Repair and misrepair of heavy-ion-induced chromosomal damage.
The premature chromosome condensation (PCC) technique was used to investigate chromosomal damage, repair, and misrepair in the G phase of a human/hamster hybrid cell line that contains a single human chromosome. Plateau-phase cell cultures were exposed to either x-rays or a 425 MeV/u beam of neon ions near the Bragg peak where the LET is 183 kev/micrometers. An in situ hybridization technique coupled to fluorescent staining of PCC spreads confirmed the linearity of the dose response for initial chromatin breakage in the human chromosome to high doses (1600 cGy x-ray or 1062 cGy Ne). On Giemsa-stained slides, initial chromatin breakage in the total genome and the rejoining kinetics of these breaks were determined. As a measure of chromosomal misrepair, ring PCC aberrations were also scored. Ne ions were about 1.5 x more effective per unit dose compared to x-rays at producing the initially measured chromatin breakage. 90% of the x-ray-induced breaks rejoined in cells incubated at 37 degrees C after exposure.  In contrast, only 50% of Ne-ion-induced breaks rejoined.  In the irradiated G1 cells, ring PCC aberrations increased with time apparently by first order kinetics after either x-ray or Ne exposures. However, far fewer rings formed in Ne-irradiated cells after a dose giving a comparable initial number of chromatin breaks. Following x-ray exposures, the yield of rings formed after long repair times (6 to 9 hrs) fit a quadratic dose-response curve. These results indicate quantitative and qualitative differences in the chromosomal lesions induced by low- and high-LET radiations.
Goodwin
E
E
Cell and Molecular Biology Division, Lawrence Berkeley Laboratory, University of California, Berkeley 94720, USA.
Blakely
E
E
Ivery
G
G
Tobias
C
C
D000818:Animals; D002470:Cell Survival; D002843:Chromatin / Q000528:radiation effects*; D002869:Chromosome Aberrations; D002889:Chromosomes, Human, Pair 2 / Q000528:radiation effects; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D020450:Heavy Ions; D006801:Humans; D006822:Hybrid Cells / Q000528:radiation effects; D007399:Interphase; D007700:Kinetics; D009356:Neon; D014965:X-Rays
D002843:Chromatin; D009356:Neon