Figure 2

Over-expression of MX1 mRNA in fibroblasts with +21. A, Scatter plot of the GeneChip data for MX1, showing the range of expression of this gene in +21 and control fibroblasts at early and late passage. The data in this figure are from the control and +21 fibroblast lines at the passage numbers and percentage of cells positive for acid beta-galactosidase listed in Table 1. B, northern blots showing the over-expression of MX1 mRNA, particularly with increasing passage, in a +21 fibroblast line (DS1) compared to a control fibroblast line (C1). Passage number is indicated above each lane. Re-hybridization with a GAPDH cDNA probe is shown as a loading control. The blots were stripped and re-hybridized with an IFI27 cDNA probe, indicating that this interferon-inducible gene also becomes over-expressed as the cells senesce; but with somewhat less differential expression than MX1. Similar northern blotting results were obtained with two other control and two other +21 fibroblast lines (data not shown). C, Quantitation of the northern blot signals by Phosphorimaging shows increasing MX1 mRNA (normalized to GAPDH) as a function of passage number in +21 fibroblasts, with a more modest increase in control fibroblasts.