Induction and persistence of chromosomal exchanges in mouse bone marrow cells following whole-body exposure to X-rays.
OBJECTIVE
To investigate the induction and persistence of chromosome aberrations in mouse bone marrow cells after X-ray exposure and to detect differential involvement of individual chromosomes in translocations.


METHODS
Male and female Swiss mice were exposed to 1 and 3 Gy of X-rays. Chromosome aberrations in bone marrow cells were analysed at 1, 7, 21 and 100 days following irradiation by means of fluorescence in situ hybridization (FISH) with mouse chromosome-specific DNA libraries (#1,13; #2,8; #6,15 and X,Y). In total, 38% of mouse genome was painted and examined.


RESULTS
Pooled data indicate that the frequencies of dicentrics and fragments decreased with time and reached to the control level at day 21 after exposure. Following exposure to 1 Gy of X-rays, the frequencies of translocations were not significantly lower between days 7 and 100 than observed at day 1. However, the frequencies of translocations for the 3 Gy group were significantly (about 40%) lower at day 7, then remained constant up to day 100. After exposure to 3Gy of X-rays, the frequencies of non-reciprocal translocations decreased with time, whereas reciprocal translocations between days 7 and 100 were not significantly less frequent than at day 1. A comparison of observed and expected numbers of translocations involving individual chromosomes showed that at day 1 after irradiation, distribution of X-ray-induced translocations among the painted chromosomes was proportional to their DNA content. However, at day 100 after exposure, the observed translocations involving chromosome 2 were more frequent than expected, those involving chromosomes 8 and 15 were less frequent than expected, while chromosomes 1, 6, X and Y were involved as frequently as expected.


CONCLUSIONS
Among induced translocations, non-reciprocal translocations are relatively unstable, especially after exposure to high-dose X-rays. While the initial distribution of X-ray-induced translocations is proportional among the painted chromosomes, the persistence of these translocations is heterogeneous.
Xiao
Y
Y
Department of Radiation Genetics and Chemical Mutagenesis, Leiden University Medical Centre, The Netherlands.
Darroudi
F
F
Grigorova
M
M
Natarajan
A T
AT
D000782:Aneuploidy; D000818:Animals; D001854:Bone Marrow Cells / Q000528:radiation effects*; D002869:Chromosome Aberrations; D005260:Female; D008297:Male; D051379:Mice; D014178:Translocation, Genetic; D014916:Whole-Body Irradiation; D014965:X-Rays