Single-Cell Chromatin Accessibility Maps Reveal the Regulatory Programs Driving Early Mouse Organogenesis

During early mouse embryonic development, pluripotent cells rapidly divide and diversify to construct the developing foetus, yet the underlying regulatory programs that define the cell repertoire for each organ remain ill-defined. To delineate comprehensive chromatin landscapes of mammalian lineages during early organogenesis, we mapped chromatin accessibility in 19,453 single nuclei from mouse embryos collected at 8.25 days post-fertilisation. Identification of cell type-specific regions of open chromatin pinpointed known regulatory regions and two new TAL1-bound endothelial enhancers, which we validated using transgenic mouse assays. Integrated gene expression and transcription factor motif enrichment analyses highlighted known and previously unrecognised cell type-specific transcriptional regulators. Subsequent in vivo experiments in zebrafish revealed a powerful role for the ETS transcription factor FEV in endothelial identity. Concerted in vivo validation experiments in mouse and zebrafish thus illustrate how single-cell open chromatin maps, representative of a mammalian embryo, provide access to the regulatory blueprint for mammalian organogenesis. Overall design: 10 mouse embryos were processed using single-nucleus ATAC-seq protocol (Preissl et al., 2018).