Cellular senescence:ex vivop53-dependent asymmetric cell kinetics

Cellular senescence is a defining property of euploid cells in culture [1,2]. Cultures derived from cells explanted from tissues of a variety of animal species exhibit a finite number of population doublings before undergoing an irreversible arrest of cell replication. Several genes have been implicated as effectors of senescence in culture. These include genetic components of the Rb and p53 growth regulation pathways [3,4,5,6,7,8] and genes encoding components of telomerase [9,10,11]. The p53 and Rb pathways appear to effect senescence proper, being required for the initial cessation of growth by primary cell cultures [3,8,12,13,14]. In contrast, the ability of telomerase to extend culture life span is limited to cells that have first escaped senescence [8,12,13,14].