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Formation and persistence of O6-ethylguanine in genomic and transgene DNA in liver and brain of lambda(lacZ) transgenic mice treated with N-ethyl-N-nitrosourea. 1996

E J Mientjes, and K Hochleitner, and A Luiten-Schuite, and J H van Delft, and J Thomale, and F Berends, and M F Rajewsky, and P H Lohman, and R A Baan
Department of Molecular Toxicology, TNO Food and Nutrition Research Institute, Rijswijk, The Netherlands.

LacZ transgenic mice are suitable for short-term mutagenicity studies in vivo. Mutagenicity in these mice is determined in the lacZ transgene. Since the lacZ gene is of bacterial origin the question has been raised whether DNA-adduct formation and repair in the transgene are comparable to those in total genomic DNA. Mice were treated with N-ethyl-N-nitrosourea (ENU) and killed at several time points following treatment. Some mice were pretreated with O6-benzylguanine to inactivate the repair protein O6-alkylguanine-DNA alkyltransferase (AGT). O6-ethylguanine (O6-EtG) was determined in lacZ in liver and brain by means of a monoclonal antibody-based immunoaffinity assay. In addition, O6-EtG and N7-ethylguanine (N7-EtG) were assayed in total genomic DNA of liver and brain with an immunoslotblot procedure. In liver, the initial O6-EtG level in total genomic DNA was 1.6 times that in lacZ. The extent of repair of O6-EtG during the first 1.5 h after treatment was 2.1 times that in lacZ. At later time points, O6-EtG repair was the same. N7-EtG repair in genomic DNA was evident. In contrast to the liver, little repair of O6-EtG in total genomic and lacZ DNA occurred in the brain while N7-EtG was repaired. No initial difference in O6-EtG levels were found in lacZ and genomic brain DNA. These findings indicate that in the liver, total genomic DNA is more accessible than lacZ to ENU and/or the AGT protein, during the first 1.5 h following treatment. Because the difference in O6-EtG levels in the transgene and genomic DNA in the liver is restricted to the first 1.5 h after treatment, while the fixation of mutations occurs at later time points, O6-EtG-induced mutagenesis most likely is also very similar in both types of DNA.

UI MeSH Term Description Entries
D007763 Lac Operon The genetic unit consisting of three structural genes, an operator and a regulatory gene. The regulatory gene controls the synthesis of the three structural genes: BETA-GALACTOSIDASE and beta-galactoside permease (involved with the metabolism of lactose), and beta-thiogalactoside acetyltransferase. Lac Gene,LacZ Genes,Lactose Operon,Gene, Lac,Gene, LacZ,Genes, Lac,Genes, LacZ,Lac Genes,Lac Operons,LacZ Gene,Lactose Operons,Operon, Lac,Operon, Lactose,Operons, Lac,Operons, Lactose
D008099 Liver A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances. Livers
D008822 Mice, Transgenic Laboratory mice that have been produced from a genetically manipulated EGG or EMBRYO, MAMMALIAN. Transgenic Mice,Founder Mice, Transgenic,Mouse, Founder, Transgenic,Mouse, Transgenic,Mice, Transgenic Founder,Transgenic Founder Mice,Transgenic Mouse
D009152 Mutagenicity Tests Tests of chemical substances and physical agents for mutagenic potential. They include microbial, insect, mammalian cell, and whole animal tests. Genetic Toxicity Tests,Genotoxicity Tests,Mutagen Screening,Tests, Genetic Toxicity,Toxicity Tests, Genetic,Genetic Toxicity Test,Genotoxicity Test,Mutagen Screenings,Mutagenicity Test,Screening, Mutagen,Screenings, Mutagen,Test, Genotoxicity,Tests, Genotoxicity,Toxicity Test, Genetic
D009153 Mutagens Chemical agents that increase the rate of genetic mutation by interfering with the function of nucleic acids. A clastogen is a specific mutagen that causes breaks in chromosomes. Clastogen,Clastogens,Genotoxin,Genotoxins,Mutagen
D010582 Bacteriophage lambda A temperate inducible phage and type species of the genus lambda-like viruses, in the family SIPHOVIRIDAE. Its natural host is E. coli K12. Its VIRION contains linear double-stranded DNA with single-stranded 12-base 5' sticky ends. The DNA circularizes on infection. Coliphage lambda,Enterobacteria phage lambda,Phage lambda,lambda Phage
D001921 Brain The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM. Encephalon
D004247 DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA, Double-Stranded,Deoxyribonucleic Acid,ds-DNA,DNA, Double Stranded,Double-Stranded DNA,ds DNA
D004260 DNA Repair The removal of DNA LESIONS and/or restoration of intact DNA strands without BASE PAIR MISMATCHES, intrastrand or interstrand crosslinks, or discontinuities in the DNA sugar-phosphate backbones. DNA Damage Response
D005038 Ethylnitrosourea A nitrosourea compound with alkylating, carcinogenic, and mutagenic properties. Nitrosoethylurea,N-Ethyl-N-nitrosourea,N Ethyl N nitrosourea

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