Expression of common carp growth hormone in the yeast Pichia pastoris and growth stimulation of juvenile tilapia ( Oreochromis niloticus)

Abstract

The cDNA encoding mature growth hormone (GH) was cloned from the pituitary of common carp ( Cyprinus carpio) by RT-PCR. To construct the expression plasmid, the GH cDNA was inserted into the pUC18 plasmid and subsequently subcloned into vector pPICZαA, which contains the promotor from the alcohol oxidase ( AOX1) gene and the α-factor signal peptide sequence. The yeast Pichia pastoris GS115 strain was transformed with the expression plasmid. Transgene expression was observed after screening of the transformants with Zeocin™. Results showed that, with methanol induction, recombinant carp GH (rcGH) had been expressed and exported into the culture medium. The production peaked at 72 h of induction and the optimal pH for expression was 6.0. The yield was 300–400 mg l −1 in shaking-flask fermentation medium, accounting for 34.61% of the total supernatant secreted proteins. rcGH was separated through anion-exchange chromatography. The growth rate of juvenile tilapia ( Oreochromis niloticus) injected with purified rcGH, was found to be 24.5% and 53.1% higher than the control at the dose of 0.10 and 1 μg g −1 body weight week −1 respectively ( P<0.001), while the chemical composition of muscle was not affected significantly by the rcGH treatment. The available production of a large quantity of purified rcGH from this work will strengthen the functional study of rcGH for both theoretical and practical purposes.