Studies on the DNA metabolism of erythroid cell. II. Decrease in DNA contents and DNA synthetic rate during erythroid cell specialization

For the purpo3e to determine exactly what stage of cell specialization the DNA level of erythroid cell nuclei begins to decline, the author observed the DNA level of erythroblasts in mitosis by microspectrophotometry and the DNA synthesis by flash labeling with H3-thymidine. The cell samples were obtained from the bone marrow of normal, blood-depleted and phenylhydrazine-treated animals, and the anemic animals received a mass red cell transfusion, all the animals being injected with colchicine 4 hours before obtaining the bone marrow sample. DNA level was measured on the smeared cells stained by Feulgen reaction and DNA synthesis by autoradiography on the smeared cells. Besides these, chromosome number was observed on the anemic rat erythroblasts at metaphase by air dry method. The observations indicated that the DNA level begins to decrease at polychromatic stage being accompanied by a decrease in TDH3-incorporation into DNA, reaching minimum level at orthochromatic cell both in DNA contents and synthesis. Chromosome numbers of erythroblasts of rat were irregular being distri buted between 42 to 20. The data have suggested that the DNA level of erythroblasts decreases only in the later stages of cell specialization, and at polychromatic stage the chromosome number may also decrease in rabbit at polychromatic stage by the cell division with an incomplete DNA replication. The high DNA level of the erythroblasts of rabbit, in severe anemia where most of the cells are denucleated at polychromatic and late basophilic stages, has been discussed from the view point of the insufficient DNA replication at polychromatic stages.