Immunogold labeling for wild-type and GATA-1^low MKs. Immunogold labeling for VWF of the cytoplasm from a stage III wild-type MK (A) and from representative light (B) and heavy (C) electron-dense GATA-1^low MKs. Representative immunogold particles are indicated by arrowheads. In normal MKs, VWF-immunoparticles are often localized at one pole of typical α granule structures. In comparison, the cytoplasm of GATA-1^low MKs contains lower numbers of gold particles localized both in α granule–like structures and in the cytoplasm (B). Note how few VWF particles are present in the cytoplasm of a heavy electron-dense GATA-1^low MKs. Original magnification × 30 000 for all panels.