Mutational signature catalogue (MUSIC) of DNA double-strand break repair

Genome alterations arise from inaccurate DNA repair, accumulating into distinct mutational signatures. Here, we investigate the role of every genomically encoded gene in double-strand break (DSB) repair by generating high-resolution outcome profiles following gene knockouts. Using a CRISPR/Cas9-based, massive-parallel bulk library approach, we construct a comprehensive, user-explorable mutational signature catalogue (MUSIC), mapping the full repertoire of DSB repair factors. Our analysis identifies and validates gene clusters - including nearly all known and several novel genes - linked to non-homologous end-joining, 53BP1 sub-pathways, homology-directed repair, and polymerase Theta (POLQ)-mediated end-joining. By focusing on pathway-specific repair outcomes, we uncover a previously unrecognized role for the WRN helicase in suppressing inverted templated insertions, a poorly understood POLQ-associated mutational signature also found in human disease alleles. Furthermore, in-depth analysis of MUSICs scar features reveals unexpected distinctions among genes within the same pathway, providing mechanistic insight and opening multiple new avenues for investigation into chromosomal break repair.