A novel germline mutation in Big Blue® mice

Abstract

The Big Blue lacI mutation detection assay is well validated and has permitted detailed analysis of spontaneous mutations in individual tissues over the lifespan of the mouse. In a recent assay of spontaneous mutations, a novel lacI mutation (C354T) recurred in six of seven mutants with a second mutation. The frequency of spontaneous doublets (mutants with two nontandem mutations) was elevated 2.7-fold over that previously reported (Hill KA et al., [2004b]: Mutat Res 554:223-240) for normal tissues (6.3 x 10(-7) herein vs. 2.36 x 10(-7)). The average spacing between mutations in the doublets (237 bp) was greater than previously reported for spontaneous doublets. The frequency of C354T as a "hitchhiker" mutation in doublets was consistent with a germline mutation in one of 38 mutation targets in the Big Blue mouse genome. C354T is a missense mutation at a CpG dinucleotide producing a conservative amino acid change (Ala109Val) and a very light blue mutant phenotype. Mutant phenotypes of doublets with C354T were typical of the second mutation. C354T was observed in mutants from five tissues of five Big Blue mice. A bidirectional-PCR amplification of specific alleles (Bi-PASA) assay detected C354T in genomic DNA from multiple tissues of five Big Blue mice. These observations are consistent with a novel lacI C354T germline mutation in Big Blue mice that introduces a significant artifact in the analysis of spontaneous mutations. This finding reiterates the importance of identifying all mutations and examining new mutations in the context of our increasingly detailed knowledge of features of spontaneous murine mutations.