Distribution of ABL and BCR genes in cell nuclei of normal and irradiated lymphocytes

Using dual-color fluorescence in situ hybridization (FISH) combined with two-dimensional (2D) image analysis, the locations of ABL and BCR genes in cell nuclei were studied, The center of nucleus-to-gene and mutual distances of ABL and BCR genes in interphase nuclei of nonstimulated and stimulated lymphocytes as well as in lymphocytes stimulated after irradiation were determined, We found that, after stimulation, the ABL and BCR genes move towards the membrane, their mutual distances increase, and the shortest distance between heterologous ABL and BCR genes increases. The distribution of the shortest distances between ABL and BCR genes in the G(0) phase of lymphocytes corresponds to the theoretical distribution calculated by the Monte-Carlo simulation. Interestingly, the shortest ABL-BCR distances in G(1) and S(G(2)) nuclei are greater in experiment as compared with theory. This result suggests the existence of a certain regularity in the gene arrangement in the G(1) and S(G(2)) nuclei that keeps ABL and BCR genes at longer than random distances. On the other hand, in about 2% to 8% of lymphocytes, the ABL and BCR genes are very close to each other (the distance is less than similar to 0.2 to 0.3 mu m). For comparison, we studied another pair of genes, c-MYC and IgH, that are critical for the induction of t(8;14) translocation that occurs in the Burkitt's lymphoma, We found that in about 8% of lymphocytes, c-MYC and IgH are very close to each other. Similar results were obtained for human fibroblasts. gamma-Radiation leads to substantial changes in the chromatin structure of stimulated lymphocytes: ABL and BCR genes are shifted to the nuclear center, and mutual ABL-BCR distances become much shorter in the G(1) and S(G(2)) nuclei, Therefore, we hypothesize that the changes of chromatin structure in the irradiated lymphocytes might increase the probability of a translocation during G(1) and S(G(2)) stages of the cell cycle. The fact that the genes involved in the t(8;14) translocation are also located close together in a certain fraction of cells substantiates the hypothesis that physical distance plays an important role in the processes leading to the translocations that are respon sible for oncogenic transformation of cells. (C) 1997 by The American Society of Hematology.