High-resolution mapping of mitotic DNA synthesis regions and common fragile sites in the human genome through direct sequencing

Cell Res. 2020 Nov;30(11):997-1008. doi: 10.1038/s41422-020-0358-x. Epub 2020 Jun 19.


DNA replication stress, a feature of human cancers, often leads to instability at specific genomic loci, such as the common fragile sites (CFSs). Cells experiencing DNA replication stress may also exhibit mitotic DNA synthesis (MiDAS). To understand the physiological function of MiDAS and its relationship to CFSs, we mapped, at high resolution, the genomic sites of MiDAS in cells treated with the DNA polymerase inhibitor aphidicolin. Sites of MiDAS were evident as well-defined peaks that were largely conserved between cell lines and encompassed all known CFSs. The MiDAS peaks mapped within large, transcribed, origin-poor genomic regions. In cells that had been treated with aphidicolin, these regions remained unreplicated even in late S phase; MiDAS then served to complete their replication after the cells entered mitosis. Interestingly, leading and lagging strand synthesis were uncoupled in MiDAS, consistent with MiDAS being a form of break-induced replication, a repair mechanism for collapsed DNA replication forks. Our results provide a better understanding of the mechanisms leading to genomic instability at CFSs and in cancer cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line, Tumor
  • Chromosome Breakage
  • Chromosome Fragile Sites / genetics*
  • DNA / biosynthesis*
  • DNA Replication Timing / genetics
  • Genome, Human*
  • Genomic Instability
  • Humans
  • Mitosis / genetics*
  • Molecular Sequence Annotation
  • Neoplasms / genetics
  • Replication Origin / genetics
  • Sequence Analysis, DNA*


  • DNA