The C-terminal domain determines the myosin II–specific localization in the contractile ring and its role in polyploidization. (A) CD41⁺ MKs from A⁺/A^ab heterozygous mice exhibit a specific localization of chimeric hNMHCII-AB protein in the contractile ring as revealed by an antibody against the C terminus of NMII-B (red) or by the GFP expression (green). Bars indicate 10 µm. At least 30 dividing MKs were observed with 6 heterozygous and WT mice in 3 independent experiments. (B) An antibody against the C terminus of NMII-A revealed no specific localization of NMII-A tail (red) in the contractile ring of CD41⁺ MKs from A⁺/A^ab heterozygous mice. Bars indicate 10 µm. At least 30 dividing MKs were observed with 6 heterozygous and WT mice in 3 independent experiments. (C) Expression of the chimeric hNMHCII-AB protein induces a decreased ploidy level of bone marrow MKs (left). Histograms show the total ploidy, the ≥8N ploidy level, and the ratio between 2N and 8N to 64N of bone marrow MKs from A⁺/A^ab heterozygous mice and control WT mice (right). (D) Expression of the chimeric hNMHCII-AB protein induces a decreased ploidy level of day-4 cultured MKs from A⁺/A^ab heterozygous mice compared with WT control mice (A⁺/A⁺) (top). Histograms show the total ploidy, the ≥8N ploidy level, and the ratio between 2N and 8N to 64N cultured MKs (bottom).