Cell cycle arrest induced by radiation in cultured silkworm cells

The silkworm, Bombyx mori, is known to be more resistant to ionizing radiation (IR) compared with mammals, but detailed processes underlying this resistance have remained largely unexplored. In this study, we have confirmed that silkworm larvae survived and showed no effect in the apparent reproduction ability after the irradiation of high doses of γ -ray. We have then observed the effects of γ -irradiation to cells of the silkworm cell line BmN4, which showed marked cell-cycle arrest at the G₂/M phase, but not at the G₁, or S phases. These cells did not undergo apoptosis after γ -ray irradiation in contrast to the mammalian cells wherein G₁, arrests after IR causes apoptosis. After UV-C radiation to cells of BmN4 and Sf21 (a Spodoptera frugiperuda cell line), S-phase checkpoint activation was provoked. But there was also no observation of cell death in BmN4 cells, in contrast to Sf21 cells. Based on these results, we proposed that the extraordinary tolerance of induced DNA injury or the elimination of cell death programs after irradiation is a possible cause of the irradiation resistance in the silkworm cells.