Motif-primed polymerase chain reaction-based allelotype of sarcomas induced by 3-methylcholanthrene in interspecific hybrid mice.

Loss of heterozygosity (LOH) occurs commonly in some human tumors and is thought to reflect the selective pressure exerted by tumor suppressor genes. The purpose of this study was to examine the genomic location and relative frequency of LOH of chemically induced tumors in an established mouse model for chemical carcinogenesis. Twenty-four tumors were induced by subcutaneous injection of 3-methylcholanthrene into inter-subspecific hybrid (C57BL/6J x SPRET/Ei)F1 mice. Tumors were diagnosed as poorly differentiated, spindle cell sarcomas. DNA isolated from cell cultures derived from the sarcomas was analysed for LOH using a multi-locus genome scanning technique, motif-primed PCR, followed by conventional simple sequence length polymorphism (SSLP) PCR markers. Ninety-one motif-primed PCR products and seven SSLP markers were evaluated, covering segments of 39 out of 41 chromosomes. LOH was extremely rare; average fractional allelic loss per tumor was less than 0.01 suggesting a remarkable genetic stability of the tumors and that genetic events leading to transformation are only rarely revealed as LOH. However, some regions exhibiting LOH were identified encompassing both known and hypothesized tumor suppressor loci such as Trp53. These data indicate that motif-primed PCR is an efficient method of scanning the genome of interspecific sarcomas for rare mutational events generating LOH during tumor induction. Cell lines derived from the sarcomas promise to be useful for identifying genes whose inactivation causes increased malignancy during tumor progression.