Nature 461, 654–658 (2009); doi:10.1038/nature08455

In Supplementary Fig. 19a of this Letter, the ‘no treatment’ panels for Stx7 contain incorrect data, owing to an error in image placement during figure preparation. The Supplementary Information to this Corrigendum shows the corrected Supplementary Fig. 19a, and the raw data from which we produced the corrected panels. This error does not affect the description, interpretation or conclusions of the Letter.