Spatiotemporal cell landscape of human embryonic tooth development

Understanding the cellular composition and trajectory of human tooth development is valuable for dentistry and stem cell engineering research. Previous single-cell studies have focused on mature human tooth and developing mice tooth, but cell landscape on human embryonic dental development is still lacking. We collected tooth germ tissues from aborted fetus (17-24 week) for single cell RNA sequence and spatial transcriptome. We classified all cells into seven subclusters of epithelium, seven clusters of mesenchyme and other cell types like Schwann cell precursor and pericyte. For epithelium, the Stratum intermedium branch and the ameloblast branch diverged from a same set of KRT15+-HOPX+-ALCAM+ epithelial stem cell lineage, but the spatial distribution of two branches were not clearly distinct. This trajectory received spatially adjacent regulation signals from mesenchyme and pericyte, including JAG1 and APP. The differentiation of pulp cell and pre-odontoblast showed four waves of temporally distinct gene expression, which involved regulation networks of LHX9, DLX5 and SP7 and were regulated by upstream ligands like BMP family. Taken together, we provided a reference landscape for the research on human early tooth development, covering different spatial structures and developmental periods.