The present study was undertaken to provide more information on the heterochromatin density in central and peripheral nuclear regions during “cell dedifferentiation“ represented by blastic transformation of mature T lymphocytes. Heterochromatin was visualized using a simple cytochemical method for the demonstration of DNA followed by computer-assisted densitometry of digitised images. The results indicated that the blastic transformation was accompanied by a marked and significant decrease in the heterochromatin density at the nuclear membrane. Thus, this nuclear peripheral region seems to be important not only for cell differentiation but also dedifferentiation events. It is also interesting that the non-stimulated resting mature cells in the present study were characterized by less condensed heterochromatin at the nuclear membrane than differentiated granulocytic or erythrocytic precursors and apoptotic myeloblasts or leukemic B lymphocytes described in the previous study. However, in contrast to these cells, resting and mature T lymphocytes in the present study are known to revert to cycling blastic cells after PHA treatment. In addition, it is also known that nuclear peripheral regions with heterochromatin represent sites of chromosomal attachments as well as “together crowded replicons“ and silent genes.

Institute of Hematology and Blood Transfusion Prague

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