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Updated: Aug 4, 2026
Assessing Somatic Hypermutation in Ramos B Cells after Overexpression or Knockdown of Specific Genes
Published on: November 1, 2011
Hypermutation in bacteria and other cellular systems
1MRC Cell Mutation Unit, University of Sussex, Brighton, UK. b.a.bridges@sussex.ac.uk
Abstract:
A temporary state of hypermutation can in principle arise through an increase in the rate of polymerase errors (which may or may not be triggered by template damage) and/or through abrogation of fidelity mechanisms such as proofreading and mismatch correction. In bacteria there are numerous examples of transient mutator states, often occurring as a consequence of stress. They may be targeted to certain regions of the DNA, for example by transcription or by recombination. The initial errors are made by various DNA polymerases which vary in their error-proneness: several are inducible and are under the control of the SOS system. There are several structurally related polymerases in mammals that have recently come to light and that have unusual properties, such as the ability to carry out 'accurate' translesion synthesis opposite sites of template damage or the possession of exceedingly high misincorporation rates. In bacteria the initial errors may be genuinely spontaneous polymerase errors or they may be triggered by damage to the template strand, for example as a result of attack by active oxidative species such as singlet oxygen. In mammalian cells, hypermutable states persisting for many generations have been shown to be induced by various agents, not all of them DNA damaging agents. A hypermutable state induced by ionizing radiation in male germ cells in the mouse results in a high rate of sequence errors in certain unstable minisatellite loci; the mechanism is unclear but believed to be associated with recombination events.
Insights
Transient hypermutation states arise from increased polymerase errors or reduced DNA repair. These stress-induced mutator states in bacteria and mammals can target specific DNA regions, impacting genetic stability.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Hypermutation, a temporary increase in mutation rate, can occur via elevated polymerase errors or compromised DNA fidelity mechanisms like proofreading and mismatch correction.
- Transient mutator states are observed in bacteria, often stress-induced and potentially targeted to specific DNA regions through transcription or recombination.
- Mammals possess novel DNA polymerases with unique properties, including accurate translesion synthesis and high misincorporation rates.
Purpose of the Study:
- To explore the mechanisms underlying transient hypermutation states in both bacterial and mammalian systems.
- To investigate the role of DNA polymerases and fidelity mechanisms in generating hypermutable conditions.
- To understand how external factors, including DNA damage and other agents, can induce persistent hypermutation.
Main Methods:
- Analysis of DNA polymerase error rates and fidelity mechanisms.
- Investigation of inducible DNA repair systems, such as the SOS response in bacteria.
- Examination of hypermutation induction by various agents, including ionizing radiation, in mammalian germ cells.
Main Results:
- Bacterial transient mutator states are often stress-induced and can be influenced by DNA polymerase error-proneness and inducible repair pathways.
- Mammalian cells exhibit polymerases with high misincorporation rates and capabilities for translesion synthesis.
- Ionizing radiation can induce persistent hypermutation in mouse male germ cells, affecting specific DNA loci, with mechanisms potentially involving recombination.
Conclusions:
- Transient hypermutation is a complex phenomenon involving interplay between DNA polymerases, fidelity mechanisms, and environmental factors.
- Understanding these mechanisms is crucial for comprehending genome instability and evolution in diverse organisms.
- Further research is needed to elucidate the precise molecular mechanisms, particularly recombination's role in radiation-induced hypermutation.
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