Nat. Cell Biol. 16, 268–280 (2014); published online 23 February 2014; corrected after print 26 February 2014

In the version of this Article originally published, the labels of the key in the upper panel of Fig. 7h should have read 'HT29-Vec' (black) and 'HT29-146a' (grey). This error has now been corrected in the online versions of the Article.