Epigenome reprogramming in the male and female germ line

Abstract Germ cells reset their epigenome to form a proper epigenetic state for development of the next generation, a process termed epigenome reprogramming. During this process, primordial germ cells (PGCs), the first germ cells and origin of the germ cell lineages, acquire a unique epigenetic profile that includes events such as genome-wide DNA demethylation, large-scale chromatin remodeling, erasure of genomic imprinting, and female X-reactivation. These features crosstalk with each other to regulate the gene expression dynamics of PGCs, and underlie the formation of the totipotent epigenome in the next generation. During the last decade, low-input genomics and in vitro reconstitution of mammalian germ cells have advanced our understanding of epigenome reprogramming. Key findings include details of the dynamics of DNA methylome and histone modifications during PGC development, the formation of sexual dimorphisms in more differentiated germ cells, and the acquisition of a unique epigenome during gametogenesis. Detailed epigenome analyses may also be important for evaluation of germline development in vivo and in vitro.