Atlas of cell types and regulatory elements underlying human facial diversity.

Human genetic diversity generates an astonishing variety of facial shapes, and craniofacial anomalies rank among the most common birth defects. Identifying the cellular mechanisms that mediate the genome's influence on facial variation remains a challenge. Here we created a multimodal facial atlas across embryonic weeks 6-11, providing single-cell transcriptomics, chromatin accessibility and spatial transcriptomics, all at single-cell resolution. We characterized 56 cell states, mapping mesenchymal subtypes and their gene-enhancer cis-regulatory landscapes in space and time. Gene expression associations with facial traits were strongest in early mesenchymal progenitor cells, gradually becoming more region restricted. Autocorrelation analysis revealed patterning genes that define spatial neighborhoods of mesenchyme, potentially explaining trait specificity of their nearby variants. Enhancers of key pathology-related genes were found to be likely vehicles for generating facial variation in modern human populations. One such enhancer, linked to PAX1 expression, appears to be important for normal skeletal development in mice. Finally, facial effects inferred from the genome-wide association study, cell signaling interaction analysis and validation in mice revealed that peripheral nerves fine-tune maxilla shape during embryonic development. Together, these data offer new insights into the mechanisms underlying human phenotypic individuality and yield a multimodal atlas useful for studying craniofacial development and abnormalities.