DISTRIBUTION OF ABL AND BCR GENES IN CELL-NUCLEI OF NORMAL AND IRRADIATED LYMPHOCYTES

Using dual-color fluorescence in situ hybridization (FISH) combined wi th two-dimensional (2D) image analysis, the locations of ABL and BCR g enes in cell nuclei were studied, The center of nucleus-to-gene and mu tual distances of ABL and BCR genes in interphase nuclei of nonstimula ted and stimulated lymphocytes as well as in lymphocytes stimulated af ter irradiation were determined, We found that, after stimulation, the ABL and BCR genes move towards the membrane, their mutual distances i ncrease, and the shortest distance between heterologous ABL and BCR ge nes increases. The distribution of the shortest distances between ABL and BCR genes in the G(0) phase of lymphocytes corresponds to the theo retical distribution calculated by the Monte-Carlo simulation. Interes tingly, the shortest ABL-BCR distances in G(1) and S(G(2)) nuclei are greater in experiment as compared with theory. This result suggests th e 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 rando m 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 t han similar to 0.2 to 0.3 mu m). For comparison, we studied another pa ir 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 tha t in about 8% of lymphocytes, c-MYC and IgH are very close to each oth er. Similar results were obtained for human fibroblasts. gamma-Radiati on leads to substantial changes in the chromatin structure of stimulat ed lymphocytes: ABL and BCR genes are shifted to the nuclear center, a nd mutual ABL-BCR distances become much shorter in the G(1) and S(G(2) ) nuclei, Therefore, we hypothesize that the changes of chromatin stru cture 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 loc ated close together in a certain fraction of cells substantiates the h ypothesis that physical distance plays an important role in the proces ses leading to the translocations that are respon sible for oncogenic transformation of cells. (C) 1997 by The American Society of Hematolog y.