Slow escape from mitosis

Cells with a defective spindle get delayed—stuck in a mitotic checkpoint—but eventually escape mitosis. In vertebrate cells, say Daniela Brito and Conly Rieder (Wadsworth Center, New York State Department of Health, Albany, NY), that escape is a gradual limp rather than a sudden exit.

The temporary stalling of the cell cycle in a checkpoint gives the cell time to repair damage before continuing. Ted Weinert and Lee Hartwell gave this phenomenon its name, but “they never viewed a checkpoint as leading to a permanent arrest,” says Rieder.

Indeed, even in response to a problem that cannot be fixed, such as high levels of the anti-microtubule drug nocodazole, many cells do leak through the mitotic arrest. In yeast and perhaps flies, the escape occurs via phosphorylation of Cdk1 or induction of a...