title: Interference in DNA replication can cause mitotic chromosomal breakage unassociated with double-strand breaks.
abstract: Morphological analysis of mitotic chromosomes is used to detect mutagenic chemical compounds and to estimate the dose of ionizing radiation to be administered. It has long been believed that chromosomal breaks are always associated with double-strand breaks (DSBs). We here provide compelling evidence against this canonical theory. We employed a genetic approach using two cell lines, chicken DT40 and human Nalm-6. We measured the number of chromosomal breaks induced by three replication-blocking agents (aphidicolin, 5-fluorouracil, and hydroxyurea) in DSB-repair-proficient wild-type cells and cells deficient in both homologous recombination and nonhomologous end-joining (the two major DSB-repair pathways). Exposure of cells to the three replication-blocking agents for at least two cell cycles resulted in comparable numbers of chromosomal breaks for RAD54(-/-/)KU70(-/-) DT40 clones and wild-type cells. Likewise, the numbers of chromosomal breaks induced in RAD54(-/-/)LIG4(-/-) Nalm-6 clones and wild-type cells were also comparable. These data indicate that the replication-blocking agents can cause chromosomal breaks unassociated with DSBs. In contrast with DSB-repair-deficient cells, chicken DT40 cells deficient in PIF1 or ATRIP, which molecules contribute to the completion of DNA replication, displayed higher numbers of mitotic chromosomal breaks induced by aphidicolin than did wild-type cells, suggesting that single-strand gaps left unreplicated may result in mitotic chromosomal breaks.
authors.affiliation: Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshidakonoe, Sakyo-ku, Kyoto, Japan.
authors.forename: Mari
authors.initials: M
authors.lastname: Fujita
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sasanuma
authors.forename: Kimiyo N
authors.initials: KN
authors.lastname: Yamamoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Harada
authors.forename: Aya
authors.initials: A
authors.lastname: Kurosawa
authors.forename: Noritaka
authors.initials: N
authors.lastname: Adachi
authors.forename: Masato
authors.initials: M
authors.lastname: Omura
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
authors.forename: Shunichi
authors.initials: S
authors.lastname: Takeda
authors.forename: Kouji
authors.initials: K
authors.lastname: Hirota
mesh_terms: D000818:Animals; D034961:Antigens, Nuclear / Q000235:genetics; D016590:Aphidicolin / Q000494:pharmacology; D017209:Apoptosis; D045744:Cell Line, Tumor; D002645:Chickens; D019457:Chromosome Breakage; D053903:DNA Breaks, Double-Stranded; D004265:DNA Helicases / Q000502:physiology; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000502:physiology; D004261:DNA Replication / Q000187:drug effects*; D004268:DNA-Binding Proteins / Q000235:genetics; D005472:Fluorouracil / Q000494:pharmacology; D055786:Gene Knockout Techniques; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology; D000072200:Ku Autoantigen; D008938:Mitosis
chemical_list: D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D016590:Aphidicolin; D004265:DNA Helicases; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen; D045643:DNA Repair Enzymes; D005472:Fluorouracil; D006918:Hydroxyurea