Nat. Cell Biol. 13, 30–39 (2011); published online 12 December 2010; corrected after print 21 December 2010;

In the version of this article initially published online and in print, grant information was missing from the acknowledgements. The acknowledgements have been updated as follows:

“We thank S. Chandra for discussions, and J. Mitchell, A. Roth and I. Kornblum for technical support. This work was supported by the National Institute on Aging (NIH grant RC2AG036614 to T.C.S.), and fellowships from the Human Frontiers Program (LT00527/2006-L to M.S.) and the 'Deutsche Akademie der Naturforscher Leopoldina' (BMBF-LPD 9901/8-161 to J.B.).”