Studies on reticuloendothelial system and hemato-poiesis, III. Relationship between differentiation of erythroblast and oxygen tension

For the purpose to clarify the control mechanism of erythroid cell differentiation, the author observed morphologic changes in bone-marrow cells and circulating red cells in phenylhydrazine anemia of rabbits by introducing a mass of red cells into vein at one time and reached the following conclusions. 1. After red cell transfusion in a mass to animal showing a marked hematopoietic activity, anisocytosis or macrocytosis becomes distinct with the appearance of big reticulocytes and red cells as large as four times the normal in volume. This suggests, judging from their volume, the accelerated denucleation of erythroblast as early as at the late basophilic stage. 2. Observations on bone marrow at this stage revealed the reduction in the number of erythroblasts of undifferentiated type with the increase of rather differentiated ones. In erythroid islet, undifferentiated cells are found surrounding a reticulum cell located in the center, while well differentiated ones in the outskirt area are situated near the sinusoid. Such a cell arrangement suggests that the erythroid cell requires a high oxygen tension for its differentiation. 3. From these observations and other results obtained from the studies on reticulocyte maturation and RNA synthesis of erythroblast, the author stresses that erythroid cells can differentiate as long as it is provided with a certain level of oxygen, even though it may develop m-RNA for differentiation. In other words, there should be two steps in the differentiation of erythroblast, the first is m-RNA synthesis induced by the information and the second is the somatic protein synthesis with oxygen supply. This seems to be directly connected to the control mechanism of hematopoiesis by oxygen.