Nuclear localization of selected centromeres and genes in irradiated leukemic cells
Fluorescence in situ hybridization (FISH) combined with high resolution cytometry were used for the determination of topographic characteristics of the centromeric heterochromatin (of the chromosomes 6, 8, 9, 17) and the tumor suppressor gene TP53 (which is located on the chromosome 17) in the human leukemic cell lines ML-1 and U937. The analyzed cells were either intact or irradiated by gamma rays and incubated for different time intervals.
The homologous centromeres and the TP53 genes were found closer to each other and also closer to the nuclear center 2 h after irradiation. These genetic elements recovered the initial status during the next 2-3 h . Statistical evaluation of our experimental results shows that the homologous centromeres and the homologous genes are positioned closer to each other 2 h after irradiation as a consequence of the fact that they are localized closer to the nuclear center (probably due to more pronounced decondensation of the chromatin related to repair). This radial movement of genetic loci, however, is not connected with DNA repair of double-strand breaks (DSB) by processes involving homologous recombination (HR), because the angular distribution of homologs remains random after irradiation.
P. Jirsová, E. Bártová, S. Kozubek, M. Kozubeka, E. Lukásová, A. Cafourková, E. A. Krasavinb, R. D. Govorunb, M. Skalníkováa, K. Buchnícková
Institute of Biophysics, Academy of Sciences of the Czech Republic,