The effect of heterozygous point mutations in p53 on apoptosis
in thymocytes. (A) p53-dependent and
-independent apoptosis. Thymocytes of mice of all different
genotypes were isolated (▴, wild type;
●, p53+/−;
■, p53−/−; ○,
p53+/R270H; □,
p53+/P275S) and exposed in
vitro to γ irradiation (500 cGy), doxorubicin (0.2
μg/ml), or dexamethasone (1 μM). At the time points indicated,
thymocytes were stained with annexin V and PI. The relative percentage
of viable cells (negative for both PI and annexin V) for each sample is
shown. All values are normalized to the number of cells remaining
viable in untreated cultures derived from the same animal stained
simultaneously. Data are representatives of ≥2 independent experiments
(i.e., mice). (B) Northern blot of p53 target genes in
thymocytes after γ irradiation (500 cGy). Two or 5 hr after the
treatment, RNA was isolated, and Northern blots were probed with
bax, cyclinG, and gapdh
cDNA probes. (C) Quantitation of Northern blot signals
normalized for expression levels of gapdh (used as a
loading control). ▴, Wild type; ●,
p53+/−; ■,
p53−/−; ○,
p53+/R27OH; and □,
p53+/P275S.