Gpt delta transgenic mouse: a novel approach for molecular dissection of deletion mutations in vivo

Human genome is continuously exposed to various DNA damaging agents including reactive oxygen species. Of various forms of DNA damage, double-strand breaks (DSBs) in DNA are the most detrimental because of the mutagenicity and cytotoxicity. To combat the serious threats posed by DSBs, cells evolved various homologous and non-homologous recombination repair mechanisms. However, some repair mechanisms appear to be involved in the induction of genome rearrangements such as deletions. To analyze the deletion mutations in a whole body system, gpt delta mice were established. In this mouse model, deletions in lambda DNA integrated in the chromosome are preferentially selected as Spi- phages, which can then be subjected for molecular analysis. Here, we reported the sequence characteristics of deletions induced by ionizing radiations in the liver, ultraviolet light B in the epidermis, mitomycin C in the bone marrow and heterocyclic amine PhIP in the colon. To our knowledge, this is the first report in which in vivo deletion mutations are systematically analyzed at the molecular level. About half of the large deletions occur between short direct-repeat sequences and the remainder had flush ends, suggesting that they are generated during the repair of DSBs in DNA. The results also suggest that mutation induction and repair mechanisms may vary depending on the type of organs/tissues examined, i.e., germ cells versus somatic cells or highly proliferating cells versus slowly proliferating cells. Possible mechanisms of intrachromosomal deletion mutations are discussed.