Modulation of chromosome damage localization by DNA replication timing.
OBJECTIVE
Non-random occurrence of induced chromosome breakpoints (BP) has been repeatedly reported. DNA synthesis and chromatin remodeling may influence chromosome BP localization. The CHO9 X chromosome exhibits an early replicating short euchromatic arm (Xpe) and a late replicating long heterochromatic arm (Xqh). We investigated the role played by DNA replication and related chromatin remodeling processes on BP distribution in eu/heterochromatin using the CHO9 X chromosome as a model.


METHODS
BP induced by etoposide, a topoisomerase II inhibitor, as well as by the S-dependent clastogens ultraviolet-C light (UV-C) and methyl methanesulfonate (MMS) were mapped to CHO9 X chromosome arms. The base analogue 5-bromo-2'-deoxyuridine (BrdUrd) was pulse-added immediately after UV-C irradiation or during etoposide and MMS treatments (40 min) to identify cells in early S-phase (Xpe labeled) or late S-phase (Xqh labeled) after indirect BrdUrd immunodetection in metaphase spreads using primary anti-BrdUrd and secondary fluorochrome-tagged antibodies.


RESULTS
During early S-phase, BP induced by etoposide and MMS mapped preferentially to Xpe while BP produced by UV-C localized randomly. BP induced by all agents during late S-phase clustered in Xqh.


CONCLUSIONS
Results obtained suggest that replication time of eu/heterochromatin as well as chromatin remodeling may determine BP localization on the CHO9 X chromosome.
Di Tomaso
M V
MV
Department of Genetic Toxicology and Chromosome Pathology, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay. marvi@iibce.edu.uy
Martínez-López
W
W
Folle
G A
GA
Palitti
F
F
D000818:Animals; D016466:CHO Cells; D002869:Chromosome Aberrations / Q000528:radiation effects*; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage / Q000235:genetics*; D004261:DNA Replication / Q000502:physiology* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D011829:Radiation Dosage; D014960:X Chromosome / Q000235:genetics* / Q000528:radiation effects*