An ultrastructural study of erythropoietin-induced red cell formation in mouse spleen

Abstract

An electron microscopic study was made of the wave of red cell formation induced by erythropoietin in the spleens of hypoxia-induced polycythemic mice, initially exhibiting markedly inhibited erythropoiesis. The spleens of control polycythemic mice are devoid of developing erythroid elements. At 12–24 hours after erythropoietin injection, only proerythroblasts are noted in the spleens. Proerythroblasts are replaced by basophilic, polychromatophilic, and orthochromatic erythroblasts and reticulocytes at 48 hours; orthochromatic erythroblasts and reticulocytes predominated at 72 hours. Cells of the erythroid series are distinguished mainly by their chromatin arrangement. Chromatin clumps begin to form in the basophilic erythroblast, are most prominent in the polychromatophilic erythroblast, and become increasingly inconspicuous in the orthochromatic erythroblast until finally the chromatin is uniformly distributed in the nucleus about to be extruded. A description is given of the process of nuclear extrusion and the phagocytosis of the nuclei by macrophages. In all stages of development, the erythroid cells occur in clusters. This arrangement may facilitate the distribution, from centrally located macrophagocytic “nurse” cells, of ferritin and other materials essential for the processes of development.