The cytoskeletal system of nucleated erythrocytes. III. Marginal band function in mature cells.

Open Access
Publisher Website
Google Scholar
Abstract
Marginal bands (MB) of microtubules apparently function during morphogenesis of nonmammalian vertebrate erythrocytes, but there is little evidence favoring a continuing role in mature cells. To test MB function, dogfish erythrocytes with and without MB were prepared at the same temperature by stabilization of the normally cold-labile MB at 0.degree. C by taxol and inhibition of MB reassembly at room temperature by nocodazole or colchicine. The responses of these cells to mechanical stress were then compared by fluxing them through capillary tubes. Before fluxing, cells with or without MB had normal flattened elliptical shape. After fluxing, deformation was consistently observed in a much greater percentage of cells lacking MB. The difference in percent deformation between the 2 cell types was highly significant. That the MB is an effector of cell shape was further documented in studies of the formation of singly or doubly pointed dogfish erythrocytes that appear during long-term incubation of normal cells at room temperature. On-slide perfusion experiments revealed that the pointed cells contain MB of corresponding pointed morphology. Incubation of cells with and without MB showed that they become pointed only when they contain MB, indicating that the MB acts as a flexible frame which can deform and support the cell surface from within. To test this idea further, cells with and without MB were exposed to hyperosmotic conditions. Many of the cells without MB collapsed and shriveled, whereas those with MB did not. The results support the view that the MB has a continuing function in mature erythrocytes, resisting deformation and/or rapidly returning deformed cells to an efficient equilibrium shape in the circulation.