Figure 1.

Somatic maintenance of oocyte-derived DNA-methylation and H3 lysine-27 tri-methylation (H3K27me3) imprints. (A) At most maternal ‘imprinting control regions (ICRs)’, the differential DNA methylation state is maintained in all somatic lineages (‘Constitutive’). At some, however, it persists during extra-embryonic development only and is lost in the embryo proper (‘Placental’). At a few differentially methylated regions (DMRs), the differential methylation and expression status is short-lived and lost in both the embryo and the placenta (‘Transient’). (B) Oocyte-derived H3K27me3 imprints give rise to a paternal allele-biased gene expression that is labile and is lost before implantation at most loci (‘Transient’). At only a handful of genes, the allelic expression persists in the trophoblast (‘Placental’), through somatic acquisition of repressive DNA methylation on the maternal allele. Figure 1 Figure 2 Figure 3 were created using Biorender.com.