The effect of Necdin overexpression on cellular life span. Population doubling of an IMR90tetR population expressing inducible Necdin or empty vector (A) with or (B) without doxycycline induction (arrow in A indicates the time where induction began). Population doubling monitoring begins after the selection period where cells achieve PD40 (corresponding to PD0 on the graph). (C) Protein extracts at two different time points showed efficient Necdin induction with doxocyclin. Representative results of three independent experiments.