We used Lipofectamine2000 (Invitrogen) as the media to transfer the plasmids into OEG. Transfection procedure was performed according to the instructions of manufacturer. Briefly, one day before transfection, cells were plated in growth medium (without antibiotics) in a 24-well plate so that they would be 90%-95% confluent at the time of transfection. Dilute plasmid in 50μL of Opti-MEM I Reduced Serum Medium without serum and mix gently. MixLipofectamine2000 gently before use, then dilute the appropriate amount in 50μL of Opti-MEM I Medium. Mix gently and incubate for 5 min at room temperature. After the 5-min incubation, combine the diluted DNA with the diluted Lipofectamine2000. Mix gently and incubate for 20 min at room temperature to allow the formation of plasmid-Lipofectamine2000 complexes. Add the complexes to each well. Mix gently by rocking the plate back and forth. Incubate the cells at 37oC in a CO2 incubator for 24-48h until they were ready to assay for transgene expression.