The effect of Necdin depletion on premature senescence. (A) Protein expression level in IMR90 cells showed efficient depletion in Necdin expression by shRNA and overexpression of RasV12, which served as a positive control of senescence induction. (B) Senescence-associated β-galactosidase staining 14 days after lentiviral infection demonstrated senescence only in RasV12-expressing cells. (C) Quantification of senescent cells represented by the average of SA-β-gal positive cells. Mean of six different fields ± standard deviation.