Fig. 4. Expression of Pou3f3 RNA during jaw development and craniofacial skeletal defects in Pou3f3^-/- mutants. (A-E) In situ hybridization for Pou3f3 on the coronal sections of E10.5 (A,B) and E13.5 (C-E) wild-type heads. B and D are high-magnification views of the boxed areas in A and C, respectively. C and E are from the same head, but C is rostral to E. Arrow in C, mdBA1 expression of Pou3f3. (F-M) Head skeleton of E18.5 wild-type (F,H,J,L) and Pou3f3^-/- (G,I,K,M) mice stained with Alcian Blue (cartilage) and Alizarin Red (bone). H and I are enlargements of the boxed areas in F and G, respectively. Asterisks in I indicate the absence of jugal and squamosal bone in the mutant. (J,K) Otic capsule and middle ear ossicles. Open arrowheads, incus phenotype of the mutant; solid arrowheads, abnormal attachment of stapes and styloid process in the mutant. L and M are the same pictures as H and I, but with individual skeletal elements highlighted by color: yellow, zygomatic process of maxilla; green, jugal; dark green, zygomatic process of squamosal; orange, squamosal; gray, lamina obturans. DE, dentary; FN, frontal bone; IN, incus; JG, jugal; LM, lower molar; LO, lamina obturans; MA, maleus; PA, parietal bone; PS, palatal shelf; rt, retrotympanic process of squamosal bone; SP, styloid process; SQ, squamosal bone; ST, stapes; TO, tongue; UM, upper molar; zpm, zygomatic process of maxilla; zps, zygomatic process of squamosal bone. Scale bars: 0.1 mm in A; 0.5 mm in C,E; 1 mm in F,J.