Parental imprinting, a memory of the maternal or paternal origin of genes

The fourth lecture dealt with a second important example of mammalian epigenetics: "parental imprinting". Two embryologists, Davor Solter and Azim Surani, have carried out pioneering nuclear transplantation experiments in mice to produce embryos from two genomes of maternal origin (gynogenotes) or two genomes of paternal origin (androgenotes). In both cases, they observed early embryonic lethality, even though all these genomes carry the same genetic information. These results echoed the observations of geneticist Bruce Cattanach, who had noted severe phenotypic damage in mice with "uniparental disomy" - i.e., mice carrying, as a result of chromosomal accidents, a pair of chromosomes from only one parent. Again, it was rapidly established in the 1990s that DNA methylation plays an essential role in the non-equivalence of maternal and paternal genomes. More recently, non-coding RNAs have been implicated in various examples of genetic imprinting as well as in the process of X chromosome inactivation, suggesting that these molecules have a key role in the evolution of monoallelic and epigenetic regulatory mechanisms.