Spontaneous mutation of the lacI transgene in rodents: Absence of species, strain, and insertion‐site influence

Abstract

Comparison of spontaneous mutation spectra derived from different transgenic constructs can provide valuable insights for interpreting the mechanisms of spontaneous mutation. In this study, spontaneous mutation frequencies and spectra of the lacI transgene are compared in the liver of C57BL/6, B6C3F1, and BC-1 mice and F344 rats. Before correction for clonal expansion, the mutant frequency varied from 2.6 +/- 0.45 to 5.0 +/- 2.4 x 10(-5). Correction for potential clonal expansion reduced the range in mutation frequency to between 2.3 +/- 0.45 and 3.5 +/- 2.0 x 10(-5). There is thus no statistical difference in spontaneous mutation frequency between the different strains and species. G:C --> A:T transitions and to a lesser extent, G:C --> T:A transversions dominate the mutational spectra in all of these animals. In three strains of mice, G:C --> A:T transitions account for 50.7-53.3% of mutation, 81.7-83.8% of which involve CpG sites, whereas G:C --> T:A transversions account for 17.8-32.9% of mutations with 43.2-50.0% found at CpG sites. In rats, G:C --> A:T transitions account for 38.0% of the spectra, 70.0% of which involve CpG sites, whereas G:C --> T:A transversions account for 23.0% of the spectra, 70.0% of which involve CpG sites. The distribution of other classes of mutations is also very similar. We conclude that, despite reports about species and strain differences in induced mutation, spontaneous mutations in the lacI transgene appear to be similar, regardless of genomic location, rodent strain, or species. In addition to insights into spontaneous mutation, this study also provides essential data for comparison with and interpretation of induced mutations.

Elevated mutant frequencies and predominance of G:C to A:T transition mutations in Msh6−/− small intestinal epithelium

“…The remainder of the mutation spectrum was comprised primarily of A:T to G:C transitions (11%); various transversions (7%), with G:C to T:A being the most frequent; and +1/71 insertions/deletions (7%), with 71 deletions being the most common. Interestingly, G:C to T:A, and 71, are also the most frequent transversions, and insertions/deletions, respectively, that are seen in MMR-proficient lacI transgenic rodents (Zhang et al, 2001).…”

Theoretical analysis of mutation hotspots and their DNA sequence context specificity

“…The only way to address this problem is to systematically collect and analyze mutation spectra for the same mutational target under different experimental conditions. This approach has been undertaken for lacI and supF (see [8,18,81,155]). …”

Spontaneous Mutagenesis in Rodents: Spontaneous Gene Mutations Identified by Neutral Reporter Genes in gpt Delta Transgenic Mice and Rats

“…43) In sequence analysis of the gpt gene recovered from gpt delta rats, we should note that an unexpected A:T to T:A transversions at position 299 (e.g. nucleotide 299 from the first codon of ATG, in the gpt sequence) was frequently observed.…”

“…Although lower spontaneous gpt MFs than Muta mouse and Big Blue mouse are observed, the characteristic mutation spectra are similar, and the similarity of spontaneous mutation spectra in different tissues and different rodent strains are also observed with the lacI transgene. 42,43) De Boer et al reported the spontaneous lacI mutations for liver, spleen, bladder, stomach, kidney, bone marrow, lung and skin of Big Blue mice. They showed the similarity of the lacI mutational spectra in all tissues.…”