Generating human neural diversity with a multiplexed morphogen screen in organoids

Morphogens choreograph the generation of remarkable cellular diversity in the developing nervous system. Differen-tiation of stem cells toward particular neural cell fates in vitro often relies upon combinatorial modulation of these signaling pathways. However, the lack of a systematic approach to understand morphogen-directed differentiation has precluded the generation of many neural cell populations, and knowledge of the general principles of regional specification remain incomplete. Here, we developed an arrayed screen of 14 morphogen modulators in human neu-ral organoids cultured for over 70 days. Leveraging advances in multiplexed RNA sequencing technology and anno-tated single cell references of the human fetal brain we discovered that this screening approach generated consid-erable regional and cell type diversity across the neural axis. By deconvoluting morphogen-cell type relationships, we extracted design principles of brain region specification, including critical morphogen timing windows and combinatorics yielding an array of neurons with distinct neurotransmitter identities. Tuning GABAergic neural sub-type diversity unexpectedly led to the derivation of primate-specific interneurons. Taken together, this serves as a platform towards an in vitro morphogen atlas of human neural cell differentiation that will bring insights into hu-man development, evolution, and disease. single-cell RNA-sequencing of human neural organoids cultured in various conditions and primary human fetal striatum ***Please note that raw data is not provided (for the 'fetal striatum; 21 PCW' sample) due to patient privacy***