Abstract
A temperature-sensitive cell clone has been isolated from Chinese hamster ovary cells (CHO-KI) after mutagenesis with MNNG and BrdU-light suicide selection. The clone, ts-123, has a tetraploid chromosome complement and grows well at the permissive temperature (33°C). However, when incubated at the non-permissive temperature (39°C), the cell number increases only to a limited extent (2-fold increase) within three days. After this period the majority of cells reach higher degree of polyploidy and cells become multinucleated. The temperature effect is irreversible. Cell cycling analysis with a technique of differential staining of sister chromatids with BrdU-Hoechst reveales that at 39°C, ts-123 cells can replicate chromosomal DNA at least 3-rounds before they cease to grow. The processes of polyploidization and multinucleation in synchronized cells were further examined by autoradiography and time-lapse photomicroscopy. Based on the results of such experiments and findings of continued DNA replication, nuclear division, successive polyploidization or multinucleation, it is concluded that the defective function is associated exclusively with the process of cytokinesis. Polyploidization and multinucleation in ts-123 appear to be due to the incomplete cytokinesis and subsequent fusion of daughter nuclei.
