Progressive loss of DNA and lowering of the chromosomal mode in chemically transformed C3H/10T1/2 cells during development of their oncogenic potential.

When mouse embryo C3H/10T1/2 fibroblasts are transformed by 7,12-dimethylbenz(a)anthracene, the development of oncogenic potential is associated with characteristic morphological changes, which can be classified into three types and which are also dependent upon the number of cell passages. This paper reports changes in DNA content studied by flow cytometry of ethidium bromide-stained nuclei and changes in chromosome number observed by counting 50 randomly chosen Colcemid-arrested metaphases of each cell culture population. The nontransformed cells maintained a stable hypotetraploid DNA content. The morphologically transformed cell showed no changes during their first passages in culture, except for the appearance of small polyploid subpopulations. The occurrence and increase of the oncogenic potential in the higher passages in the transformed cells were associated with decrease in nuclear DNA content as well as reduction in chromosome number. For the most oncogenic passages, the reduction of chromosome numbers was considerable, and there was no overlapping between the chromosome numbers of the original and the most oncogenic cells. This finding supports the view that the transformation process is a result of progression (chromosomal changes and subsequent selection) and not only of the selection of cells that were present at the start of the culture. The genetic material obviously lost in the most oncogenic cells may be different from the DNA material lost by the cells that remained nononcogenic.