Figure 3
From: Genomic imprinting mechanisms in embryonic and extraembryonic mouse tissues
A summary of published work on imprinted macro ncRNA function in the embryo and in extraembryonic tissues. Genes showing imprinted expression in embryo/adult tissues tend to be close to the ICE that contains the macro ncRNA promoter. DNA methylation is important to maintain imprinted expression in the embryo. In extraembryonic tissues, genes located further away from the ICE/ncRNA promoter will show imprinted expression. DNA methylation may not be required to maintain imprinted expression of genes showing extraembryonic-specific imprinted expression, instead repressive chromatin modifications such as H3K27me3, H2AK119u1 and H3K9me2 that are deposited by polycomb complexes (PRC) and G9A are required to maintain imprinted expression. The macro ncRNA is implicated in recruiting these repressive complexes to extraembryonic-specific imprinted genes. The ncRNA forms a cloud that is larger in extraembryonic tissues and often covers the genes that are silenced (dotted blue line). ICE, imprint control element; M, DNA methylation; and E, enhancer.
