The present study was undertaken to provide more information on the density and distribution of heterochromatin in early and advanced stages of the granulocytic, lymphocytic and erythroid development. Heterochromatin was visualized using a simple cytochemical method for the demonstration of DNA followed by computer-assisted densitometry of the digitized images. The largest heterochromatin density in early proliferating stages of all studied blood cell lineages was noted in the perinucleolar region and centrally located chromocentres. In contrast, the heterochromatin density at the nuclear membrane was significantly lower. In advanced nonproliferating stages or apoptotic cells the heterochromatin density increased and was similar in all nuclear regions, i.e. in the perinucleolar regions, chromocentres, and at the nuclear membrane. Thus, such observations indicated that the heterochromatin condensation in the perinucleolar region and chromocentres, i.e. in "gene-rich nuclear regions", of differentiating and maturing progenitors of blood cells preceded that at the nuclear periphery.

Institute of Haematology and Blood Transfusion Prague

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