Note: Funding Information: We thank S. Ladstätter for comments on the manuscript and B. R. Malhotra for assistance with figure preparation. The HCA|Organoid project is funded by the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 874769, coordinator: C.B.). C.B. is supported by an ERC Starting Grant (European Union’s Horizon 2020 research and innovation programme, grant agreement no. 679146). A.R. is supported by the Klarman Cell Observatory and the Howard Hughes Medical Institute. J.A.K. is supported by the Austrian Federal Ministry of Education, Science and Research; the Austrian Academy of Sciences; the Austrian Research Fund (FWF SFB F78 Stem Cell, F 7803-B); and the European Research Council (European Union’s Horizon 2020 research and innovation programme, grant agreements no. 695642 and 693184). This publication is part of the Human Cell Atlas (https://www.humancellatlas.org/publications).