Chromosome abnormalities associated with salivary gland epithelial cell lines transformed in vitro and in vivo with evidence of a role for genetic imbalance in transformation.

Chromosomal abnormalities associated with five in vitro-transformed male mouse salivary gland epithelial cell lines were compared with those in three cell lines derived from in vivo-induced tumors. All cell lines were hypotetraploid. Structural chromosome abnormalities were found in all cell lines, but no consistent aberration was detected. Nevertheless, losses of chromosomes 1, 4, 7, 9, and 14 were observed in all of the in vitro-transformed cell lines. With the possible exception of chromosome 1, the same chromosome losses were noted in the in vivo-transformed cell lines. In addition, a consistent feature of both in vitro- and in vivo-transformed cell lines was the presence of double minute chromosomes and homogeneously staining regions. Where both of these chromosome types were present in the same cell line, they were mutually exclusive. The Y chromosome was absent in nearly all of the cell lines. These findings are consistent with the view that, in salivary gland epithelium, the malignant phenotype may result from a genetic imbalance caused by specific chromosome losses from tetraploid cells.