FIG. 4.

mad3^−/− embryos show increased sensitivity to gamma irradiation. Shown are results of TUNEL detection of apoptotic neural precursor cells in transverse sections of mad3^+/+ (A) and mad3^−/− (B) neural tube 3 h after irradiation at 200 rads in utero. The counterstain is hematoxylin. Brown apoptotic nuclei accumulated at the periphery of the VZ and in the lumen of the neural tube more readily in mad3-deficient embryos. Cell counting indicated a significant increase in dead cells in the mad3^−/− neural tubes over those in the wild type (P < 0.05). Wild-type littermate control mice contained an average of 11.8 ± 2.7 apoptotic nuclei while mad3-null mice contained an average of 57.5 ± 5.8 apoptotic nuclei in the lumen of the neural tube.