Intermediate Filaments of Endoskeleton within Human Erythrocytes.

Abstract

The mammalian erythrocytes had been considered to keep their deformable biconcave shape solely by the membrane and the underlying membranous cytoskeleton. However our previous study showed new aspects that human erythrocytes possessed a cytoplasmic endoskeleton apart from the classical membranous cytoskeleton containing beta-actin and neurofilament heavy chain (NF-H) [Terasawa K, et al. Arch. Histol. Cytol 2006; 69: 329–340]. Several studies showed that the intermediate filaments such as neurofilament light chain (NF-L), synemin and vimentin were detected in the nucleated erythrocytes [Granger BL, et al. Science. 1983; 221: 553–556] and extended from the nuclear envelope to the membranous marginal bands [Granger BL, et al. J. Cell Biol. 1982; 92: 299–312]. In the present study, we asked whether the intermediate filaments such as NF-L and vimentin also exist within the newly found endoskeleton of anucleated erythrocytes. NF-L and vimentin were detected within erythrocytes by western blotting and immunofluorescence. The NF-L were detected along the hillside filament group running parallel to the slope between convex periphery and the concave center and vimentin was distributed along several filaments in the whole erythrocytes by the ion-etching/scanning electron microscopy combined with immunocytochemistry. At the hillside region NF-L co-existed with vimentin along the hillside filaments by back scatter emission signals. We concluded that the endoskeletal filaments of the erythrocyte contain intermediate filaments such as NF-L, NF-H and vimentin as those of the nucleated erythrocytes of avian or lower vertebrates. The intermediate filaments of the endoskeleton within the erythrocytes may keep its unique biconcave disc shape against external circumstances.