Résumé
Germ cell differentiation allows the production of mature gametes that are competent for fertilization and that carry genetic but also non-genetically encoded information. DNA methylation is an autonomous epigenetic mark, with intrinsic stability and heritability properties, which allow its transmission from parental gametes to the embryo and the further persistence of sorne parental marks until adulthood. The inheritance of parent-specifie methylation marks fertilization provides the opportunity for differential allelic regulation in the progeny; their maintenance during development is referred to as genomic imprinting. Parent-specific expression of imprinted genes i s regulated by cis regulatory regions called ICRs (lmprinting Control Regions), which carry parent-specifie DNA methylation marks inherited from the gametes. The vast majority of these ICRs are inherited as methylated from the oocyte, and they are systematically coinciding with CpG-rich promoter regions. Through a recent genome-wide screening for the identification of new oocyte-inherited ICRs and therefore new regions of maternal imprinting, we came to the conclusion that genomic imprinting is a very unusual form of regulation of the genome, which affects probably Jess than 30 life-long ICRs. Moreover, white imprinted methylation at ICR was thought to be fully stable throughout life, we provided evidence for the existence of different forms of maternal imprinting. While the classically known JCRs are life-long and ubiquitous, the new ICRs we identified often have stage, tissue or even individual specificities. These findings reveal that certain ICRs can be transiently or sporadically imprinted. We will present a few examples of short and long term influence of maternal ICRs on gene dosage in the progeny.
