Genomic imprinting in human placentation

Abstract

Genomic imprinting (GI) is an epigenetic phenomenon that describes parent-of-origin patterns of monoallelic gene expression reported in mammals. 1 This differential gene expression is initiated within the germline when discrete regions of the genome acquire DNA methylation in one germline but not the other. These differentially methylated regions (DMRs), present within most imprinted loci, are key to establishing and, in some cases, maintaining imprinted gene expression (Figure 1). The difficulty in producing parthenogenetic embryos is due to the fact that mammals must have both male and female GI-bearing genomes in order to develop normally. 2 In primordial germ cells, which differentiate into the germ cells that produce the next generation, most of the memory of the epigenome from both parents, including GI, is erased. A new methylated GI is then established in DMRs in the premeiotic spermatogonia of

Human promoter CpG islands contain primate-specific repeats, cluster and resist reprogramming

“…Transcription of imprinted genes in a dose-dependent manner is required for normal development in mammals, yet generally not required after birth. For example, many imprinted genes are only expressed in the placenta but monoallelic ICR methylation persists for the lifetime of the individual ( 5 ). From this, we reasoned that CGI methylation akin to ICR methylation may occur on non-imprinted sequences, initiated as de novo methylation at some developmental stage post-fertilization, and thereafter maintained by DNMT1.…”