Defective mitotic exit in Plk1-deficient megakaryocytes. (A) Representative mitotic progression and exit in wild-type megakaryocytes. Cells were transduced with lentiviral vectors expressing GFP-histone H2B (green) and mCherry-Geminin (red). Mitotic entry (time 0) can be monitored by chromosome condensation and pancellular staining of geminin. Mitotic exit (1 hour) is monitored by chromosome decondensation, reformation of nuclear lobules, and geminin degradation. (B) Two independent examples of defective mitotic progression in Plk1-deficient megakaryocytes. Mitotic entry (chromosome condensation and pancellular staining of geminin) is shown at time 0 (third frame in the top cell and second frame in the bottom cell). Geminin is slowly degraded 27 to 32 hours after mitotic entry, resulting in cell death (top cell) or mitotic exit (bottom) after approximately 37 hours. (C) Representation of cell fate in wild-type and Plk1(Δ/Δ) megakaryocytes. Every row represents a single cell. Geminin high phases are shown in red, whereas geminin low phases are in green. Endomitosis is indicated by a purple box and cell death is indicated by a red circle. Mitotic entry (condensation of chromatin and pancellular localization of geminin) is normalized as time 0. (D) Duration of mitosis (DOM; in hours) in Plk1-deficient or control megakaryocytes. Cdc20-deficient megakaryocytes¹²  are used as a control. ***P < .001; Student t test.