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System issues: Temporal and molecular characteristics of lacZ mutations in somatic tissues of transgenic mice
Author(s) -
Douglas George R.,
Jiao Jianli,
Gingerich John D.,
Soper Lynda M.,
Gossen Jan A.
Publication year - 1996
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(1996)28:4<317::aid-em4>3.0.co;2-8
Subject(s) - somatic cell , biology , genetics , transgene , mutation , genetically modified mouse , gene , computational biology , microbiology and biotechnology
In order to help establish criteria for optimizing protocols for in vivo mutation studies, lacZ transgenic mice (Muta™ mouse) were treated with five consecutive daily doses of ethylnitrosourea (50 mg/kg), sampled at times up to 55 days after treatment, and mutant frequencies and DNA sequences determined for liver and bone marrow. In the bone marrow, the mutant frequency rose very rapidly in the first 5 days after treatment to 34 times the control frequency. Subsequently, there was a broad peak where the mutant frequency did not vary significantly, although it did appear to begin to decline after 45 days. In contrast, in the liver, the peak mutant frequency (11 times the control frequency) was not achieved until 35 days, after which there appeared to be a slow decline up to 55 days, which was not statistically significant. Once the maximum mutant frequency was reached, the mutation spectra in the two tissues were indistinguishable. In contrast to the G:C → A:T transitions in 5′‐CpG sites characteristic of untreated mice, A:T → T:A transversions and A:T → G:C transitions were prominent in both liver and bone marrow of ENU‐treated mice, suggesting the involvement of unrepaired O 2 ‐and O 4 ‐ethylthymine adducts. In addition, G:C → T:A transversions were induced in liver. This study demonstrates the possibility that although tissues may have different mutation fixation times, a single mutation fixation time equal to the longest time may be appropriate for in vivo mutation studies, provided that the mutation frequency does not decline appreciably after the peak is reached. This study also illustrates the necessity of ensuring that mutation characteristics are determined after optimal fixation has occurred. © 1996 Wiley‐Liss, Inc.