Generation of large homozygous chromosomal segments by mitotic recombination during lymphomagenesis in F1 hybrid mice

The loss of heterozygosity (LOH) has been reported in numerous neoplasms in both human and animals, and has often been observed in chromosomal regions, which contain tumor-suppressor genes. We previously found frequent LOH on chromosomes 4, 12 and 19 in radiation-induced lymphomas from (BALB/cHeA x STS/A)F-1 hybrid mice by allelotype analysis at polymorphic microsatellite loci. In this study, to elucidate the nature of allelic losses, we refined the loss regions on chromosomes 4, 12 and 19 of the tumors from the F, mice and then analyzed them cytogenetically. The results represent evidence of a wide range of allelic losses owing to mitotic recombination on chromosomes 4 and 19 in the tumors, possibly reflecting functional losses of putative tumor-suppressor genes. It is suggested that the generation of these large homozygous chromosomal segments probably containing the affected genes is one of the genetic alterations responsible for tumorigenesis.