Genome-wide detection of DNA double-stranded breaks induced by engineered nucleases

We describe a robust linear amplification-mediated high-throughput genome-wide translocation sequencing (HTGTS) method that identifies endogenous or ectopic "prey" DNA double-stranded breaks (DSBs) across the human genome based on their translocation to "bait" DSBs generated by engineered nucleases. HTGTS with different Cas9:gRNA or TALEN-nuclease on-target baits revealed off-target hotspots for given nucleases that ranged from few or none to dozens or more, and greatly extended known off-target numbers for certain previously characterized engineered nucleases by more than 10-fold. Beyond various types of nuclease off-target collateral damage, we also identified collateral damage in the form of translocations between bona fide nuclease targets on homologous chromosomes. Based on frequent non-specific DSBs making any given human chromosome an HTGTS hotspot region for bait DSBs within it, we found that HTGTS also reveals wide-spread, low-level DSB-generating activities of engineered nucleases. Finally, HTGTS confirmed that the Cas9D10A paired nickase approach suppresses off-targets genome-wide and suggested other strategies to enhance desired nuclease activities.