DNA methylation profiling using live-cell imaging

Changes in DNA methylation status at specific gene loci are key epigenetic modifications, which regulate corresponding gene expression patterns. During embryogenesis, de novo methylation takes place in particular genes and this is thought to be associated with cellular differentiation. In contrast, genome-wide changes in DNA methylation are known to occur at particular developmental stages, such as global DNA demethylation during preimplantation development and germ cell formation. These alterations are considered to be the erasure of epigenetic memory or genomic reprogramming. Conventionally, immunostaining using an antibody against 5'-methylcytosine has been performed to analyze global DNA methylation status in situ. We developed a live-cell imaging technique that allows the capture of long-term dynamic changes in DNA methylation three-dimensionally. This technique consists of the construction of a fluorescent probe that can bind specifically to methylated DNA using human methyl-CpG binding domain protein 1, expression of the probe in the cell and prolonged three-dimensional imaging. Using this technique, we were able to observe time-dependent changes in DNA methylation status in living preimplantation mouse embryos. Other groups have used this approach to analyze the drastic differentiation of embryonic stem cells. In this review, I describe the theoretical basis of this imaging and discuss its usefulness and potential for studies on epigenetic regulation, especially in early mammalian development.