Somatic cell hybrids derived from terminally differentiated rhesus cells and established mouse cell lines

The mechanisms of normal cell differentiation in vivo may be related to some features of cellular aging in vitro in that both are considered to be under genetic control. Diploid rhesus choroidal melanocytes and purified peripheral lymphocytes were fused by means of inactivated Sendai virus with three long-term murine cell lines which lacked either hypoxanthine-guanine phosphoribosyl transferase or thymidine kinase. Cell hybrids were selected by their growth in medium containing hypoxanthine, aminopterin, thymidine, and glycine. G-banded chromosomes were analyzed and elements from both the rhesus and the established mouse cell lines were identified in all metaphases. Hybrids derived from choroid X mouse cells contained more than one chromosome set from the mouse, but those between lymphocytes and established cell lines had only one. However, in every combination continuously replicating hybrids were produced; most of them have undergone more than 40 subculture passages. Our results demonstrate not only that DNA synthesis can be re-initiated in postreplicative cells, but also that DNA continues to replicate in a manner consistent with the life span of the long-term cell line parent.