Chromatid break rejoining and exchange aberration formation following gamma-ray exposure: analysis in G2 human fibroblasts by chemically induced premature chromosome condensation.
OBJECTIVE
To analyse the kinetics of chromatid break induction, rejoining, and misrejoining after y-irradiation in G2 phase human cells using premature chromosome condensation induced by calyculin A.


METHODS
Human fibroblast AG1522 cells were irradiated with gamma-rays and chromosomes were then prematurely condensed by calyculin A. The number of chromatid breaks and chromatid exchanges in G2 chromosomes were scored, and fitted curves were calculated.


RESULTS
Calyculin A induced premature chromosome condensation in cells immediately after irradiation. Kinetics of rejoining of chromatid breaks demonstrated two exponential components with rapid and slow time constants. Within 5 min after irradiation, the number of chromatid breaks fell rapidly to about one-half, then gradually decreased. Chromatid exchanges were formed very quickly, reaching a plateau within 20 min from exposure.


CONCLUSIONS
Chemically induced premature chromosome condensation technique allows a simple, rapid and precise analysis of chromatid breakage and rejoining. The rapid kinetic component was particularly well characterized.
Gotoh
E
E
Division of Genetic Resources, National Institute of Infectious Diseases, Tokyo, Japan. egotoh@nih.go.jp
Kawata
T
T
Durante
M
M
D002478:Cells, Cultured; D002842:Chromatids / Q000528:radiation effects*; D002869:Chromosome Aberrations; D004260:DNA Repair; D005347:Fibroblasts / Q000528:radiation effects; D016195:G2 Phase / Q000528:radiation effects*; D005720:Gamma Rays; D006801:Humans