ABSTRACT
Genomic imprinting refers to monoallelic gene expression that occurs in a manner that is specific to the parent of origin. The power of the imprinting control region (ICR) to direct imprinting has been demonstrated by experiments in which the ICRs have been removed from known imprinted genes, leading to the loss of the imprinting—that is, to expression from both alleles. The differentially methylated regions (DMR)-swapping experiments mentioned above suggest the presence of an imprinting signal in the DMRs of different imprinted loci. Chromatin modification by covalent post-translational modification of histones also seems to have a role in imprinting. DMRs are sites of differential chromatin structure between the two alleles of an imprinted gene. To answer the questions of how and why imprinting was established, we need to consider the cycle of imprinting changes that occurs during embryogenesis. The chapter discusses some of the basic mechanisms through which epigenetic modifications may contribute to the phenomenon of gene imprinting.
