| description |
Brca1 is required for DNA repair by homologous recombination (HR) and normal embryonic development. Here we report that deletion of the DNA damage responsefactor 53BP1 overcomes embryonic lethality in Brca1-nullizygous mice, and rescues HR deficiency, as measured by hypersensitivity to PARP (polyADPribose polymerase) inhibition. However, Brca1,53BP1 double-deficient cells are hypersensitive to DNA interstrand crosslinks (ICLs), indicating that BRCA1 has an additional role in DNA cross-link repair that is distinct from HR. Disruption of the non-homologous end-joining (NHEJ) factor, Ku, promotes DNA repair in Brca1-deficient cells; however deletion of either Ku or 53BP1 exacerbates genomic instability in cells lacking FANCD2, a mediator of the Fanconi Anemia pathway for ICL repair. Brca1 therefore has two separate roles in ICL repair, whereas FANCD2 provides a key activity that can not be bypassed by ablation of 53BP1 or Ku.Overall design: B cells were stimulated to undergo class switch recombination in vitro. Chromatin from B cells was harvested 72 hours post-stimulation and used for RPA ChIP to study the extent of resection of DNA DSBs. |