DNA Dynamics in Rat Granulopoiesis studied by Cytophotometry

THE theory that the DNA content of cells remains constant has been widely accepted, but some workers1–3 presume that DNA content decreases either during the mitosis of the precursor cell (hypoploidy4, haploidy5) or during the interphase maturation of the myelocyte stage into the granulocyte stage. Another open question is: which myeloid cells are capable of DNA synthesis and mitosis? Most authors express the belief that these are the myeloblasts, promyelocytes and myelocytes6,7. Recent evidence, however, indicates that some metamyelocytes can synthesize DNA. This has been shown in the bone marrow of the guinea-pig after haemorrhage, by labelling with 3H-thymidine and by cytophotometry8; in irradiated rats as well as normal rats, by autoradiographic methods9; and in humans, by cinematomicrography10.