Journal Article

Formation and persistence of <i>O</i><sup>6</sup>-ethylguanine in genomic and transgene DNA in liver and brain of λlacZ transgenic mice treated with <i>N</i>-ethyl-<i>N</i>-nitrosourea

Edwin J. Mientjes, Klaus Hochleitner, Anja Luiten-Schuite, Joost H.M. van Delft, Jiirgen Thomale, Frits Berends, Manfred F. Rajewsky, Paul H.M. Lohman and Robert A. Baan

in Carcinogenesis

Volume 17, issue 11, pages 2449-2454
Published in print November 1996 | ISSN: 0143-3334
Published online November 1996 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/17.11.2449
Formation and persistence of
                    O6-ethylguanine in genomic and transgene DNA in
                    liver and brain of λlacZ transgenic mice treated with
                        N-ethyl-N-nitrosourea

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LacZ transgenic mice are suitable for short-term muta-genicity 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 immuno-affinity 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.

Journal Article.  0 words. 

Subjects: Clinical Cytogenetics and Molecular Genetics

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