(A) The immunofluorescence assay using anti-cytokeratin antibodies showing a positive staining of the 8d-old monolayer of the CPEC (scale bar 10 μm). (B) Transmission electron micrographs of cultured CPE cells demonstrating the ultrastructural features of a polarized epithelial cell monolayer such as a tightly apposed lateral membrane with complex apical junctions organized as a tight junction (TJ) association and complex lateral interdigitations (LI) at the basolateral side (scale bar 0.01 μm, magnification 125.000 ×). (C) Scanning electron micrograph showing a number of processes on the CPEC side which faced apical (upper) chamber (scale bar 2 μm, magnification 6000 ×). (D) Eight-day-old CPE cells grown on laminin-coated filters were stained with primary antibodies against occludin and then with FITC conjugated secondary antibodies. A continuous circumferential distribution of fluorescence consistent with the establishment of TJs in CPEC monolayers is shown. Scale bar 20 μm.