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Figure 2 Postembryonic skin cell lineage relationships are not reflected in UMAP space. (A) UMAP visualization showing distribution of differentiated scale-forming cell (SFC) expressing sp7 and pre-SFC progenitors expressing runx2b. (B) In situ hybridization of sp7 and runx2b shows that a halo of pre-SFC progenitors surround the growing scale (arrows). (C) sp7:nEOS-expressing differentiated SFC (magenta) were labeled by photoconversion on day 1. Over the following 2 d, newly differentiated, un-photoconverted SFC appeared at the scale margin (arrows; n = 5 fish). (D) Schematic representation of differentiated SFC (purple) and the associated halo of pre-SFC (blue). (E) Photoconversion of small groups of SFC in the scale margin and sub-margin; and single-cell photoconversion of focus SFCs (arrows) showed that SFC are progressively displaced toward the scale focus and that SFC in all these regions are capable of cell division (arrows, n ≥ 4 fish for each region tested). Margin SFCs were displaced toward the posterior by newly differentiated, un-photoconverted SFCs (arrowheads). (F) SFCs in UMAP space colored by ‘pseudotime’ rooted in the SFCs. (G) SFCs in UMAP space colored by the ratio of a mesenchymal (migratory) signature to an epithelial signature (Supplementary file 2—Table 3). (H) Schematic representation of epidermis with major substrata. (I) UMAP visualization of wild-type epidermis, subclustered independently of other cell types and displaying expression of the epidermal basal cell marker tp63 (blue) and the periderm marker krt4 (red). (J) The fraction of cells from panel (H) that pass a minimum threshold for expression of tp63, krt4, or both genes. Scale bars, 50 μm (B, C, E); 25 μm, (C, lower).