Fig. 4. Effects of Mi-2ß depletion in the dorsal epidermis. (A-D) Development of the basal and suprabasal layers was examined by immunofluoresence using antibodies to K5, K1, loricrin and keratin 6 (K6). DAPI-stained nuclei are shown in blue. Expression of K5, K1 and loricrin was similar in WT and mutant throughout development (A-C). The K6-positive periderm detected at E16.5 was shed at E18.5 in both WT and mutant (D). From E18.5 through P1, K6 induction was observed in the suprabasal layers of the mutant but not WT skin (D). (E) Skin barrier function was analyzed by a barrier-dependent dye exclusion assay at E19.5. The WT and, for the most part, the mutant dorsal epidermis prevented dye penetration indicating intact barrier function. By contrast, the ventral part of the mutant epidermis was readily penetrated by the dye indicating lack of a barrier. (F) K6 expression (red) is confined to cells that lack Mi-2ß (green). Scale bar: 50 µm.