Studies on the transformation of hamster embryo cells in culture by polyoma virus

Differences in properties between normal hamster embryo cells and clonal lines of hamster embryo cells transformed with polyoma virus provided means of selecting for the growth of colonies of transformed cells in the presence of many normal cells. In reconstruction experiments where selective techniques were applied to artificial mixtures of small numbers of transformed cells and large numbers of normal cells, transformed cells could be detected at frequencies of 1 cell in 104 normal cells to 1 cell in 105 normal cells, depending upon the particular transformed line of cells used. Cells of one line, termed line Li, of particular interest because its properties were between those of normal cells and cells of the other transformed lines, could not be satisfactorily detected by any of the selective techniques employed. By means of reconstruction experiments, techniques were developed which succeeded in detecting cells of this line at a frequency of one cell in 104 normal cells. When the selective techniques were applied to cultures immediately after adsorption of virus, transformed cells were detected and selected for by some of the techniques, particularly those that were most successful for line Li. Thus new properties, such as a high relative plating efficiency in media containing low concentrations of serum, on which the techniques depend, are conferred upon cells very soon after infection with virus. The selective techniques succeeded in measuring frequencies of transformation too low to be measured by a nonselective colony assay, and thus provide the basis for an assay for transformation of considerably increased sensitivity.