Mitotic DNA repair by TMEJ suppresses replication stress-induced nuclear envelope reassembly defect.

Replication stress (RS), if not effectively and timely addressed, could result in DNA damage in mitosis. However, the relationship between RS and other mitotic events, such as nuclear envelope (NE) breakdown and reassembly, remains poorly understood. Here we report that RS can lead to NE defect. Importantly, rather than de novo NE rupture, the defect per se is a result of nuclear envelope reassembly defect (NERD) during mitosis. Interestingly, NERD is associated with mitotic DNA damage, and repair of the damage by DNA polymerase theta (Polθ)-mediated end joining (TMEJ) ameliorates NERD. Genomic mapping of lamina associated domains (LADs) by cleavage under targets and tagmentation (CUT&Tag) identifies a population of replication stress-sensitive LADs (RESSLADs). Strikingly, a substantial portion of RESSLADs reside in the common fragile sites (CFSs). The loss of RESSLADs-NE interaction under RS might be attributed to the sustained phosphorylation of Lamin A/C at the sites of NERD. In addition, prominent NE defect is observed under multiple conditions of synthetic lethality. Altogether, these findings establish a link between genome instability and nuclear vulnerability under replication stress.