Ultrastructure of platelet shedding MKs and platelets obtained in the presence of the combination of SCF, IL-3, and IL-6 from CD34⁺ CD41⁺ cells. (a) A similar mature MK as in Fig 9a with dilatation of demarcation membranes (dm) at the periphery (arrows) (N, nucleus). (b) Platelet-sized-fragments (P) are present with the combination of three cytokines. They are similar to those obtained with PEG-rHuMGDF (Fig 9b). On a proplatelet (PP), a constriction zone area is disposed along the cytoplasmic extension individualizing a distinct platelet field with a vacuole at the level of the future rupture (arrow) (A, α granules; sccs, smooth connected canalicular system; er, endoplasmic reticulum).