Effects of colchicine on the enucleation of erythroid cells and macrophages in the liver of mouse embryos: ultrastructural and three-dimensional studies.

Enucleation is the last event in the development of a definitive erythroid line, and extruded nuclei are phagocytosed by macrophages. Both colchicine and cytochalasin have been known to exert a great influence on the enucleation process, but the relationship between enucleation and these agents has not yet been clearly revealed in vivo. Our aim was to clarify the significance of the enucleation in liver erythropoiesis and macrophage phagocytosis by colchicine and cytochalasin administration to embryonic mice. Pregnant mice were intraperitoneally injected with colchicine or cytochalasin at 13 days of gestation. Embryonic livers were removed at intervals of 3, 6 and 12 h after injection for processing for light and electron microscopy, and, to obtain three-dimensional morphology of erythroids at enucleation, computer-aided reconstructions were performed by light microscopy. Colchicine injections had cytolytic effects on hepatocytes and macrophages, and numerous erythroblasts were observed in the process of enucleation after colchicine injection. However, the extruding nuclei were irregularly shaped, and some erythroblasts at mitosis showed extreme peripheralization of their chromosomal masses and cell membrane constriction. Enucleation behavior could also be observed in immature erythroblasts. Liver macrophages engulfed extruded nuclei and erythroblasts in mitosis. Cytochalasin injections, on the other hand, had no significant effect on embryonic livers. The progress of erythroblast mitosis was clearly stopped by colchicine injection, and numerous erythroblasts at mitosis were extruding their nuclear compartment. Following colchicine injection, erythroid enucleation also took place in immature erythroblasts, and mitotic erythroids were phagocytosed. In enucleation, more attention should be paid to hematopoietic environmental factors than to hemopoietic cell factors.