Reprogramming

Reprogramming refers to erasure and reestablishment of DNA methylation during mammalian development. After fertilization some cells of the newly formed embryo migrate to the germinal ridge and will eventually become the germ cells (sperm and oocytes). Due to the phenomenon of genomic imprinting maternal and paternal genomes are differentially marked and must be properly reprogrammed every time they pass through the germline. Therefore, during the process of gametogenesis the primordial germ cells must have their original biparental DNA methylation patterns erased and re-established based on the sex of the transmitting parent.

After fertilization the paternal and maternal genomes are once again demethylated and remethyated (except for differentially methylated regions associated with imprinted genes). This reprogramming is likely required for totipotency of the newly formed embryo and erasure of acquired epigenetic changes. In vitro manipulation of pre-implantation embryos has been shown to disrupt methlyation patterns at imprinted loci and plays a crucial role in cloned animals.