GSE128513
The Airn RNA does not require any DNA elements within its locus to silence distant imprinted genes
Long non-coding (lnc) RNAs are numerous and found throughout the mammalian genome, and many are thought to be involved in the regulation of gene expression. However, the majority remain relatively uncharacterised and of uncertain function making the use to model systems to uncover their mode of action valuable. Imprinted lncRNAs target and recruit epigenetic silencing to a cluster of imprinted genes on the same chromosome, making them one of the best characterized lncRNAs to silence distant genes in cis. In this study we examined silencing of the distant imprinted gene Slc22a3 by the lncRNA Airn in the Igf2r imprinted cluster in mouse. Previously we proposed that imprinted lncRNAs may silence distant imprinted genes by disrupting promoter-enhancer interactions by being transcribed through the enhancer, which we called the enhancer interference hypothesis. Here we tested this hypothesis by first using allele-specific chromosome conformation capture (3C) to detect interactions between the Slc22a3 promoter and the locus of the Airn lncRNA that silences it on the paternal chromosome. In agreement with the model we found interactions enriched on the maternal allele, but across the entire Airn gene consistent with multiple enhancer-promoter interactions. Therefore, to further test the enhancer interference hypothesis we devised an approach to delete the entire Airn gene. However, the deletion showed that there are no essential enhancers for Slc22a3 within the Airn gene, strongly indicating that the Airn RNA rather than its transcription is responsible for silencing distant imprinted genes. Therefore we propose an alternative hypothesis whereby the chromosome interactions may initially guide the lncRNA to target imprinted promoters and recruit repressive chromatin, and that these interactions are lost once silencing is established. Overall design: RNA-seq and ChIP-seq from F1 extraembryonic tissues extracted from reciprocal crosses between RSDEL mouse and CAST/EiJ