ABSTRACT
In 1965, Hayflick proposed that the limited in vitro proliferative potential of normal human fibroblasts in culture was a manifestation of aging at the cellular level. The proliferative potential of the cells depends on the age of the donor, species of the donor, and the site of biopsy. The early work of Littlefield suggested that the limited proliferative potential might be dominant in somatic cell hybrids between senescent cells and young proliferating cells. The introduction of single normal human chromosomes into immortal cell lines represents a considerable refinement over the techniques of somatic cell hybridization involving whole cells. The use of microcell hybrid techniques has allowed researchers to assign genes coding for normal cellular aging processes to one particular human chromosome. In order to explore the feasibility of searching for cDNA clones coding for the inhibitor, researchers microinjected poly (A)+ RNA from senescent cells into young proliferation-competent cells to determine whether inhibitory activity could be conferred by the messenger RNA.
