Efficient detection of deletions induced by a single treatment of mitomycin C in transgenic mouse gpt delta using the Spi(-) selection

Transgenic rodent mutation assays permit the detection and molecular analys is of various types of gene mutations, such as base changes and Frameshifts , in a number of tissues. it is reported, however, that deletion mutations ore not efficiently detected by the assays, in particular those using lambd a phage shuttle vectors. Recently, a new transgenic mouse model, i.e., gpt delta, has been developed to selectively detect some types of deletions by Spi(-) selection. Spi- selection has an advantage over the other selections to preferentially identify deletions because only lambda phages deficient in both the red and gam gene functions are allowed to form phage plaques. I n this study, we examined whether in vivo deletions induced by the treatmen t of mitomycin C (MMC) are detect able by the Spi- assay in the mouse model . The mice were treated with MMC (0.5, 1.0, 2.0, and 4.0 mg/kg, single intr aperitoneal injection) and sacrificed 14 days after the dosing. The treatme nt at 4.0 mg/kg approximately doubled the mutant Frequency of Spi- in the b one marrow, i.e., 2.52 x 10(-6) vs. 1.31 x 10-6. The molecular analyses usi ng polymerase chain reaction (PCR) and DNA sequencing indicated that seven Spi(-) mutants at 4.0 mg/kg group had deletions with molecular sizes From 0 .8 kilo basepairs (kb) to 8.5 kb, whereas no such deletions were observed i n the Spi- mutants in the control group. The results suggest that deletions induced by MMC in the bone marrow are efficiently detectable by Spi(-) sel ection and also that the molecular analyses are useful to evaluate the sign ificance of a marginal increase in mutant frequency in the transgenic roden t mutation assays. (C) 1999 Wiley-Liss, Inc.