Figure 4.

Limitations of the G2/M checkpoint. The activation of the G2/M checkpoint is a fast but insensitive process. Low-dose irradiation fails to completely prevent entry into mitosis resulting in many cells entering mitosis with double-strand breaks (DSBs). Higher doses (≥0.5–1 Gy) fully initiate the G2/M checkpoint with only a few cells escaping arrest. The duration of the G2 arrest increases with dose. However, the G2/M checkpoint is not maintained until the completion of DSB repair but cells are released when they harbor 10-20 γH2AX foci. This limitation results in many cells entering mitosis with a substantial amount of unrepaired DSBs. The figure depicts entry into mitosis of asynchronously irradiated cells. pSer 10-H3 was used to assess mitotic cells at various times post irradiation. (See colour version of this figure online at www.informahealthcare.com/bmg)