Developmental control of imprinted expression by macro non-coding RNAs.

Genomic imprinting is a developmentally regulated epigenetic phenomenon. The majority of imprinted genes only show parent-of-origin specific expression in a subset of tissues or at defined developmental stages. In some cases, imprinted expression is controlled by an imprinted macro non-coding RNA (ncRNA) whose expression pattern and repressive activity does not necessarily correlate with that of the genes whose imprinted expression it controls. This suggests that developmentally regulated factors other than the macro ncRNA are involved in establishing or maintaining imprinted expression. Here, we review how macro ncRNAs control imprinted expression during development and differentiation and consider how this impacts on target choice in epigenetic therapy.