Data are archived at the Salk Institute. We thank P. Adams for discussions and U. Manor and L. Andrade in the Waitt Advanced Biophotonic Core for transmission electron microscopy experiments. J.N. was supported by EMBO (ALTF213-2016) and the Hewitt Foundation. R.R. was supported by the Paul F. Glenn Center for Biology of Aging Research. The Salk Institute Cancer Center Core Grant (P30CA014195), the NIH (R01CA227934, GM087476, R01CA174942), the Donald and Darlene Shiley Chair and the Helmsley, Auen and Highland Street Foundations support J.K.

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Nature thanks M. Narita and the other anonymous reviewer(s) for their contribution to the peer review of this work.