Heterochromatin density (condensation) during cell differentiation and maturation using the human granulocytic lineage of chronic myeloid leukaemia as a convenient model.

The present study was undertaken to provide complementary data on the heterochromatin condensation in both central and peripheral nuclear regions during the cell differentiation and maturation using computer-assisted density measurements at the single-cell level. The lineage of neutrophilic granulocytes in the bone marrow of patients suffering from chronic myeloid leukaemia was very convenient for such study because the increased number of granulocytes in all developmental stages was satisfactory for heterochromatin density measurements. The morphology of leukaemic and non-leukaemic neutrophilic granulocytes is similar and each differentiation or maturation stage is easily identified. A markedly increasing heterochromatin density--condensation--in the peripheral nuclear region at the nuclear envelope accompanied both the differentiation and maturation of these cells. Thus, peripheral chromosomal territories at the nuclear envelope are important for both the differentiation and maturation process. In contrast, the heterochromatin density of nuclear central regions was already high in early differentiation stages and exhibited a less distinct increase during the differentiation, but was more apparent in late maturation stages representing the terminal differentiation. A limited number of maturing cells with persisting large heterochromatin density in central nuclear regions without markedly increased heterochromatin condensation at the nuclear periphery might represent a further maturation abnormality--asynchrony--during the granulocytic development. From the methodological point of view, both, the cytochemical method for the DNA demonstration and the panoptic May-Grünwald-Giemsa staining, are convenient for computer-assisted chromatin densitometry at the single-cell level.