A Human Cell Atlas Of Gene Expression During Development
The emergence and differentiation of cell types during human development is of fundamental interest. We applied an assay for single cell profiling of gene expression based on three-level combinatorial indexing (sci-RNA-seq3) to 121 fetal tissues representing 15 organs, altogether profiling transcription in 4-5 million single cells. From these data, we identify and characterize diverse human cell types and annotate them with respect to marker genes, expression and regulatory modules. We focus our initial analyses of these data on cell types spanning multiple organ systems, e.g. epithelial, endothelial and blood cells, as well as on relating these data to a mouse atlas of organogenesis. Intriguing observations include organ-specific endothelial specialization, potentially novel sites of fetal erythropoiesis, and potentially novel cell types or localizations of known cell types. Together with the accompanying human cell atlas of chromatin accessibility during development, these data comprise a rich resource for the exploration of human biology.