Karyologic Studies of Normal Cells and of Adenovirus-Type-12-Induced Tumor Cells of the Syrian Hamster23

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Abstract
The karyotype of Syrian hamster-embryo and bone marrow cells was studied and its idiogram constructed as a baseline for a study of hamster tumors induced by human adenovirus type 12 (A-12). A key to the identification of Syrian hamster chromosomes is presented, based on relative chromosome lengths and arm ratios. The Y chromosome was identified as a large submetacentric with an arm ratio of 2.1, equal in size to the second largest pair of autosomes. Chromosome studies were made on primary cultures of hamster embryo, A-12-induced primary hamster tumors in vivo, and the 5th and 12th passages of A-12 hamster tumor cells cultured in vitro. Although most tumor cells were in the diploid range with a modal chromosome number of 44, frequent deviations from the normal or expected karyotype were observed, even in cells with the diploid number of 44 chromosomes (pseudodiploidy). The tumor cells also showed an increased incidence of polyploidy, aneuploidy, loss of acrocentric chromosomes, chromatid breaks, dicentric chromosomes, translocations, and ring chromosomes. All these deviations from the normal hamster cells were observed in primary tumors in vivo as well as in serially cultured tumors in vitro, indicative of a greater karyotypic instability of A-12 tumor cells. In both normal and tumor cells, chromosome #3 occasionally had a visible secondary constriction on the long arm, two thirds of the distance from the centromere, which was sometimes exaggerated to the point of being indistinguishable from a chromosome break.