Fig. 4. Freeze-fracture electron microscopy reveals assemblies of TJ fibrils in wild-type and mutant cystic EBs. (A) Low-magnification image of large portions of the plasma membrane of a cystic EB. TJ fibrils are seen arranged both as a continuous belt, separating the apical (am) and the basolateral (lm) membrane domains, and as spatially restricted focal arrays within the basolateral membrane. (B-D) Higher magnification views, showing similar TJ belts (three to five strands thick) in one wild-type (WT1) (B), one heterozygous (+/–) (1;166) (C) and one homozygous (–/–) (3;96) (D) EB clone. Similar results were obtained with other clones (Table 5). (E-G) Higher-magnification views, showing focal arrays of TJ fibrils, which segregate microdomains within the basolateral membrane in wild-type (E), heterozygous (+/–) (F) and homozygous (–/–) (G) EBs. The arrowheads point to microvilli. Scale bars, 0.5 µm (A), 225 nm (B-G).