Evidence for altered cell-cycle traverse of the non-modal cells of the heteroploid MCa-11 line

Classic stem cell theory states that the growth of heteroploid cell populations is due to the proliferation of 'main stemline'cells with modal DNA content and chromosome number. Cells with non-modal DNA content and chromosome number are thought to be blocked and/or destroyed at mitosis. To test this, we studied two chromo-somally stable cell populations (mouse bone marrow and WCHE-5 cells) and one heteroploid, chromosomally diverse cell line (MCa-11). The heteroploid MCa-11 cells showed significant ³H]dT labelling for cells with DNA contents below the modal G_o/G₁ peak and above the modal G₂ peaks ( P <0.001). This was consistent with the presence of cells with the non-modal DNA content that were engaged in replicative DNA synthesis. A percentage labelled mitosis analysis showed that MCa-11 cells with non-modal DNA content and chromosome number were able to complete mitosis, although with prolonged pre-karyokinetic time. These results suggest that many non-modal cells present in heteroploid cell populations are capable of continued proliferation.