A promoter trap vector for knocking out bovine myostatin gene with high targeting efficiency

With the development of gene targeting approaches, genomic mutation technologies in livestock animals such as gene trapping, zinc finger nucleases (ZFNs), transcription activator-like effector nucleases, and clustered regularly interspaced short palindromic repeats and their associated systems have been improved. Although ZFNs have been used for gene targeting in many species, the off-target sites are still present. Using gene trapping, the workload of screening of targeted clones was decreased by generating a smaller number of drug-resistant clones. Determining whether the efficiency of gene trapping is lower than that of ZFNs for a specific gene has been challenging. In this study, to knock out the bovine myostatin gene, we constructed a promoter trap vector and compared its efficiency with that of ZFNs. The promoter trap vector contained a green fluorescent protein sequence without the promoter and a neomycin phosphotransferase (neo(R)) cassette driven by the phosphoglycerate kinase promoter. When the trapping vector was inserted downstream of the endogenous promoter, the fluorescent protein gene was expressed. The targeted-positive cell clones were identified based on green fluorescence and G418 double selection, followed by polymerase chain reaction analysis and sequencing. The targeting efficiency reached 5%. Compared with the efficiency of ZFN pairs (5.17 and 2.86%), the promoter trap vector PIII-myostatin could knock out the bovine myostatin gene. Therefore, gene trapping may be an effective tool for genomic modification.