, respectively. The mature IGF-I was overexpressed in Escherichia coli, and the expression level of recombinant mcIGF-I reached to 34.1% of the cell total protein. After purification and refolding of recombinant mcIGF-I, growth-promoting effect of recombinant mcIGF-I was investigated, the results showed that the recombinant mcIGF-I significantly enhanced the growth rate of juvenile tilapia. After 6-week treatment, the growth rates of group 1 and 2 were 53 and 67.3% higher than the saline-treated control group. The recombinant mcIGF-I was more effective than recombinant mcGH to enhance the growth rate of juvenile tilapia. The recombinant mcIGF-I-treated fish revealed no significant changes of content of protein, lipid, ash and moisture in muscle.