Epigenetic reprogramming, germline and genomic imprinting

The memory of cellular identity is crucial for the correct development of an individual and is maintained throughout life by the epigenome. Chromatin marks, such as DNA methylation and histone modifications, ensure the stability of gene expression programmes over time and through cell division. Loss of these marks can lead to severe pathologies, including cancer and developmental syndromes. However, reprogramming of cellular identity is also a natural phenomenon that occurs early in mammalian development, particularly in the germ line, which enables the production of mature and functional gametes. The germ line transmits genetic and epigenetic information to the next generation, contributing to the survival of the species. Primordial germ cells (PGCs) undergo extensive chromatin remodelling, including global DNA demethylation and erasure of the parental imprints. This review introduces the concept of epigenetic reprogramming, its discovery and key steps, as well as the transcriptional and chromatin changes that accompany germ cell formation in mice. Finally, we discuss the epigenetic mechanisms of genomic imprinting, its discovery, regulation and relevance to human disease.