(A) Polychromatophilic normoblast and reticulocyte in bone marrow of SAD mouse. Parallel bundles of polymer fibers are noted in the cell periphery (arrow) of polychromatophilic normoblast and in cytoplasm of reticulocyte (arrowhead; original magnification × 6,372). Inset shows polymer bundles (star) in the cytoplasm as well as in the interchromatin regions of the extruding nucleus (original magnification × 18,720). (B) Polychromatophilic normoblast in bone marrow of SAD mouse showing cytoplasmic and nuclear polymer bundles with indentation of the nuclear envelope (original magnification × 10,000). (C) Reticulocyte in bone marrow of SAD/β^d3 mouse migrating through narrow gap in sinusoidal endothelium (SE). Polymers are restricted to the extravascular portion of the cytoplasm (arrow) compared with the intravascular portion (arrowhead) of a markedly deformed reticulocyte. An erythroid cell fragment (black star) is present next to migrating reticulocyte. A dense chromatin-like cap, probably a retained nuclear fragment, is seen involving part of the cell periphery of a polymerized reticulocyte (white star). No polymers are seen in intravascular erythrocytes. (original magnification × 7,500). (D) Reticulocyte traversing a wide gap in the sinusoidal barrier (SE), showing pointed extensions with polymer bundles oriented in the direction of the flow (arrow). A large geometric conglomerate of polymer bundles is seen in adjacent extravascular reticulocytes (arrowhead). Reticulocyte fragments (black star) are present next to reticulocyte in process of migrating through a narrow gap. Polymers are absent in the intravascular erythrocyte (original magnification × 3,000).