Fig. 3. Snai1^+/- Snai2^-/- palatal shelves display reduced apoptosis and defective periderm migration. (A,B) Scanning electron micrographs of the MEE of control (A) and Snai1^+/- Snai2^-/- mutant (B) embryos at E14.5. Samples were dissected just before palatal shelf fusion, when shelves were in close approximation. Note the appearance of lamellipodia on the MEE of both control and mutant embryos. (C-F) TUNEL staining showing apoptosis along the MES (E) and in the epithelial triangles (C,E) of control embryos at E14.5, whereas mutant embryos (D,F) lack any detectable cell death along the MEE. Arrows, epithelial triangles; arrowheads, MES. (G,H) Keratin 6 immunofluorescence marking periderm cells at the palate fusion point in control embryos at E14.5. Note the concentration of periderm cells in the epithelial triangles in the control embryo, with occasional remaining cells in the MES (G). Mutant palates, in contrast, show the presence of periderm cells at the junction of the adjacent shelves without the formation of epithelial triangles (H). Scale bar: 50 µm.