Mutational consequences of ERCC1-deficiency in adult mouse stem cells

Mutagenic processes continuously challenge the genomic integrity of cells, resulting in a gradual accumulation of somatic mutations during life. This accumulation of mutations is associated with the onset of age-associated disease, including cancer. Mutations acquired in the genomes of long-lived adult stem cells (ASCs) are believed to have the largest impact on tissue function, as these mutations are propagated to all progeny cells. We found that ASCs of different organs maintain a remarkable stable genome throughout life, likely reflecting a substantial activity of DNA repair in these cells. Nonetheless, the effects of specific DNA repair activity on the genome-wide mutation patterns in ASCs have not yet been systematically established. Here, we characterized genome-wide mutation profiles of single ASCs from ERCC1-deficient mice. ERCC1 plays a role in multiple DNA repair processes, including nucleotide excision repair and interstrand crosslink repair. ERCC1-deficient stem cells of the liver, an organ that displays severe pathology in this mouse model, show increased mutation load compared to wild-type liver stem cells (~ two-fold increase genome-wide). In contrast, mutant and wild-type stem cells of the small intestine, an organ that is hardly affected in this mouse model, show comparable mutation numbers. In-depth mutational analyses revealed that liver stem cells of ERCC1-deficient mice show a different mutation spectrum, which is among others characterized by T:A>A:T changes. Our approach allows us to establish the genome-wide effects of DNA repair activity in ASCs and to connect DNA repair deficiency to disease phenotype.