Abstract: This invention provides a novel murine cultured cell line which is derived from primary mouse embryo fibroblasts and which exhibits inducer-regulated growth kinetics. The cell line has the potential to grow either linearly or exponentially depending on exposure to an appropriate inducing agent. A corresponding cell line that does not respond to the inducing agent is also provided. The paired cell line system provides a valuable research tool for the development of therapeutic agents that target cells exhibiting deregulated growth kinetics, and also enables the identification of potential carcinogenic agents that alter stem cell renewal kinetics.