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Updated: Jul 18, 2026
17:14
Chromosome Replicating Timing Combined with Fluorescent In situ Hybridization
Published on: December 10, 2012
Modulation of chromosome damage localization by DNA replication timing.
M V Di Tomaso1, W Martínez-López, G A Folle
1Department of Genetic Toxicology and Chromosome Pathology, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay. marvi@iibce.edu.uy
International Journal of Radiation Biology
|December 21, 2006
Summary
Chromosome breakpoint localization is influenced by DNA replication timing and chromatin remodeling. Early S-phase breakpoints occurred in euchromatin, while late S-phase breakpoints clustered in heterochromatin.
Area of Science:
- Cell Biology
- Genetics
- Molecular Biology
Background:
- Induced chromosome breakpoints (BP) non-randomly occur, suggesting factors influencing their localization.
- DNA synthesis and chromatin remodeling are hypothesized to play roles in BP distribution.
- The CHO9 X chromosome model presents distinct early-replicating euchromatin (Xpe) and late-replicating heterochromatin (Xqh).
Purpose of the Study:
- To investigate the influence of DNA replication and chromatin remodeling on BP distribution within euchromatin and heterochromatin.
- To utilize the CHO9 X chromosome as a model system for studying BP localization dynamics.
- To elucidate the relationship between replication timing and BP patterns.
Main Methods:
- Induced chromosome breakpoints using etoposide, ultraviolet-C light (UV-C), and methyl methanesulfonate (MMS).
- Incorporated 5-bromo-2'-deoxyuridine (BrdUrd) during specific S-phase stages to label early (Xpe) and late (Xqh) replicating regions.
- Mapped BP locations on CHO9 X chromosome arms using immunodetection in metaphase spreads.
Main Results:
- During early S-phase, etoposide and MMS-induced BP preferentially localized to the euchromatic Xpe arm.
- UV-C-induced BP showed random localization during early S-phase.
- During late S-phase, BP induced by all agents clustered in the heterochromatic Xqh arm.
Conclusions:
- Replication timing of euchromatin and heterochromatin significantly influences chromosome breakpoint localization.
- Chromatin remodeling processes are implicated in determining the non-random distribution of BP on the CHO9 X chromosome.
- The study provides insights into the mechanisms governing DNA damage and repair site distribution relative to replication dynamics.
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