A reduction of licensed origins reveals strain-specific replication dynamics in mice

Mamm Genome. 2011 Oct;22(9-10):506-17. doi: 10.1007/s00335-011-9333-7. Epub 2011 May 25.


Replication origin licensing builds a fundamental basis for DNA replication in all eukaryotes. This occurs during the late M to early G1 phases in which chromatin is licensed by loading of the MCM2-7 complex, an essential component of the replicative helicase. In the following S phase, only a minor fraction of chromatin-bound MCM2-7 complexes are activated to unwind the DNA. Therefore, it is proposed that the vast majority of MCM2-7 complexes license dormant origins that can be used as backups. Consistent with this idea, it has been repeatedly demonstrated that a reduction (~60%) in chromatin-bound MCM2-7 complexes has little effect on the density of active origins. In this study, however, we describe the first exception to this observation. A reduction of licensed origins due to Mcm4 ( chaos3 ) homozygosity reduces active origin density in primary embryonic fibroblasts (MEFs) in a C57BL/6J (B6) background. We found that this is associated with an intrinsically lower level of active origins in this background compared to others. B6 Mcm4 ( chaos3/chaos3 ) cells proliferate slowly due to p53-dependent upregulation of p21. In fact, the development of B6 Mcm4 ( chaos3/chaos3 ) mice is impaired and a significant fraction of them die at birth. While inactivation of p53 restores proliferation in B6 Mcm4 ( chaos3/chaos3 ) MEFs, it paradoxically does not rescue animal lethality. These findings indicate that a reduction of licensed origins may cause a more profound effect on cell types with lower densities of active origins. Moreover, p53 is required for the development of mice that suffer from intrinsic replication stress.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Proliferation
  • Cell Transformation, Neoplastic / genetics
  • Chromatin / metabolism
  • Cyclin-Dependent Kinase Inhibitor p21 / genetics
  • DNA Damage
  • DNA Helicases / genetics*
  • DNA Replication*
  • Fetal Viability / genetics
  • Gene Expression Regulation
  • Mice
  • Mice, Inbred C3H
  • Mice, Inbred C57BL
  • Mice, Mutant Strains
  • Mice, Transgenic
  • Minichromosome Maintenance Complex Component 4
  • Proliferating Cell Nuclear Antigen / metabolism
  • Rad51 Recombinase / genetics
  • Replication Origin*
  • Species Specificity
  • Transcription, Genetic
  • Tumor Suppressor Protein p53 / genetics
  • Up-Regulation / genetics


  • Chromatin
  • Cyclin-Dependent Kinase Inhibitor p21
  • Proliferating Cell Nuclear Antigen
  • Tumor Suppressor Protein p53
  • Rad51 Recombinase
  • DNA Helicases
  • Mcm4 protein, mouse
  • Minichromosome Maintenance Complex Component 4