Accumulation of RNA on chromatin disrupts heterochromatic silencing. Schizosaccharomyces pombe

Long non-coding RNAs (lncRNAs) play a conserved role in regulating gene expression, chromatin dynamics and cell differentiation. They serve as a platform for RNA interference (RNAi)-mediated heterochromatin formation or DNA methylation in many eukaryotic organisms. We found in Schizosaccharomyces pombe, that heterochromatin is lost at transcribed regions in absence of RNA degradation, although establishment is not affected. We show that heterochromatic RNAs accumulate on chromatin, form R-loops and need to be degraded by the Ccr4-Not complex or RNAi to maintain heterochromatic silencing. The Ccr4-Not complex is localized to chromatin independently of H3K9me and degrades chromatin associated transcripts, which is required for transcriptional silencing. Overexpression of heterochromatic lncRNA at a heterochromatic locus abolishes silencing of an ade6 reporter in wild type cells. Furthermore, euchromatic lncRNA accumulate on chromatin and this regulates their transcription. Our results demonstrate that chromatin bound RNA interfere with heterochromatin organization and silencing. Overall design: RNA, siRNA, ChIP and RIP sequencing in wild type cells and different mutants of S.pombe