Fig 1: Characterization of OAF cells during early IVD formation. A) UMAP visualization of the OAF cluster during human early IVD formation at the Noto, Trans, and NPL stages. B) Representative violin plots showing the expressions of PAX1, PAX9, MKX, COL5A1, SOX9, PDGFRL, TAGLN, FMOD, and BGN during human early IVD formation. C) Representative IHC images of TAGLN (upper) and FMOD (lower) in human axial skeleton sections at the indicated developmental stages. Scale bar, 100 µm. D) UMAP visualization of the OAF cluster during mouse early IVD formation at the Noto, Trans, and NPL stages. E) Representative violin plots showing the expressions of Pax1, Mkx, Col5a1, Sox9, Pdgfrl, and Fmod during mouse early IVD formation. F) Representative IF images of Fmod (left) and Tagln (right) in mouse axial skeleton sections at E14.5. The dotted line indicates the presumptive OAF. The asterisks indicate the presumptive IAF. Triangles indicate NP. VB, vertebral body. Scale bar, 200 µm. G) Dot plot showing the mean expression of selected mechanosensitive ion channel genes in the human OAF along with early IVD formation. Dot size indicates the percentage of cells with detected expression. H) Representative images of lineage tracing in Piezo2-Cre;Ai9 mouse IVDs. Scale bar, 200 µm.