Transmission electron micrographs of platelets from mice on day 4 after receiving carrier only (a and c) or a single intravenous dose of 250 μg/kg of PEG-rmMGDF (b, d, and e). Platelets produced in response to PEG-rmMGDF had normal ultrastructure, with the exception of frequent endoplasmic reticulum (arrowheads in [d] and [e]) and Golgi Complex profiles in platelet sections, suggesting their premature release. db, dense bodies; g, alpha granule. Magnification in (a) and (b) × 13,000, and in (c), (d), and (e) × 34,000.