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Chromosome healing in mouse embryonic stem cells.
C N Sprung1, G E Reynolds, M Jasin
1Radiation Oncology Research Laboratory, University of California, San Francisco, 1855 Folsom Street, MCB 200, San Francisco, CA 94103, USA.
Summary
Chromosome healing, the addition of telomeres to broken chromosomes, is a newly identified repair mechanism in mammalian cells. This process involves specific telomere sequence additions at double-strand break sites.
Area of Science:
- Genetics
- Molecular Biology
- Cell Biology
Background:
- Chromosome healing, the addition of new telomeres to broken chromosome ends, is well-documented in unicellular organisms.
- Its role in mammalian cells responding to DNA double-strand breaks remained largely unknown.
Purpose of the Study:
- To investigate the mechanism and role of chromosome healing in mammalian cells.
- To establish a system for analyzing chromosome healing in mouse embryonic stem cells.
Main Methods:
- Developed a system in mouse embryonic stem cells with a marked telomere containing selectable markers and an I-SceI recognition site.
- Induced double-strand breaks using I-SceI endonuclease expression.
- Analyzed telomere addition sites and characteristics using selection markers.
Main Results:
- Transient I-SceI expression induced terminal deletions with telomeric repeat additions at broken chromosome ends.
- New telomere additions occurred at sites with complementarity to telomeric repeats, often at the ATAA overhang.
- Added telomeres were shorter than parental telomeres and often elongated over time in culture.
Conclusions:
- Chromosome healing is a functional DNA repair mechanism for double-strand breaks in mammalian cells.
- The process involves specific sequence-dependent addition of telomeric repeats.
- This study provides the first evidence of chromosome healing in mammalian cells.