Systematic analysis of mutational spectra associated with DNA repair deficiency in C. elegans

Genome integrity is particularly important in germ cells to faithfully preserve genetic information across generations. As yet little is known about the contribution of various DNA repair pathways to prevent mutagenesis. Using the model we analyse mutational spectra that arise in wild-type and 61 DNA repair and DNA damage response mutants cultivated over multiple generations. Overall, 44% of lines show >2-fold increased mutagenesis with a broad spectrum of mutational outcomes including changes in single or multiple types of base substitutions induced by defects in base excision or nucleotide excision repair, or elevated levels of 50-400 bp deletions in translesion polymerase mutants (pol ζ) and (pol η). Mutational signatures associated with defective homologous recombination fall into two classes: 1) mutants lacking or /RAD51 paralogs show elevated base substitutions, indels and structural variants, while 2) deficiency for MUS-81/MUS81 and SLX-1/SLX1 nucleases, and HIM-6/BLM, HELQ-1/HELQ and RTEL-1/RTEL1 helicases primarily cause structural variants. Genome-wide investigation of mutagenesis patterns identified elevated rates of tandem duplications often associated with inverted repeats in mutants, and a unique pattern of ‘translocation’ events involving homeologous sequences in paralog mutants. ATM DNA damage checkpoint mutants harboured complex structural variants enriched in subtelomeric regions, and chromosome end-to-end fusions. Finally, while inactivation of the -like gene did not affect mutagenesis, combined deficiency displayed increased, locally clustered mutagenesis. In summary, we provide a global view of how DNA repair pathways prevent germ cell mutagenesis.