Mammalian RNAi represses pericentromeric lncRNAs to maintain genome stability

Mammalian pericentromeric tandem repeats produce long noncoding RNAs (lncRNAs) that are dysregulated in cancer and linked to genomic instability. Identifying the basic molecular characteristics of these lncRNAs and their regulation is important to understanding their biological function. Here, we determine that the Argonaute (Ago) proteins of the RNA interference (RNAi) pathway directly and uniformly repress bidirectional pericentromeric lncRNAs in a Dicer-dependent manner in mouse embryonic and adult stem cells. Ago-dependent and Dicer-dependent autoregulatory small RNAs were identified within pericentromeric lncRNA degradation intermediates. We develop an RNase H cleavage assay to determine the relative proportions and lengths of the pericentromeric lncRNA targets. We find that 5'-phosphate and non-polyadenylated bidirectional pericentromeric lncRNAs are expressed at similar proportions. These lncRNAs can span up to 9 repeats, with transcription from the reverse strand template yielding the longer products. Using pericentromeric repeat RNA reporters, we determine that Ago represses pericentromeric lncRNAs after S phase transcription. Upon loss of Ago, pericentromeric lncRNA dysregulation results in delayed cell cycle progression, a defective mitotic spindle assembly checkpoint (SAC) and genomic instability. These results show that an evolutionarily conserved Ago activity at pericentromeres contributes to mammalian genome stability.