Mammalian ageing is accompanied by accumulation of genomic DNA damage and progressive decline in the ability of tissues to regenerate. DNA damage activates the tumour suppressor p53, which leads to cell-cycle arrest, senescence or apoptosis. The stability and activity of p53 are induced by DNA damage through posttranslational modifications such as phosphorylation of Thr 21 and Ser 23 (refs , , , ). To investigate the roles of DNA damage and p53 in tissue-regenerative capability, two phosphorylation-site mutations (T21D and S23D) were introduced into the endogenous p53 gene in mice, so that the synthesized protein mimics phosphorylated p53. The knock-in mice exhibit constitutive p53 activation and segmental progeria that is correlated with the depletion of adult stem cells in multiple tissues, including bone marrow, brain and testes. Furthermore, a deficiency of Puma, which is required for p53-dependent apoptosis after DNA damage, rescues segmental progeria and prevents the depletion of adult stem cells. These findings suggest a key role of p53-dependent apoptosis in depleting adult stem cells after the accumulation of DNA damage, which leads to a decrease in tissue regeneration.