DNA methylation changes are highly orchestrated during mouse embryo development. A cycle of demethylation prior to implantation, followed by a wave of de novo methylation after implantation, establishes embryonic methylation patterns critical for determining somatic DNA methylation patterns.23–26 This phenomenon of epigenetic reprogramming is essential for normal embryonic development, as disruption of the methylation cycle during early development causes neural tube deficits27,28 and studies have further shown that DNA methyltransferase 1 (DNMT1) overexpression results in genomic hypermethylation and embryonic lethality.29,30
