Distinctive Cytoskeletal Organization in Erythrocytes of the Cold-Seep Vesicomyid Clam, Calyptogena kilmeri

Abstract

Erythrocytes have long served as model cells, useful for analyzing cytoskeletal structure and function. In non-mammalian vertebrates, erythrocytes are typically highly flattened, nucleated ellipsoids in which a marginal band (MB) of microtubules interacts with the membrane skeleton (MS) to generate and maintain cell shape. Though relatively rare, erythrocytes also occur in representatives of many invertebrate phyla, including the arcid and vesicomyid molluscs, but the structure and function of these cells are not well understood. Previous work has shown arcid erythrocytes to be highly flattened ellipsoids containing the MB-MS cytoskeletal system, similar to vertebrates but with an additional interesting feature: a functional centriole-containing centrosome associated with each MB. In the present study we have examined, for the first time, erythrocyte morphology and cytoskeletal structure in a vesicomyid. Using Calyptogena kilmeri, the dominant invertebrate at many Pacific cold seeps, we have found that the erythrocytes are only slightly flattened and do not contain MBs. Rather, their cytoskeletons display a peripheral centriole-containing centrosome with radiating fibers, a distinctive type of organization not observed previously in mature erythrocytes from any species.