Electron Microscope and High Resolution Autoradiographic Studies of Megaloblastic Erythropoiesis

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Abstract
Bone marrow fragments from 10 patients with a megaloblastic anemia due to vitamin B12 or folate deficiency were studied by EM and electron microscope autoradiography. A proportion of the erythroblasts showed ultrastructural abnormalities. Some of the cells containing autophagic vacuoles, large siderosomes, Fe-laden mitochondria, irregularly shaped nuclei, membrane-bound nuclear clefts or incomplete nuclear membranes were capable of DNA, RNA and protein synthesis. Other cells showed advanced degenerative changes, e.g., the distension of the perinuclear space, the clumping of cytoplasmic organelles near the nucleus and a reduction in the electron density and ribosome content of the cytoplasm. Most of these grossly abnormal cells suffered from either a marked depression or an arrest in protein and RNA synthesis, and were presumably destined for phagocytosis by reticulum cells.