Influence of epigenetic changes during oocyte growth on nuclear reprogramming after nuclear transfer

Genomic imprinting is the epigenetic mechanism that distinguishes whether the loci that are inherited from the maternal or paternal genome lead to parent-specific gene expression. The mechanism also regulates development in mammalian embryos. Genomic imprinting is established after implantation according to the specific markers that are imposed on the genome during gametogenesis; the allele-specific gene expression is then maintained throughout embryogenesis. The genomic imprinting markers are erased and renewed on an own-sex basis only in cells that differentiate into germline cells. This report shows that the epigenetic modifications that occur during oogenesis perform the crucial function of establishing the allele-specific expression of imprinted genes, and also suggests that the epigenetic DNA modification is related to the reprogramming and aberrant development seen in manipulated embryos.