Correction to: Nature https://doi.org/10.1038/s41586-019-1469-8Published online 07 August 2019; corrected online 03 January 2020

In this Letter, all the left (L) and right (R) labels in the sections should be taken as the proper right and left sides of the embryo, respectively. Samples captured from the two lateral sides of the tissue sections were labelled in reverse during image acquisition, in which the ‘left’ (L) samples should be the right-side samples, and vice versa. The original Letter has not been corrected online.