Nucleoplasmic bridges in normal and CML CD34⁺ cells after radiation exposure. (A) The sequence of events leading to BFB formation after exposure of cells to radiation. DNA DSBs resulting from radiation exposure on repair may result in formation of a dicentric chromosome. The 2 centromeres in the dicentric chromosome will attach to opposite poles during cell division, leading to bridge formation and subsequent tearing of the chromosome. The broken end of the chromosome may fuse with another broken chromosome, leading to formation of another dicentric initiating another BFB cycle. (B) Representative images of nucleoplasmic bridges (original magnification ×630). Formation of nucleoplasmic bridges at 24 hours (1 cell division) and 72 hours (3 or 4 cell divisions) after exposure to radiation in (C) normal CD34⁺ cells (n = 3) and (D) CML CD34⁺ cells (n = 3). Results represent mean ± SEM of multiple experiments. (E) Nucleoplasmic bridges at 24 hours (1 cell division) and 144 hours (6 or 7 cell divisions) in CML BC CD34⁺ cells (n = 6) with and without exposure to radiation. (F) Formation of nucleoplasmic bridges in CFSE^low and CFSE^high cell populations from CML CP CD34⁺ cells and MBA-4 cells after exposure to radiation. No significant difference in bridge formation was observed between these 2 populations in both cell types.