Fig. 4: Melanocyte morphologies, lineage marker expression and cellular interactions in the melanocytic intraepidermal compartment.

a, Surface-rendered melanocytes within the MIS, illustrating variations in dendritic (normal) and rounded (transformed) morphologies. Scale bars, 5 µm. b, A representative field of view showcasing the transition of melanocyte morphology from dendritic-like at the DEJ to compact (bottom) and ultimately rounded during pagetoid spread within the epidermis (top). Scale bars, 10 µm. c–h, Representative examples of pagetoid spread cells showing different expression levels of compact shaped cells expressing PRAME and MART1 (c) and 5hmc, sox10 and MART1 (d). e, Pagetoid shaped melanocyte expressing PRAME and MART1. f, Expression of SOX9 from panel e. g, Dendritic shaped melanocyte expressing PRAME and MART1. h, Expression of SOX10 from panel g. Scale bars, 5 µm. i–n, The images of the MIS. i,k,m, Segmentation masks colored by marker intensity and brightness representing mean expression levels of SOX9, SOX10 and PRAME. The masks in gray denote the positions of keratinocytes; the dashed circles denote IFN-rich domains. The markers are as indicated on each panel. j, l, n: j,l,n, High-resolution immunofluorescence images of representative cells stained with the same markers per row. o–p, Images of the MIS as in i–n, but with colors indicating cells positive for PRAME (magenta) or cells dually positive for SOX9 and SOX10 (green). q,r, Images as in i–p but with magenta denoting cells containing nuclear actin rods. s, Maximum intensity projections of cells in the MIS showing gradations in SOX9 (red) and SOX10 (green) expression; the red arrows denote differentiated MART1⁺SOX10⁺ melanocytes; the green arrows denote MART1⁺SOX9⁺ melanocytic cells that have retained dendritic morphology; the yellow arrows denote MART1⁺ melanocytic cells that coexpress SOX9 and SOX10; the white arrows denote keratinocytes (which are also SOX9⁺). Scale bar, 30 μm. t, Similar data for tumor cells in the VGP regions. Scale bar, 30 μm. u, A magnified view of the cells from s. Scale bar, 10 μm.