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. The complete video sequence is available Supplementary Video 7. b, Hela cells expressing non-degradable cyclin B1 can undergo mitotic exit reversal after chromatid separation. Flavopiridol added and removed as in (a). The complete video sequence is available as Supplementary Video 8. c, Hela cells expressing wild type Cyclin B1 do not undergo reversal of mitotic exit. Flavopiridol added and removed as in (a). The complete video sequence is available as Supplementary Video 9. Insets show GFP fluorescence images at time 0. Level of the wild type Cyclin B1 in (c) was approximately twice that of the non-degradable Cyclin B1 expressed in (a) and (b). d, Cells expressing high levels of non-degradable Cyclin B1 were more likely to undergo mitotic exit reversal. Cells that did not separate chromatids upon treatment with Flavopiridol are depicted by black symbols. Those that separated chromatids are depicted in red. Two cells that recondensed their chromosomes but had not opened their cleavage furrows by 90 min after Flavopiridol removal are depicted by hollow red symbols. Error bars show S.E.M. e, A mitotic Hela cell at metaphase (arrow) expressing non-degradable Cyclin B1, shows low levels of Cyclin A expression by immunofluorescence. Bars = 10μm.