[Differential epigenetic marking on imprinted genes and consequences in human diseases]

At the time of fertilisation, the parental genomes have a strikingly different organisation. Sperm DNA is packaged globally with protamines, whereas the oocyte’s genome is wrapped around nucleosomes. The maternal and paternal genomes are functionally different as well, and are both required for normal uterine and postnatal development. The functional requirement of both parental genomes is a consequence of differential epigenetic marking by DNA methylation during oogenesis and spermatogenesis, on a group of genes called imprinted genes. After fertilisation, these parental marks persist throughout development and convey the allelic expression of imprinted genes. Pathological perturbation of methylation imprints, before fertilisation in the germ cells, or during development, gives rise to growth-related syndromes, and is frequently observed in cancer as well. Alteration of imprints is thought to occur early in carcinogenesis and shows similarities with the acquisition of aberrant DNA methylation at tumour suppressor genes. This suggests that similar underlying mechanisms could be involved.