Genomic imprinting and cancer: Remembering the parental origin

Genomic imprinting results in only one copy of a diploid pair of alleles being expressed in a parentof-origin-specific manner. The ‘imprint’ encodes a memory of whether a gene came through the maternal or paternal line and contains the information that decides which parental copy will be active or silent. Imprints are established in the developing gametes, passed on to the next generation after fertilization where they are read and maintained in the somatic cells or erased and reset in the germ cells. The components of the ‘memory’ are a combination of epigenetic features such as DNA methylation, post-translational histone modifications and protein/RNA factors that can bind to DNA and label the genes such that a cell's transcription machinery can distinguish between maternal and paternal alleles. Most imprinted genes are associated with sequences that are methylated on only one parental allele, known as differentially methylated regions (DMRs).