A Recql5 mutant enables complex chromosomal engineering of mouse zygotes

Complex chromosomal rearrangements (CCRs) are often observed in clinical samples from patients with cancer and congenital diseases but are difficult to induce experimentally. For generating animal models, these CCRs must be induced as desired, otherwise they cause profound genome instability and/or result in cell death. Here, we report the first success in establishing animal models for CCRs. The disruption of Recql5, which degrades RAD51 during DNA repair, successfully induces CRISPR/Cas9-mediated CCRs, establishing a mouse model containing triple fusion genes and megabase-sized inversions. Notably, some of these structural features of individual chromosomal rearrangements use template switching and microhomology-mediated break-induced replication mechanisms and are reminiscent of the newly described phenomenon "chromoanasynthesis." Whole-genome sequencing analysis revealed that the structural variants in these mice caused only target-specific rearrangements. Thus, these data show that Recql5-deficient mice would be a novel powerful tool for analyzing the pathogenesis of CCRs, particularly chromoanasynthesis, whose underlying mechanisms are poorly understood.