Effectiveness of 0.28 keV carbon K ultrasoft X-rays at producing simple and complex chromosome exchanges in human fibroblasts in vitro detected using FISH.
OBJECTIVE
To study the effects of carbon K ultrasoft X-rays, which produce a single photoelectron with a track length of < 7 nm, on the production of structural chromosome-type changes.


METHODS
Untransformed human fibroblasts (HF12) were irradiated in G1 phase. Aberrations were analysed using fluorescence in situ hybridization using multi-coloured chromosome specific DNA probes for chromosomes 1 and 2 and an alpha-satellite pan-centromeric probe.


RESULTS
CK X-rays have a high efficiency per unit absorbed dose for producing simple and complex exchanges. Mean absorbed doses of 0.33-1.31 Gy produce simple exchanges with a predominantly linear dose dependency, and visibly complex exchanges increased by more than the power 2 of the dose, with no evidence of a linear component. The proportion of exchanges that are visibly complex ranged from 9% to 46%.


CONCLUSIONS
The linear response for simple exchanges provides further support to the hypothesis that damaged DNA may be able to interact with undamaged DNA. The high proportion of complex exchanges may be due to the increased efficiency of double-strand break induction and to the high density of tracks per unit absorbed dose targeting pre-existing sites, some of which may be close to the incident nuclear membrane.
MRC Radiation and Genome Stability Unit, Harwell, Oxon, UK.
C S
CS
Griffin
M A
MA
Hill
D G
DG
Papworth
K M
KM
Townsend
J R
JR
Savage
D T
DT
Goodhead
D002460:Cell Line; D002503:Centromere / Q000528:radiation effects; D002869:Chromosome Aberrations; D002878:Chromosomes, Human, Pair 1 / Q000528:radiation effects*; D002889:Chromosomes, Human, Pair 2 / Q000528:radiation effects*; D015342:DNA Probes; D004276:DNA, Satellite / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000528:radiation effects; D006801:Humans; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D014965:X-Rays
D015342:DNA Probes; D004276:DNA, Satellite