The Site of the Target Region for Radiation-Induced Mitotic Delay in Cultured Mammalian Cells

Previous work had shown that irradiation of much of the cytoplasm of individual Chinese hamster fibroblasts with large doses of α-particles from a polonium-tipped microneedle did not delay their proliferation. The present paper shows that 1000 R of x-rays and small numbers of α-particles penetrating a few microns into the nucleus produced 8-9 hours and 16 hours mitotic delay, respectively. Hence the targets for mitotic delay are either nuclear or in the immediately perinuclear cytoplasm.