Fig. 4.

Postmitotic regions in theAtm^−/− cingulate cortex are resistant to radiation-induced apoptosis. In theAtm^−/− cingulate cortex at E15.5, the subventricular zone (SVZ) was markedly resistant to radiation-induced apoptosis. Proliferating cells were identified by Ki67 (a); to identify postmitotic regions that define the SVZ, we used p27 (b) and Tuj1 (c). The SVZ of WT embryos shows radiation-dependent serine-18 phosphorylation of p53 (d, h), whereas theAtm^−/− SVZ does not (f, k). Activated caspase-3 immunoreactivity is shown at 1 hr (e, g) and 4 hr (i, l) after radiation. ISEL+ staining indicates that apoptosis occurs in WT (j), but not inAtm^−/−(m), cingulate cortex SVZ.