Micrographs of PE-Ter119–labeled enucleating erythroblasts from mouse bone marrow and FVA cell culture. (A) Bright field illumination of enucleating erythroblasts, including nascent reticulocytes (black arrows) and extruding nuclei (white arrows). (B) Fluorescence microscopy of enucleating erythroblasts. Fluorescent intensities in nascent reticulocytes were greater than those in extruding nuclei, which indicated that GPA predominately partitions to reticulocytes during erythroblast enucleation. For scale reference, the diameter of the nucleus is 4.4 μm.