Accumulation of recombinant chromosomes and low fidelity of transmission of chromosome X DNA markers in γ‐ray–induced lymphomas lacking p53

F 1 offspring of male MSM male mice with a p53 ‐deficient (knockout) allele and normal female BALB/c mice were backcrossed with MSM mice to produce N 2 mice. Female F 1 and N 2 mice were irradiated with γ‐radiation, and thymic lymphomas were obtained from 69 F 1 and 82 N 2 mice heterozygous for X chromosome markers. Of these 151 mice, 91 carried a p53 ‐deficient allele. These lymphomas were analyzed for allelic loss by using four marker loci distributed on X chromosome to assess the stability of the inactive X chromosome, which contributes little to cellular functions. Twenty lymphomas showed allelic loss of all four loci, suggesting loss of a whole inactive X chromosome due to mitotic nondisjunction, whereas 24 lost only a part of an X chromosome, as a result of somatic recombination. The p53 status of the lymphomas was determined by genotyping and allelic loss analysis: 53 had retained two wild‐type p53 alleles, suggesting normal function; 69 had lost both alleles, indicating loss of function; and the remaining 29 had at least one wild‐type p53 allele, so their p53 status was unclear. Compilation of these two data revealed one nondisjunction‐type change and five recombination‐type mutations on X chromosome in 53 lymphomas retaining functional p53. In contrast, 14 and 16 of these alterations, respectively, were observed in 69 lymphomas lacking p53 function. These results suggest that p53 loss significantly increases the accumulation of recombinant chromosomes and decreases the fidelity of mitotic chromosome transmission of the X chromosome in γ‐ray–induced lymphomas. Mol. Carcinog. 24:57–63, 1999. © 1999 Wiley‐Liss, Inc.