21 SITE-SPECIFIC RECOMBINATION USING Dre-RECOMBINASE IN PORCINE CELLS AND EMBRYOS

Site-specific recombinases (SSR), such as Cre and Flp recombinases, which enable DNA excision, insertion, and translocation, have been used for conditional target gene expression in mouse and other vertebrates. In this study, we evaluated another SSR, Dre-recombinase (Dre), which is functionally similar to Cre recombinase in porcine fibroblasts and embryos. For this study, 2 fragment DNA constructs (rox GFP-polyA and rox RFP-polyA) were combined with piggybac transposition expression vector (Kim et al. 2011 J. Vet. Med. Sci.) using a multisite gateway cloning system (MultiSite Gateway® Pro, Invitrogen, Carlsbad, CA, USA). The expression vector carrying rox-flanked green fluorescent protein (GFP) followed by red fluorescent protein (RFP) and transposase were transfected into kidney-derived porcine cells by nucleofection (Neon® Transfection System, Invitrogen). A GFP-expressing cell line, which was not expressing RFP, was established. And then rox-flanked GFP were removed by Dre transfection and RFP was expressed in the kidney cells. At the cellular level, this excision was confirmed by site-specific RT-PCR and sequencing. The rox-flanked GFP cells were reconstructed with enucleated oocytes and then the cloned embryos were cultured in porcine zygote medium-5. Dre was micro-injected into 1 of the 2-cell-stage blastomeres. After 6 days, RFP expression was observed on the part of embryos after microinjection. In conclusion, the data demonstrated that, like other SSR, Dre might be applied in conditional target gene expression for generating porcine biomedical models.