Establishment of rat embryonic cells in vitro: Relationship of DNA synthesis, senescence, and acquisition of unlimited growth potential

Abstract

Evidence is presented that rat embryo cultures undergo an in vitro aging process similar to that described for mouse embryo, chick, and human cell cultures. Measurements of the percentage of cells capable of incorporating [ 3H]thymidine at each passage revealed that newly explanted rat embryo cells displayed an early decline in proliferative capacity with repeated subcultivation in vitro. This decline in cell doubling capacity was reflected by a parallel reduction in the rate of cell proliferation. Time-lapse microcinematographic analysis also revealed lengthened interdivision times for many cells, and an increase in the fraction of cells observed which did not undergo cytokinesis during the period of observation. Transformation into a cell line with indeterminant growth occurred at about the tenth passage, when the cell proliferation rate and percentage of cells able to incorporate [ 3H]thymidine rapidly increased. In contrast to mouse cells, which generally are heteroploid and acquire the ability to produce tumors prior to the twentieth passage, rat embryo cultures remained diploid and non-tumorigenic during a similar period in culture. These results provide evidence that although rat embryo cell cultures generally proliferate indefinitely, they initially exhibit in vitro cellular age-related characteristics similar to human cells.