Lack of Plk1 results in defective centrosome maturation and spindle formation in mitotic megakaryocytes. (A) Reduced polyploidization in Lin^‒ bone marrow cells 3 days after stimulation with TPO. Data are mean ± SD (n = 4 mice per genotype). *P <0.05; **P < .01; ***P < .001; Student t test. (B) Representative images and quantification of mitotic cells (arrowheads) in these cultures 3 days after stimulation with TPO. Scale bars, 20 μm (top) and 50 μm (bottom). Data are mean ± SD. At least 250 cells per genotype were scored. ***P < .001; Student t test. (C) Immunodetection of Plk1 (red) in Plk1(lox/lox) and Plk1(Δ/Δ) stimulated in vitro with TPO. DAPI (blue) was used to stain DNA. Scale bars, 10 μm. (D) Quantification of ring structures in the mitotic cells in these cultures. Data are mean ± SD. n = 50 (control) or 250 (Plk1- or Cdc20-null) mitotic cells per condition. ***P < .001; Student t test. (E) Immunodetection of α-tubulin (green) and pericentrin (red) in Plk1-null or control cells treated with the indicated compounds. DAPI (blue) was used to stain DNA. Scale bars, 10 μm. (F) Quantification of pericentrin median fluorescence intensity (MFI) in these cultures. Horizontal bars indicate averages. ns, not significant; ***P < .001; Student t test.