Correction to: Nature https://doi.org/10.1038/nature19326 Published online 24 August 2016

It was brought to our attention that there are issues with specific images in Fig. 2 and Extended Data Fig. 4 in our paper. With this correction, we would like to address the issues raised and provide further information, including source data. These corrections do not affect our scientific conclusions. Please see the Supplementary information for a detailed listed of changes and the corrected figures.

Supplementary information is available in the online version of this amendment.