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Interference in DNA replication can cause mitotic chromosomal breakage unassociated with double-strand breaks
Mari Fujita1, Hiroyuki Sasanuma, Kimiyo N Yamamoto
1Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshidakonoe, Sakyo-ku, Kyoto, Japan.
Plos One
|April 11, 2013
Summary
Chromosomal breaks, crucial for detecting mutagens, are not always double-strand breaks (DSBs). Replication-blocking agents can induce breaks independently of DSB repair pathways, suggesting unreplicated single-strand gaps may cause breaks.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- Morphological analysis of mitotic chromosomes is a standard method for detecting mutagenic compounds and estimating radiation doses.
- The prevailing theory posits that all chromosomal breaks are associated with double-strand breaks (DSBs).
Purpose of the Study:
- To challenge the canonical theory that chromosomal breaks are exclusively linked to double-strand breaks (DSBs).
- To investigate the role of DNA replication stress in inducing chromosomal breaks independent of DSB repair mechanisms.
Main Methods:
- Utilized chicken DT40 and human Nalm-6 cell lines, including wild-type and DSB-repair-deficient variants (lacking homologous recombination and non-homologous end-joining pathways).
- Induced chromosomal breaks using replication-blocking agents: aphidicolin, 5-fluorouracil, and hydroxyurea.
- Quantified mitotic chromosomal breaks in cells exposed to these agents for at least two cell cycles.
Main Results:
- Replication-blocking agents induced comparable numbers of chromosomal breaks in DSB-repair-deficient cells and wild-type cells.
- This indicates that chromosomal breaks can occur independently of DSB repair pathways.
- Cells deficient in replication completion factors (PIF1, ATRIP) showed increased breaks, suggesting unreplicated single-strand gaps contribute to break formation.
Conclusions:
- Chromosomal breaks are not exclusively caused by double-strand breaks (DSBs).
- Replication stress induced by specific agents can lead to chromosomal breaks through mechanisms independent of canonical DSB repair.
- Unreplicated single-strand gaps during DNA replication may be a source of mitotic chromosomal breaks.
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