Fig. 4. The basement membrane undergoes early and ectopic breakdown in the inner ear of Lrig3 mutant mice. (A,F) Transverse plastic sections through inner ears of E12 Lrig3^+/- (A) and Lrig3^-/- (F) littermates, with magnified views of the boxed areas (A',F'). Dorsal is upwards; lateral is towards the right. In controls, epithelial cells in the fusion plate intercalate to form a single layer of cells (A'), but in mutants, this region is expanded (brackets, F'). Scale bar: 50 µm. (B,C,G,H) Immunofluorescent detection of collagen IV (B,G) and all laminins (C,H) in E12 Lrig3^+/- (B,C) and Lrig3^-/- embryos (G,H) sectioned in the transverse plane. In homozygotes, the basal lamina is disturbed by breaks in the laminin network and ectopic accumulation of collagen IV (arrowheads, G,H). Scale bar: 50 µm. (D,E,I,J) Electron micrographs of the regions indicated in C and H. The basement membrane is continuous in heterozygotes (arrowheads, D,E) but is absent (asterisks, I) or severely disrupted (asterisk, J) in homozygotes. Scale bar: 500 nm.