Polyploid MKs in prometaphase. Cultures were performed as described in Fig 1, except that nocodazole (1 μg/mL) was added in some experiments to 8-day culture for 5 hours. Cells were stained either by May-Grünwald Giemsa or labeled by antibodies (FITC or TRITC) and counterstained by the Hoechst dye (blue) after cytocentrifugation and fixation. (a) This MK is blocked in pseudometaphase by nocodazole. Well-condensed, individualized chromosomes are present. The cytoplasm already has a granular pattern with purple staining localized to one pole of the cell that may correspond to granules (arrow). The nuclear envelope is not apparent. Original magnification × 2,000. (b) Two large MKs (appointed by arrow) are labeled by an anti-vWF antibody (FITC) and conterstained by Hoechst. These endomitotic MKs with condensed chromosomes are blocked in prometaphase. Original magnification × 1,000. (c) An MK in interphase is labeled by the human anti-lamin B antibody (TRITC). The polylobulated nucleus is surrounded by a distinct linear red labeling. Original magnification × 1,000. (d, e, and f) A polyploid MK in spontaneous metaphase is shown. Expression of vWF (FITC; d), Hoechst (e), and lamin B (TRITC; f). Only a faint and dispersed labeling is observed in TRITC, demonstrating that the nuclear envelope has disappeared.