Figure 2. Transcriptional activity of p53 target genes in senescent WI-38 fibroblasts. (A) Basal transcription of p53 target genes is not compromised in senescent cells. Total RNA from early passage and senescent WI-38 cells was isolated and the expression of specific mRNAs was determined by quantitative PCR. Expression levels of each individual mRNA (from early passage and senescent cells) were normalized to 18S rRNA. Expression levels in senescent cells were calculated as fold change from the expression levels in early passage cells. The standard deviation (SD) was calculated from four independent experiments. (B) Basal expression levels of p53-regulated microRNA in senescent cells. Expression levels of individual microRNAs from early passage and senescent cells were determined by quantitative PCR, and normalized to RNU48 as an internal control. Expression levels in senescent cells were calculated and presented as in (A).