Ultrastructure of megakaryocytes from a healthy bone marrow donor and an MDS patient. (A) Ultrastructure of a megakaryocyte from a healthy bone marrow donor demonstrating structural features characteristic for normal megakaryocytes. The right panel shows a higher magnification of the cytoplasm highlighting the demarcation membrane system (arrowheads). Original magnification × 3200 (left); and × 20 000 (right). (B) Ultrastructure of an MDS megakaryocyte showing chromatin speckles in the nucleus that has smooth outlines. The right panel shows the speckles (open arrowheads) and the poorly developed circular loops in the demarcation membrane system. Original magnification × 10 000 (left); and × 20 000 (right). Images were acquired using a Philips EM-201 electron microscope (Philips, Eindhoven, The Netherlands), diaphragm 30 μm; images were photographed directly by the microscope using 35-mm film from Eastman Kodak (New York, NY) and were subsequently scanned with a Heidelberg Topaz scanner using Linocolor 6.0 software (Heidelberger Druckmaschinen, Heidelberg, Germany). Images were further processed with Adobe Photoshop CS and Illustrator CS (Adobe, San Jose, CA).