Cell proliferation and nuclear abnormalities are increased and apoptosis is decreased in the epidermis of the p53 null mouse after topical application of benzo[ a ]pyrene

. Cell proliferation and cell death in mouse epidermis are altered by topical application of benzo[ a ]pyrene (BaP), a procarcinogen, which yields metabolites that can form DNA adducts. The mitotic rate, nuclear abnormalities, labelling index, grain density, necrosis and apoptosis were compared in the epidermis of TSG‐ p53 null ( p53 ‐/‐ ) and C57BL wild‐type (wt) mice after weekly treatments with BaP to determine whether the absence of the p53 gene altered cytokinetic responses to DNA damaging agents in vivo . Acetone alone or 64 μg BaP in 50 μl acetone was applied to the clipped dorsum of mice once, or in four consecutive weekly treatments. Indices of cell proliferation and cell death were the same in both wt and p53 ‐/‐ mice treated only with acetone. One application of BaP depressed mitosis and slowed the rate of DNA synthesis in both genotypes. After four applications of BaP the number of keratinocytes in S phase increased substantially, while there was no further slowing in the rate of S phase in the wt and p53 ‐/‐ mice. Cell proliferation rates and numbers of cells with nuclear abnormalities were higher and there were fewer apoptotic cells and apoptotic bodies in the p53 ‐/‐ mice than in the wt mice. Numbers of ‘sunburn’cells were similar in both types.