Abnormal MKs observed by EM. Control MKs (Cont) are illustrated in thetop panel: (1) a normal mature MK, (2) DMS and granules shown at higher magnification, and (3) the formation of proplatelets (PP). Next is shown a panel of MKs obtained in vitro culture from CD34⁺ blood cells from P1 (i-iv) and from P3 (v-vii). Panel i shows heterogeneity in granule and DMS distribution in a large mature MK. Panel ii shows granules are present only in the peripheral ring, whereas the cytoplasm has a disrupted frayed structure with segments of cytoplasm devoid of granules, note also the presence of ghost structures in the center. In panel iii, the nucleus is still present; at the periphery fragments seem to be detaching from the main body of the MK and are often without granules. In panel iv, an abnormal proplatelet has granules concentrated in discrete zones. In panel v, a large MK from P3 has a heterogeneous distribution of granules and abnormal membrane complexes. In panel vi, an abnormal MK with at the periphery a ring-like proplatelet structure containing α-granules; there are signs of apoptosis in part of the cytoplasm and inside the nucleus. Panel vii illustrates immature α-granules (G) with several nucleoids inside of 1 structure. Bars indicate 1 μm.