Evaluation of long-term gene expression in mouse liver using PhiC31 integrase and hydrodynamic injection

PhiC31 integrase has the potential to achieve long-term transgene expression because of site-specific and unidirectional recombination. In this study, plasmid DNA (pDNA) encoding Gaussia luciferase (Gluc) cDNA was constructed and the optimal condition for long-term gene expression using phiC31 integrase in mouse liver after hydrodynamic injection was investigated. Gluc is secreted and thus allows quantification of its expression level in blood and easy determination of the expression time-course. Mice were co-transfected with 25 µg donor pDNA (pORF-Gluc/attB) and different amounts of helper pDNA (pCMV-int; from 1 to 50 µg). Serum Gluc expression was evaluated during 120 d. The most highly sustained gene expression was obtained when 10 µg of helper pDNA was co-transfected in ICR and C57BL/6 mice. However, the Gluc expression in C57BL/6 mice was slightly lower and less durable than that in ICR mice. Little hepatic damage caused by phiC31 integrase was observed during 120 d in ICR and C57BL/6 mice.