Most biological activities have an epigenetic basis. A given cell has its own epigenetic profile, 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 DNMTs 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, cell reprogramming, tumorigenesis, etc. While the importance of DNA modifications has long been recognized in biomedical sciences, advances in the understanding of biochemical processes in embryos and physiologically relevant tissues are lacking. In addition to studying the mechanisms of DNA methylation and oxidation, we are extending our research to include new types of DNA modifications, organ regeneration through blastocyst complementation, and the mechanisms by which eukaryotes respond to magnetic fields.