Cellular localization of ¹²⁵I-rTpo within the sternum of NF-E2-null and control mice analyzed by electron microscopic autoradiography. Autoradiographic silver grains associated with a large abnormal megakaryocyte from a mouse lacking p45 NF-E2 (A) or a megakaryocyte from a control mouse (C) are circled. (B) Release of an anucleate platelet-like structure, capable of binding ¹²⁵I-rTpo (circle around the autoradiographic silver grain), into the vascular space of an NF-E2-null mouse. Bar, 2 μm.