title: A comparison of G2 phase radiation-induced chromatid break kinetics using calyculin-PCC with those obtained using colcemid block.
abstract: To study the possible influence of cell-cycle delay on cells reaching mitosis during conventional radiation-induced chromatid break experiments using colcemid as a blocking agent, we have compared the chromatid break kinetics following a single dose of gamma rays (0.75 Gy) in metaphase CHO cells using calyculin-induced premature chromosome condensation (PCC), with those using colcemid block. Calyculin-induced PCC causes very rapid condensation of G2 cell chromosomes without the need for a cell to progress to mitosis, hence eliminating any effect of cell-cycle checkpoint on chromatid break frequency. We found that the kinetics of the exponential first-order decrease in chromatid breaks with time after irradiation was similar (not significantly different) between the two methods of chromosome condensation. However, use of the calyculin-PCC technique resulted in a slightly increased rate of disappearance of chromatid breaks and thus higher frequencies of breaks at 1.5 and 2.5 h following irradiation. We also report on the effect of the nucleoside analogue ara A on chromatid break kinetics using the two chromosome condensation techniques. Ara A treatment of cells abrogated the decrease in chromatid breaks with time, both using the calyculin-PCC and colcemid methods. We conclude that cell-cycle delay may be a factor determining the absolute frequency of chromatid breaks at various times following irradiation of cells in G2 phase but that the first-order disappearance of chromatid breaks with time and its abrogation by ara A are not significantly influenced by the G2 checkpoint.
authors.affiliation: Bute Medical School, University of St Andrews, St Andrews KY16 9TS, UK. peb@st-and.ac.uk
authors.forename: Peter E
authors.initials: PE
authors.lastname: Bryant
authors.forename: Hossein
authors.initials: H
authors.lastname: Mozdarani
mesh_terms: D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D001681:Biological Assay; D002273:Carcinogens / Q000494:pharmacology*; D002460:Cell Line; D002842:Chromatids / Q000187:drug effects / Q000528:radiation effects*; D019457:Chromosome Breakage; D006224:Cricetinae; D053903:DNA Breaks, Double-Stranded; D003703:Demecolcine / Q000494:pharmacology*; D016195:G2 Phase / Q000187:drug effects / Q000528:radiation effects*; D005720:Gamma Rays; D007700:Kinetics; D008387:Marine Toxins; D010080:Oxazoles / Q000494:pharmacology*; D014740:Vidarabine / Q000494:pharmacology
chemical_list: D000963:Antimetabolites; D002273:Carcinogens; D008387:Marine Toxins; D010080:Oxazoles; C059041:calyculin A; D014740:Vidarabine; D003703:Demecolcine