Frequency of nuclear grooves in lung lesions of irradiated mice. Panel A: Representative histological images of lung AC tissue with nuclear grooves. Images show lung ACs with low (–), moderate (+), or high (++) incidence of nuclear grooves. Nuclear grooves are indicated by arrowheads in each inset. Panels B–E: Frequency of nuclear grooves in lung AD and AC of male (panels B and D) and female (panels C and E) mice. Scale bars, 100 µm. Insets show high-magnification images (scale bars, 25 µm). **P < 0.01 vs. no irradiation.