Imprinted Igf2r silencing depends on continuous Airn lncRNA expression and is not restricted to a developmental window.

The imprinted Airn macro long non-coding (lnc) RNA is an established example of a cis-silencing lncRNA. Airn expression is necessary to initiate paternal-specific silencing of the Igf2r gene, which is followed by gain of a somatic DNA methylation imprint on the silent Igf2r promoter. However, the developmental requirements for Airn initiation of Igf2r silencing and the role of Airn or DNA methylation in maintaining stable Igf2r repression have not been investigated. Here, we use inducible systems to control Airn expression during mouse embryonic stem cell (ESC) differentiation. By turning Airn expression off during ESC differentiation, we show that continuous Airn expression is needed to maintain Igf2r silencing, but only until the paternal Igf2r promoter is methylated. By conditionally turning Airn expression on, we show that Airn initiation of Igf2r silencing is not limited to one developmental 'window of opportunity' and can be maintained in the absence of DNA methylation. Together, this study shows that Airn expression is both necessary and sufficient to silence Igf2r throughout ESC differentiation and that the somatic methylation imprint, although not required to initiate or maintain silencing, adds a secondary layer of repressive epigenetic information.