Persistence of red blood cells with Pig-a mutation in p53 knockout mice exposed to X-irradiation.

The Pig-a mutation assay is becoming one of the major experimental procedures used to assess in vivo genotoxicity. The assay allows simple in vivo analysis and enables gene mutations in the hematopoietic system to be measured using high throughput flow cytometry. Previously, we demonstrated that X-irradiation increased the Pig-a mutant frequencies in red blood cells (RBCs) of mice in a radiation dose-dependent manner. In this study, to understand how RBCs with Pig-a mutation induced by X-irradiation persist, we compared Pig-a mutant frequencies between irradiated C57BL/6J (p53(+/+)) mice and irradiated p53 homozygous knockout (p53(-/-)) mice by using the RBC Pig-a assay. After the peak in radiation-induced Pig-a mutant frequencies, a gradual decrease in mutant frequencies in irradiated p53(-/-) mice was observed, while irradiated p53(+/+) mice had a rapid decrease, which suggests that RBCs with Pig-a mutation are eliminated normally in irradiated p53(+/+) mice but not in irradiated p53(-/-) mice due to lack of p53 function. In addition, we also found that the p53 function affected the regulation of Pig-a mutagenesis in aging mice. Our results suggest that p53 function, distinct types of mutation, and the life span of RBCs play key roles in the persistence of Pig-a mutation in the hematopoietic system of RBCs after irradiation.