Nat. Cell Biol. 16, 469–478 (2014); published online 20 April 2014; corrected after print 24 April 2014

In the version of this Article originally published, the bottom panel of Fig. 4b should have read: 'ShhCreER/WT; R26DTA/WT (tamoxifen)'.

In Fig. 7a the three shaded triangles on the left should have been in the sequence: dark, intermediate, light. These errors have now been corrected in the online versions of the Article.