DNA methylation during mouse development is known to be a dynamic process; fertilization involves the removal of paternally contributed DNA, and this loss of DNA methylation continues until the blastocyst stage, when the inner cell mass (ICM) forms (Reik et al). After this stage, embryo implantation occurs alongside global re-methylation of the genome that is believed to contribute to lineage restriction and the loss of cellular potency (Kafri et al and Borgel et al). However, while this model is informative, no base-resolution maps covering stages of mouse development have been constructed to allow for its precise analysis. Now in a report published in Nature from the laboratory of Alexander Meissner at the Broad Institute of MIT and Harvard, USA, researchers have generated such maps, providing provide a genome-scale, base-resolution timeline of DNA methylation where they demonstrate the dynamic nature of this epigenetic mark, before it returns to an expected somatic pattern (Smith and Chan et al).
