Membrane assembly and remodeling during reticulocyte maturation

Abstract

Membrane skeletal and cytoskeletal remodeling occurs throughout erythroid maturation. Microtubules and microfilaments have been identified morphologically in the nucleated erythroblast but the functional capability of these cytoskeletal structures during reticulocyte maturation has not been studied. Reticulocytes are formed from orthochromatic normoblasts by the process of nuclear extrusion. Two recognizable stages of reticulocyte maturation follow. The least mature reticulocytes are motile and multilobular, while the more mature reticulocytes are cup-shaped and nonmotile. To study the respective roles of microtubules and microfilaments in nuclear extrusion and cell motility, experiments were performed with agents that perturb these structures. Following the injection into rats of colchicine, a microtubule-disrupting substance, the number of normoblasts arrested at the stage of nuclear extrusion increased linearly over four hours. Similar results were obtained when bone marrow cells were incubated in culture in the presence of colchicine. In contrast, cell motility was dramatically decreased by cytochalasin B, a microfilament-disrupting agent, but not by colchicine. These results imply that microtubules are essential for the nuclear extrusion process, while microfilaments are essential for cell motility. Simultaneous changes in membrane skeletal assembly were assessed by measuring membrane deformability and stability, two properties regulated by the skeletal proteins. In ektacytometric assays, membrane deformability and mechanical stability of immature reticulocytes were markedly decreased to approximately 10% of normal, while that of more mature reticulocytes were nearly normal. Since the skeletal protein organization regulates these membrane properties, our findings imply that substantial membrane skeletal remodeling occurs during reticulocyte maturation. Thus we have identified major remodeling of both skeletal and cytoskeletal components during reticulocyte maturation.

A high‐resolution, double‐labeling method for the study of in vivo red blood cell aging

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Reticulocytosis in nonanemic dogs: increasing prevalence and potential etiologies

“…With Wright–Giemsa stain, reticulocytes appear as purple‐hued erythrocytes, referred to as polychromatophils. These have typically a wider diameter, and an irregular lobulated and larger surface area than mature erythrocytes; in addition, their cellular membranes are significantly less deformable and stable than those of mature erythrocytes . As reticulocytes mature, they transform from a spherical shape to the stereotypical biconcave disk through removal of extraneous cytoplasmic membrane; the intracellular hemoglobin concentration increases, and removal of cytoplasmic organelles is completed, typically over the course of 3–4 days …”

Protein and lipid trafficking induced in erythrocytes infected by malaria parasites

“…The organization of the red cell reflects these specialized functions as evidenced by high concentrations of cytoplasmic haemoglobin, prominent solute and ion transport systems and a deformable submembrane cytoskeleton. Mature red cells are also terminally differentiated, devoid of all intracellular organelles, incapable of de novo protein or lipid synthesis and lack endocytic machinery (Schrier, 1985; Chasis et al. , 1989).…”