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Spontaneous mutation spectrum at the lambda cII locus in liver, lung, and spleen tissue of Big Blue® transgenic mice
Author(s) -
Harbach P.R.,
Zimmer D.M.,
Filipunas A.L.,
Mattes W.B.,
Aaron C.S.
Publication year - 1999
Publication title -
environmental and molecular mutagenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1
H-Index - 87
eISSN - 1098-2280
pISSN - 0893-6692
DOI - 10.1002/(sici)1098-2280(1999)33:2<132::aid-em5>3.0.co;2-2
Subject(s) - spleen , biology , transgene , genetically modified mouse , locus (genetics) , lung , genetics , mutation , mutagen , microbiology and biotechnology , gene , immunology , medicine , dna
Big Blue® mice harbor a recoverable transgene in a lambda/LIZ shuttle vector. In the standard assay, in vivo mutations are measured in the bacterial lacI gene using a labor‐intensive color plaque assay. Applying a simpler assay [Jakubczak et al. (1996): Proc Natl Acad Sci USA 93:9073–9078], we measured mutations in the lambda cII gene portion of the transgene. Spontaneous clear plaque mutants were analyzed from liver, lung, and spleen of five untreated mice. Of 314 mutants, 182 (58%) had independent mutations, 74 (23.5%) appeared clonal, and 58 (18.5%) showed no cII mutations. Of 182 independent cII mutations, 156 (85.7%) were base substitutions, 20 (10.9%) were frameshifts, and 6 (3.2%) were multiple substitutions and one deletion. G:C → A:T transitions were the predominant base substitution (78% of these at CpG sites). The major mutation hotspot, a six G run and its 3′ flanking T at bases 179 to 185, comprised 18.7% of the independent mutations. Other hotspots were positions 103, 196, and 212. The in vivo cII spectrum had a significantly higher proportion of G → A and G → T mutations and fewer frameshifts than reported in vitro. The cII and published lacI spectra are similar, though G → A transitions and deletions were fewer in the cII gene. The cI gene was sequenced in 48 mutants with no cII mutations and most had cI mutations: 81.3% base substitutions and 18.7% frameshifts. We conclude that the cII / cI system is insensitive to deletion events, but is useful for detecting point mutations. Environ. Mol. Mutagen. 33:132–143, 1999 © 1999 Wiley‐Liss, Inc.