FIG. 5.

p53-mediated transactivation of p21 is unaffected by p19^ARF deficiency. Brains were examined from nontransgenic (A and B), TgT₁₂₁;p19^ARF+/+ (C and D), TgT₁₂₁;p19^ARF−/− (E and F), and TgT₁₂₁;p53^−/− (G and H) mice. RNA in situ hybridization was performed on brain sections using an antisense p21 RNA probe and viewed by dark-field microscopy (B, D, F, and H). Adjacent sections were stained with H & E and viewed by bright-field microscopy to show the location and morphology of the CP (A, C, E, and G). No p21 expression is detected in normal CP (B). p21 expression is induced by expression of T₁₂₁ (D) and remains unchanged in the absence of p19^ARF (F). T₁₂₁-induced p21 expression in CP requires functional p53 (H) (18). The bar in panel H is equal to 200 μm; all panels are of the same magnification. br, brain tissue.