Extraordinary BioMed Seminar: Separating the replicative roles of homologous recombination through the analysis of genomic mutagenesis

Replicative DNA damage bypass mechanisms strongly influence spontaneous mutagenesis.
In cells with defects in homologous recombination (HR), increased mutagenesis encompasses
an elevation in base substitutions, short deletions and large rearrangements. We have recently
shown that translesion DNA synthesis (TLS) is responsible for the increased base substitution
mutagenesis seen in HR deficient cells, implying that HR factors such as BRCA1 and
BRCA2 have a role in template switching (TS), a damage tolerance pathway that provides an
alternative for TLS. Parallel roles of BRCA1 and BRCA2 in DNA double strand break repair
and in the stabilisation of stalled replication forks have made it difficult to assess their
involvement in TS.
We used human and chicken cell line genetics and genomics to study the different roles of
HR in genome stability. Using domain-specific BRCA1 mutants, we provide a functional
separation of the roles of BRCA1 in TS, double strand break repair and replication fork
protection. We correlate the loss of these functions with PARP inhibitor sensitivity, with
relevance to treatment selection based on patterns of mutation in BRCA deficient cancers.