Abstract: DNA methylation plays an important role in mammalian fertilization. The chromosome has undergone complex reconstruction and ultimately obtained totipotent during fertilization. Using activation-induced cytidine deaminase protein（AID,also known as AICDA with DNA active demethylation function,as research target,the expression changes of AID and its regulation mechanisms at different development stages of oocyte and in-vitro fertilization（IVF）embryo were detected for exploring the cell reprogramming mechanism. Real-time PCR,BSP（Bisulfite Sequencing PCR）,and immunofluorescence chemistry were used to analyze the effects of DNA methylation on the AID expression during bovine early embryonic development. The results showed that AID gene was regulated by DNA methylation in the bovine early embryonic development. Combining the expression of AID gene in the different tissues and DNA methylation status of its promoter region,the tissue-dependent and differentially methylated region（T-DMR）of AID gene was located at the transcriptional start site -88 bp--431 bp. During the maturing process of bovine oocyte,No. 2 and 3 CpG sites in the T-DMR region were obviously demethylated,whereas the other sites were not changed,and AID gene was correlated with the DNA methylation. At the different stages of early IVF embryo,though the expression of AID gene varied,only No. 2 and 3 CpG sites in the T-DMR region of AID were in the status of demethylation,while other sites were in methylation continuously,the changes of the expression probably was related to the embryonic genome activation. The above results revealed that low methylation of T-DMR in AID gene was correlated with its expression. Immunofluorescence detection discovered that AID proteins were uniformly distributed in the nucleus and cytoplasm from the oocyte maturation stage to morula stage. And a large number of AID protein concentrated in the inner cell mass at the blastocyst stage,which played the important role in the maintenance of pluripotency of the inner cell mass. In summary,accumulated AID during oocyte maturation presents an effect on fertilization,the DNA methylation in the promoter region is closely related to its expression,and the expression of AID gene,after activation of the embryonic genome,may be associated with embryo development.

Key words: AID gene, bovine in vitro fertilization, DNA methylation