Perinucleolar heterochromatin during the cell differentiation using human leukemic neutrophils as a convenient model

• The increasing size of the perinucleolar heterochromatin with silent genes in differentiating leukemic cells in both untreated and treated patients with specific therapy apparently reflects the genomic stability in this nuclear region during the cell differentiation.
• The specific anti-leukemic treatment induced an increased perinucleolar heterochromatin condensation in differentiating leukemic cells and represents the “premature” terminal differentiation.

The perinucleolar region represents a special nuclear compartment involved in the cell malignancy and the perinucleolar heterochromatin reflects the presence of silent genes. The present study was undertaken to provide complementary and missing information on the perinucleolar heterochromatin in differentiating neutrophils in the bone marrow of patients with the chronic myeloid leukemia. That lineage is a very convenient model because of the increased number of granulocytic precursors that is satisfactory for size as well as optical density measurements in single cells. Moreover, the differentiation stages of neutrophils are well defined and easily identified. According to diameter measurements the enlarged width of the perinucleolar heterochromatin shell accompanied the decreasing nucleolar size in advanced stages of the cell differentiation. Such trend was not influenced by the anti-leukemic therapy with imatinib. Thus the increasing size of the perinucleolar heterochromatin shell with silent genes might reflect the genomic stability of the perinucleolar region during the cell differentiation. On the other hand, the increased perinucleolar heterochromatin condensation after the specific anti-leukemic therapy with imatinib indicated a “premature terminal differentiation” of leukemic neutrophils.