Impaired fetal liver erythroblastic island formation after palladin disruption. (A) Transmission electron microscopy image of E13.5 wt and Palld^−/− fetal livers. The erythroblastic island is composed of a central macrophage (M) and surrounding erythroblasts (E). In wt fetal liver, the connection between macrophage and erythroblasts is coherent, while this coherent connection is dispersed after palladin disruption. Note several phagocytosed nuclei (indicated as “N”) existing in mutant macrophage. (B) Native erythroblastic islands isolated from wt and Palld^−/− fetal livers were double-immunostained with F4/80 (green) and TER 119 (red) as described in “Materials and methods.” F4/80 is macrophage-specific marker, and Ter119 is the marker for erythroblasts. Note that Palld^−/− fetal liver cells could not form an erythroblastic island in this in vitro macrophage and erythroblast coculture assay. Images were viewed with an Olympus BX51 microscope with an Olympus UPlanFl 40×/0.75 objective, captured with a SPOT RTKE cooled color CCD camera (Diagnostic Instruments), and imported into SPOT software (Diagnostic Instruments). FITC (F4/80⁺ cells) and PE (Ter119⁺ cells) fluorescence are shown. Original magnifications, × 3000 (panel A) and × 400 (panel B).