Recruitment of TopBP1 to anaphase bridges is evolutionarily conserved. (A) PICH coats hH2B- and Hoechst-negative UFBs in DT40 cells. Cells (RTP82) expressing PICH-YFP from its endogenous promoter and randomly integrated hH2B-mCherry were stained with Hoechst. Arrowhead indicates a UFB. (B) PICH and TopBP1 colocalize at a subset of UFBs. Cells (RTP149) express TopBP1-YFP and PICH-TFP from their endogenous promoters and hH2B-mCherry. Yellow arrowhead indicates the site of PICH and TopBP1 colocalization at a UFB. Blue arrowhead indicates a PICH-coated UFB without TopBP1. (C) PICH dissociates from UFBs before TopBP1 to form transient sister foci at the termini of the UFB as the cell progresses through anaphase and telophase. Representative time-lapse image sequence of cells (RTP151) expressing TopBP1-YFP-AID and PICH-TFP from their endogenous promoters and randomly integrated OsTIR1 and hH2B-mCherry. Arrowheads indicate TopBP1 structures.