Maintenance of near-diploid karyotype of PA-1 human ovarian teratocarcinoma cells due to death of polyploid cells by chromosome fragmentation/pulverization

Chromosome instability (polyploidy or aneuploidy) is one of the characteris tics of malignant tumors. Human teratocarcinoma cell line PA-I, which was e stablished more than 10 years ago, consists of a majority of near-diploid c ells and a minority of polyploid cells, indicating that it is karyologicall y very stable. In the present study we investigated this genomic stability from the view point of cytogenetics. Cleavages and breaks in the chromosome were found in the metaphase of PA-1 polyploid cells, accompanied by the fo rmation of polynucleosomal DNA fragments. These findings were absent in the near-diploid cells. In addition, polyploid cells did not show colony-forma tion ability by in situ analysis of cytogenetics in each colony. Thus, the maintenance of the near-diploid karyotype in PA-1 cells may be due to a blo ckage in the M-phase of the polyploid cells by functional mitotic checkpoin ts, if any, leading to cell death due to inability to enter the next cell c ycle.