Fig. 4: Epidermal BMP signalling activates during rete ridge formation and maturation.
From: Rete ridges form via evolutionarily distinct mechanisms in mammalian skin
a, Representative immunostains from the basal side of epidermal whole mounts from P3 (n = 3) and adult (n = 2) pig skin stained for ITGA6 and KRT15, showing the topography of rete ridge formation. b, Rete ridge formation establishes an epidermal–dermal signalling niche within the dermal pocket. Representative frame of epidermal–dermal regions from porcine P3 and P10 stereo-seq, visualizing Leiden clusters comprising epidermal and dermal cell lineages, is shown. c, BMP signalling is activated in basal cells during rete ridge formation and maturation. UMAPs depicting integrated postnatal interfollicular epidermis keratinocytes from P3, P10 and 6 mo pig scRNA-seq, coloured by cluster (top left) or age (top right) and with visualization of expression of KRT15, BMP7 and SMAD1 (bottom). The dashed navy polygon outlines the basal cluster 1. d, Predicted epidermal–dermal BMP signalling interactions between epidermal keratinocytes, papillary fibroblasts (Pap. fibro.) and vascular/pericyte clusters during rete ridge formation, represented spatially at P3 and P10 from stereo-seq Spatial CellChat (top row) and as CirclePlots for predicted signalling interactions from P3 and P10 scRNA-seq CellChat (bottom row). The dashed line approximates the epidermal–dermal junction traced from the stereo-seq Leiden-clustered image mask (Supplementary Fig. 8a). e, Epidermal BMP signalling activates during rete ridge formation. UMAP depicting pseudotime trajectory from non-dividing basal to differentiated keratinocyte states from integrated P3, P10 and 6 mo pig interfollicular epidermis scRNA-seq, and pseudotime trajectories for expression of BMP signalling ligands, receptors and downstream elements visualized as a LinePlot (middle). Representative immunostains of P3 (n = 3) and adult (n = 2) pig skin epidermal whole mounts for SMAD1 (bottom). Dashed polygons indicate inter-ridge domains. Div., dividing; IFE, interfollicular epidermis; krtno, keratinocyte; pap. fibro., papillary fibroblasts. Scale bars, 100 μm (a, e), 25 μm (b). Illustrations in a–e were created using BioRender. Thompson, S. (2026) https://BioRender.com/8rd8cz9.
