Nucleolar organizer regions in normal hematopoiesis: relationship to cellular proliferation and maturation

The pattern of nucleolar organizer regions (NORs) in normal interphase hematopoietic cells was studied employing the Ag-NOR technique in bone marrow smears. A characteristic pattern of clusters and dots was observed for each cell type. The presence of clusters correlated with cells in proliferation, while in non-proliferating cells only dots were seen. In granulopoiesis, as in erythropoiesis, the number of clusters was highest in the most immature cells, decreasing as maturation took place. Conversely, the number of dots was lowest in the most immature cells, increasing with maturation. In the mature endstage cells, only few dots were seen. The results justify separate counting of clusters and dots, which probably represent different physiologic activities. The present study offers basic data for the study of benign and malignant hematologic disorders where alterations of cellular proliferation and/or maturation occur.