Figure 2.

The imprinting cycle of life (based on data from mice, but with similarities in humans). In primordial germ cells (PGCs) in the embryo, DNA methylation is generally erased (solid black line). In the following, de novo methylation signals are established during gametogenesis. Here, a sex-dependent dichotomy can be observed: in the oocytes, general DNA methylation is established after birth (solid red line), whereas in sperm, it occurs soon after demethylation in the embryo and is finished at birth (solid blue line). Establishment of genomically imprinted DMRs can be observed at the same time (dashed lines) but demethylation does not affect imprinted DMRs. Imprinted loci maintain their methylation, whereas non-imprinted loci are rapidly demethylated, either actively in the case of paternal genomes or passively following DNA replication in the case of maternal genomes. It should be noted that the imprinting signature is different for several genes in the placenta and the embryo. (Pictograms have been taken from BioRender.com (accessed on 23 January 2024)).