DISTRIBUTION OF ACTIN, MYOSIN, AND SPECTRIN DURING ENUCLEATION IN ERYTHROID-CELLS OF HAMSTER-EMBRYO

Yolk-sac derived erythroblasts undergo semi-synchronous maturation and some of them enucleate in the peripheral. blood of embryos. We have s tudied the assembly and distribution of actin, myosin, and spectrin du ring the enucleation of Syrian hamster embryonic erythroblasts. At day 11 of the gestation, that is just before the start of the enucleation , formation of a cytoskeletal structure consisted chiefly of particula te associations of F(filamentous)-actin was detected by the staining w ith rhodamine-labeled phalloidin. Stress-fiber-like structures were no t observed in each differentiation stage after day 10. Distribution of myosin, actin, and spectrin was studied immunocytochemically to know the role of them in the enucleation of erythroid cells that starts at late day 11 or early day 12 in the gestation. The enucleation is prece ded by the approach and the subsequent attachment of nucleus to the pl asma membrane. At that time, actin and myosin are present in the cytop lasmic and cortical region of the cells. From the time when the extrus ion of nucleus has started, condensation of actin and myosin was obser ved at the cell cortex area surrounding the extruding nucleus, and a c ontractile ring-like structure was infrequently observed. Spectrin was observed in the cortical region of the cells, and the change of the l ocalization of spectrin was not observed throughout the terminal diffe rentiation process (days 10-12) of the embryonic erythroid cells. The results show the possible involvement of a myosin-actin contractile sy stem that appears around the extruding nucleus within the mechanism of erythroid enucleation. (C) 1996 Wiley-Liss, Inc.