Telomeric DNA damage is irreparable and causes persistent DNA-damage-response activation

D’Adda di Fagagna and colleagues observe that, after genotoxic treatment of cells and mice, unrepaired DNA-damage foci and DNA-damage signalling persist at telomeres. They show that introducing the telomeric protein TRF2 near a double-strand break elsewhere on the chromosomes prevents repair. Unrepaired foci are also observed at telomeres of ageing animals, suggesting a role for TRF2 in senescence establishment.