Duck IL-2 promoter cloning and the effects of methylation status on mRNA levels in immune tissues

Interleukin 2 (IL-2), a cytokine, plays an important role in animal immune systems. To investigate the influences of epigenetic modifications on transcription of the duck IL-2 gene, the promoter region of the duck IL-2 gene was cloned. Then, the DNA methylation status of the IL-2 gene promoter (-1337 bp/-924 bp) in immune tissues of ducks was determined using the Sequenom Mass Array methylation technique, and their corresponding expression levels were determined using real-time PCR. The results showed that 2850 bp of the duck IL-2 gene promoter region were obtained. There was one CpG island (-1231 bp/-902 bp) in which 11 CpG sites were distributed. The CpG1 and CpG2 sites are located between the binding sites of NFAT and AP-1, and they had higher homology methylation patterns in different individuals and tissues. The methylation frequencies of 28.5% CpG sites showed negative correlations with the expression levels of the IL-2 mRNA, whereas 71.5% showed positive correlations. These results indicate that the transcription of duck IL-2 may be distinct from that of mammals. CpG1 (-1284 bp) and CpG2 (-1264 bp) in the duck IL-2 promoter showed a higher homology of methylation patterns, indicating a similar regulatory effect on their gene expression, and these CpG sites may be essential for the regulation of transcription of duck IL-2. The methylation pattern of the IL-2 gene promoter in duck was tissue specific.