Doubling potential of fibroblasts from different species after ionising radiation

Abstract

IT is well known that chicken fibroblasts invariably die after a certain number of doublings in vitro (cell senescence) and that they have never been established by any chemical or physical agent¹. On the other hand, mouse fibroblasts invariably acquire spontaneously an infinite growth potential, and transformation can be induced at a high frequency by different oncogenes². Other species like man also yield fibroblasts which never acquire spontaneously the capacity to divide for ever³ but can become permanent cell lines after infection with SV40 virus⁴. Transformation in human fibroblasts has only been unequivocally demonstrated after treatment with certain viruses. This behaviour of fibroblasts in vitro has been attributed to different nutritional requirements⁵. The two approaches to explain the phenomenon can be summarised as intrinsic properties against environmental conditions. We have previously shortened the life-spans of cultivated chicken fibroblasts with low dose rate ionising radiation⁶. We have carried out the same type of experiment with human and mouse fibroblasts and found that the response to ionising radiation fits the relative tendencies of these different fibroblasts to yield permanent cell lines.