Are microproerythroblasts in human bone marrow real or artefacts? A cytochemical note

A short cytochemical note on the nucleolar and cytoplasmic RNA concentration in differentiating cells represented by human erythroblasts

The present study was undertaken to provide more information on the nucleolar and cytoplasmic RNA concentration in differentiating cells of the erythroid lineage. These cells represent a convenient model to study cell differentiation since all stages are morphologically well characterised. The bone marrow of patients suffering from the chronic phase of chronic myeloid leukaemia without a large increase in the granulocyte to erythroid ratio provided erythroblasts for computer-assisted image density measurements of RNA in nucleoli and cytoplasm at the single cell level. The measurements indicated a significant decrease of the nucleolar and cytoplasmic RNA concentration only in advanced stages of erythroblast differentiation (polychromatic and orthochromatic erythroblasts). The ratio of the nucleolar to cytoplasmic RNA concentration was otherwise very stable and did not change during differentiation, being similar in the early and advanced stages of erythroblastic development. In contrast, the nucleolar size significantly decreased even during the early stages of erythroid development (basophilic erythroblasts). This marked decrease in the nucleolar diameter in differentiating erythroblasts and the less marked decrease in the nucleolar RNA concentration suggest that the amount of RNA in the nucleolus is closely associated with nucleolar size rather than on its concentration within the nucleolar body.

A short note on the nuclear diameter in human early granulocytic progenitors

The information on the nuclear size in early granulocytic progenitors is very limited. Numerical data on the nuclear diameter and size in these cells are missing in the literature. Therefore the nuclei of myeloblasts and promyelocytic cells were measured in bone marrow smears of patients suffering from chronic phase of chronic myeloid leukaemia since the general morphology of granulocytic progenitors is very similar to those in non-leukemic persons. Moreover, the increased granulopoiesisinthese patients provided a satisfactory number of early granulocytic progenitors for karyometric measurements. Nuclear diameter in digitised and processed images of these cells was measured directly on the monitor screen at magnification 4300x using a computerised photoprogram. The nuclear mean diameter in both myeloblasts and promyelocytes ranged between 11 and 13 microm. Cells with smaller or larger nuclei were observed less frequently. Since the nuclear size depends on the cell cycle stage, a possibility exists that both granulocytic progenitors are mostly in the S and less frequently in G1 or G2 phase. Thus, the mean nuclear diameter, i.e. nuclear size, might be useful in helping to estimate the cell cycle stage of these cells in bone marrow smears at the single cell level. In addition, the results of the present study also indicated that the nuclear diameter in myeloblasts as well as promyelocytes of studied patients was not substantially influenced by the cytostatic therapy with imatinib mesylate.