Noncanonical imprinting: intergenerational epigenetic inheritance mediated by Polycomb complexes

Genomic imprinting is illustrative of intergenerational epigenetic inheritance. The passage of parental genomes into the embryo is accompanied by epigenetic modifications, resulting in imprinted monoallelic gene expression in mammals. Some imprinted genes are regulated by maternal inheritance of H3K27me3, which is termed noncanonical imprinting. Noncanonical imprinting is established by Polycomb repressive complexes during oogenesis and maintained in preimplantation embryos and extraembryonic tissues, including the placenta. Recent studies of noncanonical imprinting have contributed to our understanding of chromatin regulation in oocytes and early embryos, imprinted X-chromosome inactivation, secondary differentially DNA-methylated regions, and the anomalies of cloned mice. Here, I summarize the current knowledge of noncanonical imprinting and remark on analogous mechanisms in invertebrates and plants.

Automated summary

Genomic imprinting is an example of intergenerational epigenetic inheritance. It involves epigenetic modifications during the passage of parental genomes into the embryo, resulting in imprinted monoallelic gene expression in mammals. Recent studies have focused on noncanonical imprinting, which is regulated by maternal inheritance of H3K27me3 and plays a role in chromatin regulation, X-chromosome inactivation, DNA methylation, and cloning anomalies.