Processing of double-R-loops in (CAG)·(CTG) and C9orf72 (GGGGCC)·(GGCCCC) repeats causes instability

摘要: R-loops, transcriptionally-induced RNA:DNA hybrids, occurring at repeat tracts (CTG)n, (CAG)n, (CGG)n, (CCG)n and (GAA)n, are associated with diseases including myotonic dystrophy, Huntington's disease, fragile X Friedreich's ataxia. Many of these repeats bidirectionally transcribed, allowing for single- double-R-loop configurations, where either or both DNA strands may be RNA-bound. R-loops can trigger instability (CTG)·(CAG) repeats, but the mechanism this is unclear. We demonstrate R-loop-mediated through processing by HeLa human neuron-like cell extracts. Double-R-loops induced greater than single-R-loops. Pre-treatment RNase H only partially suppressed instability, supporting a model in which directly generate aberrant processing, via slipped-DNA formation upon RNA removal its subsequent processing. Slipped-DNAs were observed to form following from R-loops. Since occur absence replication, R-loop source brain. Double-R-loop was extended expanded C9orf72 (GGGGCC)·(GGCCCC) known cause amyotrophic lateral sclerosis frontotemporal dementia, providing first suggestion become unstable. These findings provide mechanistic basis disease-associated repeats.