Figure 1. The Cdkn1a variant 2 transcript is preferentially induced during aging. (A) We designed primers (black arrows) to specifically detect Cdkn1a variant 1 and 2 transcripts, spanning the first and second exons in each case. The protein-coding region is indicated as well as the ATG start codon (brown arrow). Transcription starts at +1 for p21var1 and at -2790 for p21var2. The first and last bases of each exon are also indicated. (B) mRNA levels of p21var1 and p21var2 in the livers of male mice aged 2 to 30 months of age, normalized to levels in livers of 2 month-old animals. (C–G) Levels of each Cdkn1a transcript were assessed in 2 (young) and 24 (old) month-old mice. Animals were young males (n = 12), young females (n = 12), old males (n =14-15) and old females (n = 14-15). Results are shown for (C) liver, (D) adipose tissue, (E) kidney, (F) heart and (G) lung. In (C–G) data were normalized to p21var1 levels in young mice. Note Y axes are log-2 scales. 1-way ANOVA and Tukey post-tests were applied. * p < 0.05, ** p < 0.01, *** p < 0.001, ns = not-significant.