Analysis of erythrocyte-mediated microinjection by backscattered electron imaging.

The process of chicken erythrocyte-mediated microinjection of cultured BHK cells was studied by correlative secondary and backscattered electron imaging. The intense staining of the chicken erythrocyte nucleus by uranyl acetate was found to produce a backscattered electron signal sufficient to follow its position during cell fusion and microinjection. Initially, the erythrocyte ghosts were found to bind to the target cell surfaces. The microinjection process was complete within 2 to 4 hr, as evidenced by the presence of the erythrocyte nucleus within the cytoplasm of the target cell. By 24 hr, the internalized erythrocyte nuclei were difficult to distinguish by backscattered electron imaging. Some erythrocyte ghosts entered the cells intact by some method other than cell fusion, presumably phagocytosis.