Antisense Activity across the Promoter is Required for -Mediated Silencing in the Imprinted Cluster.

Macro long non-coding RNAs (lncRNAs) play major roles in gene silencing in inprinted gene clusters. Within the imprinted cluster, the paternally expressed lncRNA downregulates its sense counterpart . To explore the mechanism of action of , we generated two new knock-in alleles to truncate upstream and downstream of the promoter. We show that is essential for methylation of the differentially methylated region (DMR), but higher levels of are required for methylation than are needed for downregulation of . Although is transcribed for over 27 kb, only transcript/transcription across a 2.6 kb region that includes the promoter is necessary for methylation of the DMR. In both mutants, the levels of were extraordinarily high, due at least in part to increased stability, an effect not seen with other imprinted lncRNAs. However, even when levels were greatly raised, remained exclusively -acting. We propose regulates methylation and expression to ensure appropriate levels of expression of the protein coding transcripts and on the paternal chromosome. Thus, mediates paternal gene expression over the entire cluster via a single gene, .