Frequences of Chromosomal Exchanges Induced with Ionising Radiation Reflect Chromosome Arrangement in the Cell Nucleus
DNA double-strand breaks produced by ionising radiation are often misrejoined to cause chromosome exchange aberrations. We show in this study that the frequencies of exchange aberrations between selected chromosomes induced with fast neutrons and gamma rays give an insight into the arrangement of chromosomes within the cell nucleus during interphase. The newly elaborated software enabled us to define stage positions of mitosis on a slide and automatic scan of images according to these positions after repeated hybridisation. In each hybridisation two different pairs of chromosomes were stained. Comparing the images of the same mitosis after five repeated hybridisations in which two different pairs of chromosomes were distinguished from remaining chromosomes, interchanges among 10 selected chromosomes were detected. It was found that the frequency of exchanges was not linearly proportional to the DNA content of interacting chromosomes especially in cells irradiated with neutrons. Significantly higher frequencies of interchanges were observed only between some pairs of chromosomes. Owing to the confinement of individual chromosomes within a small subregions of the nucleus where the chromatin undergoes only diffusive motion, the vicinity of chromosomal territories could be very important in mutual interaction and exchange of genetic material. One radiation track of densely ionising radiation can induce dsb in the boundary of two neighbouring chromosomes in mutual proximity. The proximity of these damages facilitates their interaction and misrejoining. The higher frequency of interchanges between some chromosomes after irradiation with ionising radiation indicates the proximity of interacting chromosomes in interphase nucleus. The proximity of subregions of specific chromosomes in the cell nucleus can be one of the reasons giving rise to malignant translocations.
Lukasova E, Kozubek S, Kozubek M1, Cafourkova A, Koutna I1, Skalnikova M1,Bártová E, Jirsová P
Institute of Biophysics, AS CR,