The Methylation Level of CMV in Fibroblasts of Transgenic Pigs

To investigate the relationship between the expression levels of exogenous gene and methylation level of promoter in cells derived from transgenic pigs,the EGFP fluorescence of the fifth,10thand15 thgeneration fibroblast of EGFP transgenic pigs were detected by flow cytometry,and the methylation status of a 560-bp region of the CMV promoter containing one Cp G island including 30 Cp G sites were examined by bisulfite sequencing method. The mean fluorescence intensity declined from the fifth generation of transgenic pig cells to the 10 th generation cells,however,it increased to the level comparable to the fifth generation of cells from the 10 thto 15thcells. The methylation level of the fifth,10 thand 15thgeneration cells of the CMV promoter were 3. 64% ± 1. 25,2. 97% ± 1. 03 and 1. 65% ± 0. 74,respectively. The difference of methylation level among different generation of transgenic cells was insignificant,which indicated that the expression level of exogenous gene EGFP was not closely correlated to the methylation level on CMV promoter.