Influence of nucleotide excision repair on N-hydroxy-2-acetylaminofluorene-induced mutagenesis studied in lambda lacZ-transgenic mice.

To study the influence of nucleotide excision repair (NER) on mutagenesis in vivo, ERCC1 +/-, XPA-/-, and wild-type (ERCC1+/+ and XPA+/+, respectively) lambda lacZ-transgenic mice were treated i.p. with N-hydroxy-2-acetylaminofluorene (N-OH-AAF) and lacZ mutant frequencies were determined in liver. No significant effect of the treatment on the mutant frequency in wild-type or ERCC1-heterozygous mice was observed. The liver mutant frequency appeared to be significantly increased in treated XPA-/- mice only. To distinguish N-OH-AAF-induced from spontaneous mutations, lacZ mutants derived from treated XPA-/- mice were subjected to DNA-sequence analysis and the spectrum obtained was compared to that established for lacZ mutants in liver of PBS-treated lambda lacZ-transgenic mice of the parent strain 40.6. The N-OH-AAF-induced mutation spectrum appeared to be significantly different from the spontaneous mutation spectrum: the former consisted of mainly (19/22) single bp substitutions targeted at G, of which the majority (12/19) were G:C-->T:A transversions, suggesting that N-(deoxyguanosin-8-yl)-2-aminofluorene [dG-C8-AF], the major DNA adduct in N-OH-AAF-treated mice, is the premutagenic lesion. After analysis of 21 spontaneous mutants, only ten single bp substitutions targeted at G were found, of which five were G:C-->T:A transversions. This study with XPA-/- lambda lacZ-transgenic mice shows that one of the components of NER, that is, the XPA protein, suppresses mutagenesis in vivo.

UVB-induced mutagenesis in hairless lambda lacZ-transgenic mice.

UVB-induced mutagenesis was studied in hairless 40.6 transgenic mice (MutaMouse), which contain the lambda gt10lacZ shuttle vector as a target for mutagenesis. Mice were exposed at the dorsal side to either single doses of 200, 500, 800, or 1000 J/m2 UVB or to two successive irradiations of either 200 and 800 J/m2 UVB, with intervals of 1, 3, or 5 days, or to 800 and 200 J/m2 UVB with a 5-day interval. At 23 days after the last exposure, lacZ mutant frequencies (MF) were determined in the epidermis. The lacZ MF increased linearly with increasing dose of UVB. The mutagenic effect of two successive irradiations appeared to be additive. The UV-induced mutation spectrum was dominated by G:C --> A:T transitions at dipyrimidine sites. DNA-sequence analysis of spontaneously mutated phages showed a diverse spectrum consisting of insertions, deletions and G:C --> A:T transitions at CpG sites. The results indicate that the hairless lambda lacZ-transgenic mouse is a suitable in vivo model for studying UVB-induced mutations.