Spontaneous mutation in Big Blue® mice from fetus to old age: Tissue‐specific time courses of mutation frequency but similar mutation types

Abstract

Transgenic mouse mutation detection systems permit rapid determination of the frequency and type of mutations allowing direct examination of mutational markers for aging, neurodegeneration, and cancer. The Big Blue transgenic mouse mutation detection system was used to determine the frequency and nature of spontaneous mutations versus age in multiple tissue types. Nuclear DNA was extracted from whole fetus at 13.5 days postcoitus (dpc) and from six tissues postbirth (cerebellum, forebrain, thymus, liver, adipose tissue, and male germline) of Big Blue transgenic mice at four ages: 10 days and at 3, 10, and 25 months postbirth. Forty million total plaque-forming units (pfu) were screened. The time course of mutation frequency with age had a significantly different shape in different tissues (P < 10(-6)). By 13.5 dpc, the whole fetus mutation frequency had already started increasing from the theoretical zero at conception to a value that was about one-half the mid-adulthood (3-10 months) average. From 10 days to 3 months, mutation frequency increased significantly in liver (P = 0.007) and showed an increasing trend in cerebellum, forebrain, and thymus. From 3 to 10 months, there was no significant change in mutation frequency in any tissue examined. From 10 to 25 months, the mutation frequency increased significantly in liver (P < 10(-6)) and adipose tissue (P = 0.002), but not in the other tissues examined (cerebellum, forebrain, and male germline). It is of interest that the mutation frequency in the male germline is consistently the lowest, remaining essentially unchanged in old age. The spectrum of mutation types was unaltered with age, tissue type and gender, although, as previously reported, tandem GG-->TT mutations are tissue specific and show significant increases with age and certain hotspots (Buettner VL et al. [1999]: Environ Mol Mutagen 33:320-324; Hill KA et al. [2003]: Mutat Res 534:173-186). The spectrum of mutation types was generally the same for all tissue types, despite the tissue-specific increases in mutation frequency with age. These data provide a useful reference for future studies of endogenous and exogenous mutagenesis.

Age-dependent accumulation of recombinant cells in the mouse pancreas revealed byin situfluorescence imaging

“…The effect of age on these classes of mutations appears to be strongly tissue-dependent. In certain tissues, such as brain and testis, the mutant frequency remains fairly constant (33)(34)(35). In contrast, for liver and bladder, mutant cell frequency increases with age similar to what has been observed for the pancreas in these studies (33)(34)(35).…”

“…In certain tissues, such as brain and testis, the mutant frequency remains fairly constant (33)(34)(35). In contrast, for liver and bladder, mutant cell frequency increases with age similar to what has been observed for the pancreas in these studies (33)(34)(35). It is interesting to speculate that for tissues in which spontaneous mutations accumulate with age, mutagenic exposures during adult life may have a greater influence on cancer risk.…”

“…Other mouse models, including BigBlue (33,34), MutaMouse (35), and LacZ (36), have been used to examine changes in the frequency of point mutations and small deletions with age. The effect of age on these classes of mutations appears to be strongly tissue-dependent.…”

Preferential occurrence of 1-2 microindels

“…Microindels were assembled from a collection of 6,016 Big Blue s lacI independent mutations that had been collected since 1994 [Nishino et al, 1995aBuettner et al, 1996aBuettner et al, ,b, 1997Buettner et al, , 1999Buettner et al, , 2000Moore et al, 1999;Kunishige et al, 2001;Hill et al, 2003Hill et al, , 2004aHill et al, ,b, 2005. All of the mice were housed in isolated airfiltered cages within a barrier facility according to a protocol approved by our institutional animal care and use committee.…”

“…This assay has been used extensively since it was first introduced over 15 years ago. An extensive database of spontaneous mutations has been assembled in our laboratory, and 11 categories of mutation types have been studied extensively [Nishino et al, 1995aBuettner et al, 1996aBuettner et al, ,b, 1997Buettner et al, , 1999Buettner et al, , 2000Moore et al, 1999;Kunishige et al, 2001;Hill et al, 2003Hill et al, , 2004aHill et al, ,b, 2005. Our database of spontaneous mutations in somatic tissues permits detailed analyses of the features of microindels and pure microinsertions and pure microdeletions.…”