title: A selectable system for mutation detection in the Big Blue lacI transgenic mouse system: what happens to the mutational spectra over time.
abstract: Transgenic animals offer a powerful tool to study the mechanisms of spontaneous and induced mutagenesis in vivo. Herein we used a test version of a growth selectable assay to obtain spontaneous mutants in a lacI target transgene recovered from lacI transgenic B6C3F1 mice (Big Blue). This selection system may have certain advantages relative to the more established plaque screening system for mutation detection because: (1) the plating density of the phage is up to 60 times higher in the selectable assay, reducing the number of plates needed to be screened for a comparable amount of mutants; and (2) the mutant frequency obtained from the selectable assay is higher compared to the plaque assay, possibly due to a higher sensitivity for weaker mutants. However, the longer incubation time of the growth selectable assay might allow E. coli host derived mutants to appear. To address this issue, we investigated the sequence changes in the amino-terminal domain of the lacI gene of 405 mutants derived from the liver, spleen, brain, germ cells and skin of five untreated 6-week-old mice. The mutant colonies were isolated after 60, 84, 108 and 150 h of incubation under growth selectable conditions. Tissue-specific differences in the mutational pattern obtained after 60 and 84 h disappear after a longer time of incubation, possibly due to an increasing contribution of E. coli derived mutants. The evolving selectable systems offer the potential to increase screening efficiency, but the results suggest caution in interpreting data from this system because repair by E. coli of DNA lesions or mismatched heteroduplexes either originating in mouse in vivo or produced by ex vivo manipulation as well as de novo mutations in E. coli might contribute significantly to the observed mutational spectra at each timepoint.
authors.affiliation: Department of Biochemistry and Molecular Biology, Mayo Clinic/Foundation, Rochester, MN 55905, USA.
authors.forename: A
authors.initials: A
authors.lastname: Knöll
authors.forename: D P
authors.initials: DP
authors.lastname: Jacobson
authors.forename: H
authors.initials: H
authors.lastname: Nishino
authors.forename: P L
authors.initials: PL
authors.lastname: Kretz
authors.forename: J M
authors.initials: JM
authors.lastname: Short
authors.forename: S S
authors.initials: SS
authors.lastname: Sommer
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D010582:Bacteriophage lambda / Q000235:genetics; D001483:Base Sequence; D001921:Brain; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial / Q000235:genetics; D005822:Genetic Vectors / Q000235:genetics; D005854:Germ Cells; D056968:Lac Repressors; D008099:Liver; D051379:Mice; D008822:Mice, Transgenic / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D009928:Organ Specificity; D012097:Repressor Proteins / Q000235:genetics*; D012867:Skin; D013154:Spleen
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D056968:Lac Repressors; C539064:LacI protein, E coli; D012097:Repressor Proteins