Epigenetic regulation of genomic imprinting in germline cells and preimplantation embryos

Genomic imprinting is an epigenetic process that distinguishes parental alleles and results in specific expression of paternal and maternal genes. Imprints are acquired in the process of gametogenesis when genome-wide epigenetic reprogramming occurs and are maintained during early embryonic development. Therefore, the recognition and maintenance of imprints are very important in genome-wide reprogramming. In this review, we summarize the progresses of imprints removal in primordial germ cells (PGCs), imprints acquisition in parental PGCs, and imprints maintenance during early embryonic development. We also discuss the functional mechanisms of epigenetic factors which protect imprinted genes from whole genome DNA methylation.