Fig. 3. Microscopic phenotype of Myc KO epidermis. (A,B) Hematoxylin and eosin staining of control (A) or KO (B) epidermis. Note that KO epidermis is thinner and the nuclei smaller, with loss of cellularity in the basal layer (black arrows) and heterogenous mild hyperkeratosis (thickening of squamous layers: black arrowhead). (C,D) Skin sections stained for keratin 10 (green), keratin 5 (red), keratin 1 (green), filaggrin (red), involucrin (red), BrdU (red), Ki67 (green) or for nuclei with DAPI (DNA, either in blue or red) as indicated. Arrows: areas of terminal differentiation in the basal layer. White arrowhead, mild hyperkeratosis. DN, dermal nuclei. Note the smaller size of KO epidermal nuclei. (E,F) Percent of BrdU (E) or Ki67 (F) positive cells with respect to total basal nuclei. Bars are s.e.m. Bar, 20 µm. Ct, control. The dotted line indicates the basal membrane.