Fig. 7: Model of RECQ4 coordination with MUS81 in processing replication/recombination intermediates.

MUS81 interacts with RECQ4 in the S phase and stimulates MUS81-EME2 to resolve replication, recombination intermediates/stalled replication forks. During the G2/M transition, RECQ4 further activates MUS81 in the form of MUS81-EME1 which helps in the resolution of Holliday junction/late replication intermediates, at this stage MUS81 foci are visible and colocalise predominantly with telomeres and partially with centromeres. The proper operation and activation of MUS81 complexes play a crucial role in ensuring a seamless transition from prometaphase to anaphase by preventing misalignment and the build-up of UFBs (with TUBs being more vulnerable in ALT-positive cells). These actions ultimately prevent the formation of micronuclei, which can lead to aneuploidy and disease development, including RTS. Loss of RECQ4 in the background of GEN1 knockout makes the cells very sick further proposing GEN1 as an essential resolution pathway which possibly is the final resolution check during the progression of the cell cycle as GEN1 is only accessible to DNA during the mitotic phase. Conversely, the depletion of both BLM and RECQ4 leads to an increase in unresolved SCEs, as evidenced by the presence of more UFBs per cell. Scale bar = 5 µm. Created in BioRender. Ashraf, R. (2025) https://BioRender.com/o78n251.