Study on the Cloning, Expression, and Bioactivity of Recombinant Chicken IGF- I

The DNA sequence encoding the chicken's insulin-like growth factor I (IGF- I) was amplified with the reverse transcription polymerase chain reaction (RT-PCR), which was then cloned into vector pMD18-T and sequenced. The sequencing result showed that there was 100% homology among the documented sequences and the sequence reported in this article, which was successfully inserted into the expressing plasmid pRLC and was highly expressed in E.coli. The Tricine-SDS-PAGE result showed that the cloned recombinant protein was expressed in the form of inclusion bodies in the E.coli cell with molecular weight of 7.6 kD and was amount to 23% of the whole protein in the E.coli cell. Western blotting indicated that recombinant protein had the antigenicity of IGF- I. The inclusion bodies were subsequently dissolved in 7 M guanidine chloride and renatured with dilution in refolding buffer containing 0.5 M arginine. To obtain pure protein, the renatured chicken IGF- I was desalting by Hiprep 26/10 and purified by Hiprep Sephacryl S-200 chromatography. The biological activities of IGF- I product were assayed in NIH 3T3 cells and osteoblastic cells of embryonic chicken by using MTT method. The results show that the expressed IGF- I can obviously stimulate NIH3T3 cells and osteoblastic cells to proliferate at the concentration ranging from 100, 200, 400 to 800 ng mL−1, suggesting that the protein has its biological activities.