Cbx4 partially rescues an epidermal phenotype in p63KO mice. (A and B) Hematoxylin/AP staining (A) and immunodetection of Ki67⁺-proliferating cells (B) in E13.5 ex vivo embryonic skin explants of heterozygous p63^+/−KO mice treated with p63 shRNA– and Cbx4-expressing lentiviruses. Dashed lines separate epidermis and dermis. (C) Cbx4 overexpression in p63-deficient epidermal cells significantly increases epidermal thickness and cell proliferation (mean ± SD). n = 3. (D and E) Quantitative immunofluorescence stainings with anti-K14, anti-K10, and anti-Nefl antibodies show down-regulation of K14/K10 and up-regulation of Nefl (arrows) in the epithelium of p63-deficient skin explants. Cotreatment of the explants with p63 shRNA– and Cbx4-expressing lentiviruses results in up-regulation of K14/K10 expression and down-regulation of Nefl expression in p63-deficient epidermis. Integrin-β4 (Itgb4) expression outlines the basement membrane of the epidermis. DAPI counterstain (blue) shows the nuclei (mean ± SD). n = 3. **, P < 0.01; ***, P < 0.001. (F) Scheme summarizing the p63-/Cbx4-mediated effects on gene repression in the developing epidermis. Bars, 25 µm.