Figure 1.

Expression of the Ink4a/Arf locus increases with aging. (A) Relative expression. The ratios (log₂ scale) of the expression of cell cycle inhibitors – old (26 months)/young (2.5 months) – from 15 tissues is graphed ± SEM. Each estimate represents the mean of 8–32 quantitative RT-PCR reactions on independent RNA samples derived from 4–6 mice. *Minimum estimate of old/young ratio. (B) Absolute expression. The absolute copy number of p16^INK4a and Arf mRNA molecules (log₁₀ scale) per 90 ng total RNA RT-PCR from 15 tissues of young (2.5 months) and old (26 months) mice is graphed ± SEM. Murine embryo fibroblasts (MEFs) at early (P4) and late (P7) passage are shown for comparison. ^#Maximum estimated expression is indicated, as expression was below the level of detection.