A cause of variation in clonal morphology of polyoma transformed hamster cells

Abstract

When a mixed cell population of hamster embryo cells is transformed in vitro by polyoma virus (PV), a broad spectrum of morphologically different transformed cell clones can be observed at 7–9 days after virus infection. To test the cause of this morphological variation, two series of experiments were carried out. Series A: 21 homogeneous cell populations, each originating from a single cell, were transformed by PV. In all cases, all the transformed clones in any one such homogeneous population showed the same morphology. In addition, 2 homogeneous populations showed the same clone morphology when transformed either by large-plaque virus or a small-plaque mutant. Series B: Cell cultures made from different embryonic organs were transformed by PV. In each case there was, in comparison to a mixed population from whole embryos, a significant reduction in the spectrum of normal and transformed clone morphologies. The hereditability of clonal morphology in transformed clones was established by recloning 15 clones. Cultures of transformed clones with similar morphologies were examined under several physiological conditions. Morphologically similar clones isolated from a mixed population of embryo cells showed physiological differences, whereas morphologically similar clones isolated from a homogeneous cell population were similar under these conditions. The results indicate that when examined at 7–9 days after virus infection, the normal cell type that is transformed is a major factor controlling the morphology of the transformed clone. The uniformity of transformed clones derived from homogeneous normal cell populations indicates that there is a common mechanism for PV-induced cell transformation.