Many types of cells with very different functions are found in human blood. White blood cells, so called leukocytes, were studied in our experiments. Particularly granulocytes and the cells of the granulocytic pathway of differentiation were in the scope of our interest.

We have investigated the nuclear topography of human granulocytes with a characteristic lobular shape of nuclei. The nuclear position of centromeric heterochromatin, the nuclear location of all chromosomes and the topography of genes like ABL, BCR, C-MYC and p53 were determined using fluorescence in situ hybridisation (FISH). The nuclear positioning of the mentioned genetic structures was detected in human granulocytes (differentiation in vivo) and compared with the location of these genetic structures in human leukemic promyelocytes HL-60 undergoing granulocytic differentiation in vitrothat was induced using retinoic acid. HL-60 promyelocytes were also used as an undifferentiated population.

In the human granulocytes we found some chromosomes positioned in the inner part of cell nucleus (chromosomes 17, 19, 21, 22) and the others were located closer to the nuclear membrane (chromosomes 3, 6 and 16). The ABL, BCR and p53 genes were located more centrally than the more peripherally positioned C-MYC genes. The same peripheral location was detected in the centromeric sequences of chromosomes 2, 7, 8, 9, 17 and X in comparison with undifferentiated HL-60 cells.

In our experiments we found five topographic types of chromatin structures, in the case when granulocytic nuclei were divided in two parts, according the nuclear weight centre. Our studies contribute to the knowledge of the high order chromatin structure of segmented granulocytes whose chromatin arrangement can be an important aspect of their function in the immunity system.