Fig. 3. Mn1^-/- mutant mice exhibit palatal retardation and failure of palatal shelf elevation. All panels shown are from middle palate regions. (A,B) At E13.5, wild-type (A) and Mn1^-/- homozygous mutant (B) embryos exhibited similar palatal shelf size and shape. (C,D) At E14.5, the wild-type (C) palatal shelves had elevated to the horizontal position above the tongue and initiated fusion by forming the midline epithelial seam, while the Mn1^-/- homozygous mutant (D) palatal shelves were still vertically oriented. (E,F) At E15.5, the wild-type (E) palatal shelves had completed fusion, but the Mn1^-/- homozygous mutant (F) palatal shelves remained vertically oriented. Arrows indicate the first molar tooth germs. p, palatal shelf; t, tongue.