Fig. 2

Conserved gene signalling underlies the development of feathers, scutate and reticulate scales. Vibratome sectioning of whole-mount ISH samples was done to examine tissue layer-specific expression of β-cat, Shh and Bmp4 during development of avian epithelial appendages. Sections shown are false coloured, with DAPI in grey and gene expression in pink. Immunoreactivity of PCNA was also examined, with DAPI in blue and PCNA in green. PCNA immunoreactivity revealed columnar cells of the basal epithelium with reduced proliferation compared to surrounding cells during the primary epithelial thickening stage, for feathers, scutate and reticulate scales (A, I, Q) (white arrowheads). β-cat expression was localised to the epithelium during both the primary stage and morphogenesis of chick feather, scutate and reticulate scale development (B, F, J, N, R, V). Similarly, Shh expression was localised to the epithelium, although at the reticulate scale primary epithelial thickening stage, localised expression was not observed (C, G, K, O, S, W). Expression of Bmp4 was mesenchymal during the primary stage and observed in both the epithelium and mesenchyme during morphogenesis (D, H, L, P, T, X). Overall, these results suggest avian appendage development is underpinned by conserved gene signalling. White dashed lines separate the basal epithelium from the mesenchyme. Scale bars are 75 µm in length