Dissociation of Cell Growth and DNA Synthesis and Alteration of the Nucleo-Cytoplasmic Ratio in Growing Embryonal Carcinoma Cells: (nucleo-cytoplasmic ratio/cell cycle/differentiation).

The relationship between the two subcycles 'the cell-growth cycle' (CGC) and the 'DNA-division cycle' (DDC) were examined in the pluripotent embryonal carcinoma cell line PCC3 N/I. This line shows intraclonal bimodal-like heterogeneity in growth rate. A combined protein (mass) and DNA staining method was used to evaluate the relationship between DDC and CGC at various stages in the cell cycle. The results revealed dissociation of the two subcycles and the mass distributions at certain points in the cell cycle reflected the bimodality reported by us for intermitotic time (IDT) distribution. The results were applied to a model called 'The Two-subcycles Cell Cycle Model' (TSCM). This model predicts that the period of DDC (Pre-S+S-G -M) is fairly constant, while the CGC varies, being the main cause of the growth heterogeneity observed in this line. A point of growth rate regulation (PGRR) in G was thought to coincide with the start of CGC. These results reveal a mechanism by which the nucleo-cytoplasmic ratio of the cells can change from one cell cycle to the next.