Spontaneous occurrence of telomeric DNA damage response in the absence of chromosome fusions

Telomeric DNA is protected by the shelterin complex, whose disruption triggers DNA-damage responses, checkpoint activation and chromosomal fusions. Now analysis of human cell lines reveals a spontaneously occurring intermediate state in which the DNA-damage response is activated at the telomeres without cell cycle arrest or chromosomal fusions, and with TRF2 playing a central role in determining such a state.