Most biological activities have an epigenetic basis. A given cell has its own epigenetic setup which allows for various biochemical events to proceed. Our major research effort is focused on mechanisms of gene regulation involving genome modifications, e.g. DNA cytosine methylation in mammalian development and human diseases. The key players are the cytosine-modifying enzymes, DNA methyltransferases (DNMTs) and dioxygenases commonly known as TET (Ten-eleven translocation) enzymes. Both DNMT and TET enzymes are essential for animal development and their mutations are widely associated with genetic disorders and cancers. Recent studies from our lab and others have indicated that dynamic DNA modifications are involved in stem cell maintenance, lineage commitment and cell reprogramming etc. While the importance of DNA modifications has long been recognized in biomedical sciences, advance in the understanding of biochemical process in embryo and physiologically relevant tissues is lacking. In addition to the major subject surrounding the mechanisms of DNA methylation and oxidation, we are also extending our research to the study of new types of DNA modifications and investigation of the role of aberrant DNA modifications in tumorigenesis, as well as identification of genetic and epigenetic players for the initiation of mammalian meiosis.