Epigenetics, the study of the changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself, has taken centre stage in our understanding of gene regulation, cellular differentiation and human disease. The process of adding a methyl group to a DNA molecule (DNA methylation) is one of the most prevalent epigenetic modifications in mammals whereby three major DNA methylation enzymes (DNMT1, DNMT3a and DNMT3b) deposit tens of millions of these "diacritic marks" in the genome creating cell type-specific methylation patterns. Although DNA methylation has been extensively investigated, key mechanisms of these fascinating events remain obscure. The project aims to engineer an advanced cellular system (named liveTAG) that will give a comprehensive view of the roles that the three DNA methyltransferases play in establishing cell-specific genomic methylation patterns and how they govern cell variability and ability to differentiate during mammalian development. The study aims to deepen our understanding of epigenetic regulation in mammalian cells which has important implications in human development and disease.