(a) Wild-type mice were irradiated with increasing UVB doses, and epidermis was harvested at 24 hours for VDR mRNA levels by RT-PCR, normalized to L19 expression. (b) Epidermal explants from wild-type (WT, •) and VDR^−/− (■) mice were irradiated with 354 J/m² UVB, and assayed at 0, 24 and 48 hours for VDR mRNA levels, normalized to GAPDH expression. (c,d) Cultured keratinocytes from floxed-VDR mice expressing control (•) or cre (■) were irradiated with increasing UVB doses, and assayed for VDR expression by RT-PCR, normalized to GAPDH expression (C) and by Western blotting, with results quantified and normalized to actin (d).

(a,b) After 4000 J/m² UVB, 2 day old wild-type (C57BL/6) and VDR^−/− mouse skin was harvested and stained at varying times with primary anti-CPD antibodies (1:1000, Cosmo Biosciences) and fluorescein-labeled secondary antibodies (a). Mean anti-CPD signal 1 hour post-UV (b). C,D) VDR expression in floxed VDR keratinocytes expressing cre recombinase (cre) or luciferase (con) under K14 promoter control assayed by RT-PCR normalized to L19 expression (c) or Western blotting (d) (Teichert et al., 2011). (eg) Floxed VDR keratinocytes expressing cre or control cells were irradiated with 177 J/m² UVB, and assayed immediately (e) or over time for CPDs (e,f) and 6–4PPs (e,g). (h,i) Epidermal explants from² day old mice with floxed VDR expressed control luciferase (con) or cre under K14 control. Following 354 J/m² UVB, explants were assayed for CPDs (h) and 6–4PPs (i) at 0 or 46 hours. A subset of control (con+HU) and VDR knockout (cre+HU) explants were treated with hydroxyurea before and following UVB (h). Higher UVB dose for explants were needed to generate CPD levels comparable to those in cultured cells, likely due to scattering/reflection in whole epidermis.