Effects of the scid mutation on X-ray-induced deletions in the brain and spleen of gpt delta mice

DNA-dependent protein kinase (DNA-PK), consisting of a Ku heterodimer (Ku70/80) and a large catalytic subunit (DNA-PKcs), plays an important role in the repair of DNA double-strand breaks via non-homologous end-joining (NHEJ) in mammalian cells. Severe combined immunodeficient (scid) mice carry a mutation in the gene encoding DNA-PKcs and are sensitive to ionizing radiation. To examine the roles of DNA-PKcs in the generation of deletion mutations in vivo, we crossed scid mice with gpt delta transgenic mice for detecting mutations. The scid and wild-type (WT) gpt delta transgenic mice were irradiated with a single X-ray dose of 10 Gy, and Spi− mutant frequencies (MFs) were determined in the brain and spleen 2 days after irradiation. Irradiation with X-rays significantly enhanced Spi− MF in both organs in the scid and WT mice. The MFs in the brain of irradiated scid mice were significantly lower than those in WT mice, i.e., 2.9 ± 1.0 × 10− 6 versus 5.0 ± 1.1 × 10− 6 (P < 0.001), respectively. In the spleen, however, both mouse strains exhibited similar MFs, i.e., 4.1 ± 1.8 × 10− 6 versus 4.8 ± 1.4 × 10− 6. Unirradiated scid and WT mice did not exhibit significant differences in MFs in either organ. DNA-PKcs is unessential for the induction of deletion mutations in the spleen, while it plays a role in this in the brain. Therefore, the contribution of DNA-PKcs to NHEJ may be organ-specific.