Gene‐ and tissue‐specificity of mutation in Big Blue® rats treated with the hepatocarcinogen <i>N</i>‐hydroxy‐2‐acetylaminofluorene†

<jats:title>Abstract</jats:title><jats:p>In a previous study, we found that treating transgenic Big Blue® rats with the hepatocarcinogen <jats:italic>N</jats:italic>‐hydroxy‐2‐acetylaminofluorene (<jats:italic>N</jats:italic>‐OH‐AAF) produced the same major DNA adduct in the target liver and the nontarget spleen lymphocytes and bone marrow cells, induced <jats:italic>lacI</jats:italic> mutants in the liver, and induced much lower frequencies of <jats:italic>lacI</jats:italic> and <jats:italic>hprt</jats:italic> mutants in spleen lymphocytes. In the present study, sequence analysis was conducted on <jats:italic>lacI</jats:italic> DNA and <jats:italic>hprt</jats:italic> cDNA from the mutants, to determine the mutational specificity of <jats:italic>N</jats:italic>‐OH‐AAF in the rat. All the mutation spectra from <jats:italic>N</jats:italic>‐OH‐AAF–treated rats differed significantly from corresponding mutation profiles from untreated animals (<jats:italic>P</jats:italic> = 0.02 to <jats:italic>P</jats:italic> < 0.0001). Although there were similarities among the mutational patterns derived from <jats:italic>N</jats:italic>‐OH‐AAF–treated rats (e.g., G:C → T:A transversion was the most common mutation in all mutation sets), there were significant differences in the patterns of basepair substitution and frameshift mutation between the liver and spleen lymphocyte <jats:italic>lacI</jats:italic> mutants (<jats:italic>P</jats:italic> = 0.02) and between the spleen lymphocyte <jats:italic>lacI</jats:italic> and <jats:italic>hprt</jats:italic> mutants (<jats:italic>P</jats:italic> = 0.04). Also, multiplex PCR analysis of genomic DNA from the <jats:italic>hprt</jats:italic> mutants indicated that 12% of mutants from treated rats had major deletions in the <jats:italic>hprt</jats:italic> gene; no corresponding incidence of large deletions was evident among <jats:italic>lacI</jats:italic> mutations. All the mutation profiles reflect the general mutational specificity of the major DNA adduct formed by <jats:italic>N</jats:italic>‐OH‐AAF. The differences between <jats:italic>N</jats:italic>‐OH‐AAF mutation in the endogenous gene and transgene can be partially explained by the structures of the two genes. The tissue‐specificity of the mutation spectra may contribute to targeting tumor formation to the liver. Environ. Mol. Mutagen. 37:203–214, 2001. Published 2001 Wiley‐Liss, Inc.</jats:p>