Early activation of miR-24 in epidermis restricts epithelial functions. (A) Gross morphology of K5::miR-24 transgenic mice at postnatal day 0, 3, and 10 (P0, P3, and P10). (B) qPCR quantified miR-24 overexpression in transgenic mice skin. (C and D) Hematoxylin-eosin staining of skin (C) and epithelial lining of upper digestive tract (D) sections of P3 mice. Arrowheads indicate basal cells with a flat appearance. Epi, epidermis; Der, dermis; Hf, hair follicles; Adi, adipose tissue; Ms, muscle. (E) Epidermis (black bars; *, P < 0.00001) and digestive epithelia (gray bars; *, P < 0.0001) of miR-24 transgenic mice are thinner than the wt (n = 4 mice for each group). (F) Early expression of miR-24 in stratified epithelia decreases epidermal proliferation, as evaluated by quantification of BrdU-positive cells over the basal layer cells. *, P < 0.001 (n = 4 mice for each group). (G) Basal layer keratinocytes of miR-24 transgenic mice show positive staining for the keratinocyte differentiation marker K10. K10-positive cells are in contact with the basal membrane (red). (H) Coimmunostaining for p63 and K10 (top) and BrdU and K10 (bottom) in P3 mouse epidermis. (I) Histograms show an increased number of BrdU⁺/K10⁺ cells and BrdU⁺/K14⁺ cells in transgenic mouse epidermis after 4 h of BrdU pulse chase. *, P < 0.001 (n = 4 mice for each group). Error bars show means ± SD. Bars: (C) 500 µm; (D and H) 30 µm; (G) 20 µm.