DNA methylation: an epigenetic mark of cellular memory

DNA methylation is a stable epigenetic mark that can be inherited through multiple cell divisions. During development and cell differentiation, DNA methylation is dynamic, but some DNA methylation patterns may be retained as a form of epigenetic memory. DNA methylation profiles can be useful for the lineage classification and quality control of stem cells such as embryonic stem cells, induced pluripotent cells and mesenchymal stem cells. During cancer initiation and progression, genome-wide and gene-specific DNA methylation changes occur as a consequence of mutated or deregulated chromatin regulators. Early aberrant DNA methylation states occurring during transformation appear to be retained during tumor evolution. Similarly, DNA methylation differences among different regions of a tumor reflect the history of cancer cells and their response to the tumor microenvironment. Therefore, DNA methylation can be a useful molecular marker for cancer diagnosis and drug treatment. Profiling changes to DNA modification in cells over time may help scientists create personalised cancer treatments. Gene expression can be controlled by the addition of methyl groups to DNA without any change in DNA sequence. This process is vital to healthy cell development, but scientists now know that abnormal DNA methylation plays a role in the progression of diseases like cancer. Joseph Costello at the University of California and Mirang Kim at the Korea Research Institute of Bioscience and Biotechnology reviewed understanding of DNA methylation and showed how cells retain some DNA methylation patterns as a form of memory. This means that the origins of faulty methylation states can be traced in individual tumor cells. Tracking these methylation patterns may help researchers unravel the history of individual tumors, and could inform personalised therapies.