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Carcinogens induce reversion of the mouse pink-eyed unstable mutation
R H Schiestl1, J Aubrecht, F Khogali
1Department of Molecular and Cellular Toxicology, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA. schiestl@mbcrr.harvard.edu
Abstract:
Deletions and other genome rearrangements are associated with carcinogenesis and inheritable diseases. The pink-eyed unstable (pun) mutation in the mouse is caused by duplication of a 70-kb internal fragment of the p gene. Spontaneous reversion events in homozygous pun/pun mice occur through deletion of a duplicated sequence. Reversion events in premelanocytes in the mouse embryo detected as black spots on the gray fur of the offspring were inducible by the carcinogen x-rays, ethyl methanesulfonate, methyl methanesulfonate, ethyl nitrosourea, benzo[a]pyrene, trichloroethylene, benzene, and sodium arsenate. The latter three carcinogens are not detectable with several in vitro or in vivo mutagenesis assays. We studied the molecular mechanism of the carcinogen-induced reversion events by cDNA analysis using reverse transcriptase-PCR method and identified the induced reversion events as deletions. DNA deletion assays may be sensitive indicators for carcinogen exposure.
Insights
Carcinogen exposure can induce genome rearrangements, specifically deletions, in mice with the pink-eyed unstable (pun) mutation. These DNA deletion assays show promise as sensitive indicators for carcinogen exposure.
Area of Science:
- Genetics
- Molecular Biology
- Toxicology
Background:
- Genome rearrangements like deletions are linked to cancer and inherited diseases.
- The pink-eyed unstable (pun) mutation in mice involves a duplicated p gene fragment.
- Spontaneous reversion in pun/pun mice occurs via deletion of this duplicated sequence.
Purpose of the Study:
- To investigate the molecular mechanism of carcinogen-induced reversion events in the pun mouse model.
- To determine if DNA deletion assays can serve as sensitive indicators for carcinogen exposure.
Main Methods:
- Utilizing the pink-eyed unstable (pun) mouse model.
- Inducing reversion events with various carcinogens (x-rays, EMS, MMS, ENU, B[a]P, TCE, benzene, sodium arsenate).
- Employing cDNA analysis with reverse transcriptase-PCR to identify molecular changes.
Main Results:
- Carcinogen exposure successfully induced reversion events in premelanocytes.
- Identified induced reversion events as deletions at the molecular level.
- Demonstrated that certain carcinogens (TCE, benzene, sodium arsenate) induce deletions detectable by this assay, despite failing other mutagenesis assays.
Conclusions:
- Carcinogen-induced DNA deletions are a key mechanism in the reversion of the pun mutation.
- DNA deletion assays represent a potentially sensitive method for detecting exposure to genotoxic carcinogens.
- This mouse model provides insights into genome instability and carcinogenesis.