(A and B) WMISH with Ctnnb1 in C. niloticus and P. vitticepsembryos at various developmental stages. Arrowheads indicate the initiation sites of scale tracts and arrows indicate the directions of scale tracts. Colors correspond to different tracts schematically represented in the right panels (dots, initiation sites; arrows, directions of development). (C) WMISH with Shh in P. guttatus embryos at various developmental stages. Arrowheads with white borders indicate tract initiation sites, and arrowheads with black borders indicate the boundaries of Shh expression at different developmental stages, showing the different anteroposterior (a/p) and ventrodorsal (v/d) gradients (see schematic in the right panel).

Anatomical placodes in C. niloticus (left panels), P.vitticeps (middle panels), and P. guttatus (right panels) embryos. For each species, the whole-embryo WMISH with Sonic hedgehog (Shh) is shown (left panel) as well as, from top to bottom, high magnification of H&E-stained placode sections (white arrowheads indicate placode columnar cells), immunohistochemistry with PCNA (proliferation marker; epidermal-dermal junction indicated by dashed white lines), and parasagittal cryosections of placodes after Shh or β-catenin (Ctnnb1) WMISH. Bmp4 is also shown for lizard. Red double-headed arrows indicate the body region processed for sectioning.

(A) Hematoxylin and eosin (H&E) staining of skin sections from different body regions (indicated with red arrows on the top insets with lateral views of corresponding embryos) of C. niloticus (crocodile; top row), P.vitticeps (lizard; two middle rows), and P. guttatus (snake; bottom row) embryos at various developmental stages [indicated as embryonic days (E) after oviposition]. White arrowheads indicate the anatomical placode. Scale bars, 100 μm.