Figure 3.

Figure 3. Evidence for epidermal and dermal contributions to scale plate ECM.

(A) Simplified vertebrate phylogeny with schematic depictions of calcified appendages. Phylogeny based on Near et al., 2012; Betancur-R et al., 2013; schematics drawn after (Sire et al., 2009). (B) Dotplot visualization of transcripts encoding enamel matrix proteins (EMPs), fish-specific secretory calcium-binding phosphoprotein (SCPP) tandem duplicates, non-collagen matrix proteins associated with bone and dentin, collagen associated with cartilage and transcription factors that regulate osteoblast and ameloblast differentiation. (C) UMAP visualization of epidermal basal cells showing distribution of transcripts encoding EMPs. (D) Optical sections of growing scale in live animals showing the relative position of calcified matrix dyed with Alizarin Red S (ARS) or Calcein, and dermal scale-forming cell (SFC) visualized with sp7:EGFP transgene and epidermis visualized with krtt1c19e:palm-tgTomato transgene. (E) In situ hybridization of ambn, encoding the EMP Ameloblastin. Arrows point to the calcified scale plate. (F) Schematic representation of epidermal ambn expressing cells (blue), the calcified scale plate (magenta), dermal SFC (green), and epidermis (yellow). (G) UMAP visualization of dermal SFC and pre-SFC. (H) Position of SFC sub-types within a scale inferred from in situ hybridization assays (Figure 2—figure supplement 1). (I) UMAP visualization of transcripts encoding non-collagen matrix proteins associated with bone (spp1, chad), enamel (enam), and cartilage (col10a1a). Scale bar, 10 μm.