Inhibition of Rock by Y27632 reduces furrow ingression. MKs transduced with H2B-GFP were treated for 12 hours with Y27632 and then filmed by real-time video microscopy. Cells were stained with CellTracker Red and serial images were obtained at 3-minute intervals. Timing (min) relative to the first image is indicated. (A) Diploid endomitosis of MK treated with Y27632 proceeded generally as a normal endomitosis, but with a reduced cell elongation (see also panel C) and less evident cleavage furrow formation. (B) Polyploid endomitosis of MK treated with Y27632 showing less cleavage furrow formation (images 21-36). These time-lapse images are available in Videos S3 and S4. (C) The distance between 2 centers of separating nuclear masses in mitosis and dipolar endomitosis was measured at end of telophase of Y27632-treated and untreated MK. In untreated MK (Control), the average distance reduced approximately 16% during endomitosis compared with mitosis. For Y27632-treated MKs, the average inter-nuclear distance of dipolar endomitosis was continually decreased approximately 20% compared with untreated MK.