Affiliation:
1. Danish Cancer Institute
2. Copenhagen University Hospital
3. Aarhus University
Abstract
Abstract
Ribosomal DNA (rDNA) encodes the ribosomal RNA genes and represents a genomic region that is intrinsically unstable. Despite decades-long awareness of rDNA instability, the underlying mechanisms and implications for genome integrity remain elusive. Here, we use Bloom Syndrome (BS), a rare genetic disease characterized by DNA repair defects and hyper-unstable rDNA, to investigate the mechanisms leading to rDNA instability. We find that in BLM proficient cells the homologous recombination (HR) pathway in rDNA bear resemblance to that of nuclear chromatin; initiated by resection, RPA loading and BRCA2-dependent RAD51 filament formation. However, we show that BLM deficiency compromise RPA-loading and BRCA1/2 recruitment to rDNA, but intriguingly not RAD51. RAD51 accumulation at rDNA occurs despite depletion of resection nucleases but display increased dependency on BRCA1 in BLM deficient cells. Furthermore, we show that rDNA repair intermediates result in micronuclei formation in the absence of BLM. Our findings suggest that rDNA is permissive to RAD51 loading in the absence of BLM, leading to micronucleation and potentially global genomic instability.
Publisher
Research Square Platform LLC