Role of the marginal band in an invertebrate erythrocyte: evidence for a universal mechanical function.

Marginal bands of microtubules are present in erythrocytes of all nonmammalian vertebrates and some invertebrates, in which they are thought to play a role in erythrocyte morphogenesis. Recently, marginal bands have also been implicated in maintenance of shape in vertebrate erythrocytes and platelets subjected to external mechanical forces. Here we demonstrate that marginal bands in an invertebrate ("blood clam") erythrocyte act similarly. Cells with and without marginal bands at the same temperature were prepared by (a) nocodazole or colchicine inhibition of marginal band reassembly following 0 degree C disassembly, (b) taxol inhibition of marginal band disassembly at 0 degree C, and (c) taxol induction of marginal band reassembly at 0 degree C. As shown previously for temperature-induced marginal band reassembly in this species, taxol-induced reassembly at 0 degree C occurred in association with centrioles. When erythrocytes with and without marginal bands were compared for their response to the mechanical stress of fluxing through capillary tubes, many more of those without marginal bands tended to become folded or buckled regardless of the method used to prepare them. The results provide evidence that marginal bands have a universal mechanical function in mature erythrocytes.