Figure 3.
p53 activity and MEF PCD response at the beginning of mouse development. (A) p53 activity assayed in embryos isolated from mice homozygous for reporter genes expressing enhanced green fluorescence protein driven by either the Cdkn1a/p21 or the Bbc3/Puma gene’s p53 response element.75 At embryonic day E3.5, fluorescence was detected in the inner cell mass (ICM), and trophectoderm (TE) of blastocysts. The large blastocoel cavity identifies these examples as late-stage blastocysts containing early epiblast (Fig. 1). At embryonic day E6.5, fluorescence was detected in the epiblast but not in the extraembryonic tissue of gastrula. (B) MEFs cultured for 24 h with doxorubicin and then stained for “apoptosis-inducing factor” AIFM.51 Scale bar is 15 μm. Translocation of AIFM from mitochondria to nucleus occurred in both p53+/+ and p53−/− cells, thereby confirming non-canonical apoptosis in MEFs treated with 500 nM doxorubicin, but not in MEFs with 50 nM doxorubicin.