FIGURE 3. Cells expressing non-degradable cyclin B1 undergo mitotic exit reversal.

a, HeLa cells expressing non-degradable cyclin B1 can undergo mitotic exit reversal without segregating chromosomes. Flavopiridol was added at time 0 and removed at 25 min. Supplementary Video 7 shows the complete video sequence. b, HeLa cells expressing non-degradable cyclin B1 can undergo mitotic exit reversal after chromatid separation. Flavopiridol added and removed as in a. Supplementary Video 8 shows the complete video sequence. c, HeLa cells expressing wild-type cyclin B1 do not undergo reversal of mitotic exit. Flavopiridol added and removed as in a. Supplementary Video 9 shows the complete video sequence. Insets show GFP fluorescence images at time 0. The level of wild-type cyclin B1 in c is approximately twice that of the non-degradable cyclin B1 expressed in a and b. d, Cells expressing high levels of non-degradable cyclin B1 are more likely to undergo mitotic exit reversal. Black diamonds indicate cells that did not separate chromatids upon treatment with flavopiridol, red diamonds show cells with separated chromatids. Open red diamonds indicate two cells that recondensed their chromosomes but had not opened their cleavage furrows by 90 min after flavopiridol removal. Error bars show s.e.m. e, A mitotic HeLa cell at metaphase (arrow) expressing non-degradable cyclin B1 has low levels of cyclin A expression, as assessed by immunofluorescence. Scale bars, 10 m.